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Checked when installed. There is no slack movement on the calipers, although if I use a bit of manual pressure I can move them slightly. But that's what I expect from single-sided sliding pin calipers with the master cylinder at rest position. All the ports are open so fluid can be pushed back to the reservoir. If they don't move a little the pins and/or pistons are seized. For years I did this test every month or so on a Honda m/c I used through the winter. Useless pin seal design meant the pins seized and needed to be stripped and regreased 2-3 times a year.
 

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Discussion Starter #22 (Edited)
Seems like pedal travel is a personal observation, possibly.
I find that (for me), pedal free play feels to be significantly more underfoot than it actually turns out to be if actually measured, so yes I think the perception is quite subjective. And of course what one person finds quite acceptable, another person might find to be quite problematic.

It's particularly objectionable for me because I habitually 'heel / toe' for most downshifts, and excessive free play very significantly affects this, i.e. makes it much harder to do, and the performance of it variably less precise and so less satisfying (at least with my level of skill). Getting this wrong makes me feel like a bit of a klutz, but with the improved pedal action this is now quite rare...

If the car has an automatic gearbox, then I don't really care all that much if the free travel is a bit excessive (don't care about automatic cars, just don't like auto boxes).

Stainless braided brake hoses remain a tried and trusted remedy but I'll still have a closer look at the cylinder retraction.
I'd suggest that the place to look first isn't the seal related piston retraction, but the loose fit of the pins in the bracket bores. Using a thicker pin grease may well help too, thinner grease may allow somewhat more radial movement between the pin and bore (I've used a 'red rubber grease', very thick, quite hard to squeeze from the tube...). The pins are the real problem, the seal retraction is just a minor annoyance...

IMO braided lines are a good thing, if not as much of an improvement as many seem to think (over rubber hoses in good nick). Whatever, I don't think braided hoses will help much with pedal 'free' travel. They should improve the pedal travel and feel once pedal input becomes high, but not much at all with light inputs (when the system pressure is too low to 'swell' the hoses significantly). Braided hoses won't significantly diminish 'free' travel, where the pedal moves significantly before any significant system pressure starts to be generated, but once the driver is pushing the pedal quite hard, then yes, probably worthwhile fitting.

Regards,
John.
 

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Discussion Starter #23 (Edited)
Checked when installed. There is no slack movement on the calipers, although if I use a bit of manual pressure I can move them slightly.
So there is some "slack", there it is, right there. It doesn't take much...

But that's what I expect from single-sided sliding pin calipers with the master cylinder at rest position.
I don't really know, but it wouldn't surprise me at all if 'fixed' calipers (with opposed pistons) were generally designed with less seal induced piston retraction (at each piston) than single piston sliding pin calipers are. If this is a correct speculation, it would be to account for there being at least twice as many pistons directly acting on both sides of the pads and disc (than with a single piston sliding caliper, with only one piston acting on both sides of the disc, one side directly and the other indirectly). This would be to prevent clearances becoming truly excessive, with consequent and potentially very excessive free pedal travel. If I were designing a braking system from scratch, this would be something I would be keeping in mind...

With a 'fixed' caliper there will still be some pad retraction, it just can't be detected by pushing and pulling on the caliper body, because the caliper is fixed. No part of the caliper body can move (other than by flexure caused by high system pressure), only the pistons. The most you'll see / feel is some degree of looseness between the pads, the caliper, and the disc. The clearances still have an affect on pedal free travel.

All the ports are open so fluid can be pushed back to the reservoir.
Of course, for a few reasons the ports have to be open if no braking is occurring. This isn't causative to the pistons being retracted by the seal or being pushed back too far (knock back). It just permits it to occur, whether to a wanted degree, or not. If it is a sliding caliper, and its' body is moving significantly in any direction other than purely in / out, then this will tend to 'knock back' the pads, and so the piston.

Whenever the piston is pushed out against the pads / disc, when the force that moved it outward is removed, the piston won't move back of its' own accord. It will remain fully 'out' unless some other force causes it to be pushed or pulled back into the bore (whether to a very small or fairly large degree). This will either be a retractive force associated with the seal, and / or a force associated with knock back, i.e. axle flexure, movement caused by worn bearings, disc runout (same thing in effect as axle flex or worn bearings), or, the caliper body flopping around in directions other than in / out.

Fixed calipers can't move, so at least one of these things doesn't apply to them.

If they don't move a little the pins and/or pistons are seized.
They'll move because there is a piston / pad / disc clearance (pads retracted, and maybe 'knocked back' as well), not because of anything not being seized. This is a different issue. The test is whether or not the caliper body will easily slide on the pins when the pads have been taken out.

Regards,
John.
 

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I have the same "problem" as John described regarding free pedal move. Simply it doesn't provide confidence especially when traveling on highway. My rear calipers also produced knock sound on certain bumps and uneven roads. This was remedied by replacing rear shocks which just masked excessive play on rear calipers. I've refurbished them and also have braided hoses but it didn't help. Only thing left is replacing pin with insert with solid one like John suggested or do what my mechanic said and "fix" pin bores by making them smaller so there is no more wiggle but I don't think it will solve pedal movement.
Also Fruity mentioned ABS problem and it's also true especially on unpaved roads driving downhill. ABS kicks in too early and car is simply not stopping....
 

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Let's return to the pedal free movement. I have 15-20mm where nothing happens, beyond that, the brakes begin to work, and it's progressive. Obviously I can't measure this whilst driving, but it feels like 15-20mm, and looking at my foot while braking confirms that. Under an inch, anyhow.

The diesels (maybe other 147's - I dunno) do have a slight softness to the pedal, but I'm told that's due to the ABS design and servo ratio. There isn't the rock solid feel of a simple, unassisted braking system, just some compliance is introduced, as if there's a compressible latex pad on the pedal. If I try and brake with no vacuum (engine off, servo reservoir empty), then the solid feel is there - but I need both feet and a crowbar to stop the car in less than a quarter mile from 30mph.

I don't find this softish pedal action any sort of problem, I can tell what the brakes are doing. Braided hoses have made the feel/feedback better (there was a degree of vaguess with 10 y.o. hoses, as if the compressibility of the imaginary latex pad was variable), but that's all.

Are either of you seeing more than 15-20mm free movement at the pedal? If so ISTM that'll be due to a fault, not inherent, else my car would be the same.
 

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BTW the ABS unit on these cars includes a pump for ABS, ASR (traction control) + VDC (stability control). I've felt that pump work, using cruise control on a long steep downhill, with feet off the pedals. If the car starts to exceed the set speed, the pump briefly applies some braking to all 4 wheels. Only slight, but noticeable and repeatable, after a remap. I assume changed fuel quantities confused cruise control's ability to limit speed. The ECU seems to have relearned new parameters since.

I only mention this because it's a complicated hybrid mechanical and brake-by-wire system, and that may explain some of the 'latex' pedal feel.

I've no experience of ABS operating prematurely to lengthen braking distances. It should only operate as the wheel starts to slip and then restore braking effort as soon as wheel rotation is re-established, automated cadence braking, though I suppose VDC must supervise that. Has this happened with no dash warning?
 

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Things I agree on:
Pedal free travel is too long and is not as nice as early 156- especially for heal and toe down changes but then again, the JTS throttle is neither as sensitive or linear as CF2 TS.

Standard hoses impart a rather spongey feel once pads touch the discs.

Later ABS/VDC system provides inferior pedal response. I find it also interferes with braking function whilst turning steering wheel at high speed. (Downhill <especially> braking on unpaved surfaces will be worse due to wheel-skip)- better front dampers/lighter wheel/tyre combination should help.

Rear caliper pins are a likely factor. Handbrake travel is less with new, more compressible rear brake pads (to begin brake effect) than with worn, less compressible pads. The only obvious difference is the caliper slide pins are further into the carrier with new pads which gives less radial movement of the pins. Viscous grease helps. I used to have REALLY thick red grease (50 years old) which I think was a marine grease.
 

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Discussion Starter #28
I don't find this softish pedal action any sort of problem, I can tell what the brakes are doing. Braided hoses have made the feel/feedback better (there was a degree of vaguess with 10 y.o. hoses, as if the compressibility of the imaginary latex pad was variable), but that's all.
But, are you trying to 'heel / toe'? This is when the unwanted and erratic pedal free play becomes a real problem (especially with the stock pedal placement, which doesn't any longer apply to my car as the throttle pedal postion has been modified to better facillitate 'heel / toe'). If you aren't 'foot dancing' then the brake pedal free play is much less of an issue.

It's all about relative 'working' pedal height, ie. when the brake is firmly applied, is the brake pedal at the same height or a tad higher than the static throttle pedal height? Or, is the applied brake pedal lower than the static throttle pedal? If the brake pedal pad is lower than the throttle pedal, then it is very difficult to roll the foot over onto the throttle pedal to 'blip' the throttle, simply because the static throttle pedal height is higher than the 'working' brake pedal pad.

Of course the degree to which the brake pedal continues to move after all the free play 'slack' has been taken up (i.e. heavier brake application) has a very significant affect on this as well. This is where braided hoses can be useful, i.e. to reduce 'loaded' pedal travel. However, if the stock hoses are in good condition, IMO the 'free' play is much more of an issue...

Whatever, most of the problematic free play I was experiencing has been substantially reduced by changing the pins, leaving only the free play that I am attributing to seal induced piston retraction, for which I can see other cause. I can live with this, for now.

In any case, what brake pedal feel one person likes might not be the same as another person likes. I recall driving someone elses racing kart; when I came back into the pits I told him that there was something very wrong with his brakes, the pedal was way 'long' and very spongey (I hated it). The karts owner, a very experienced and competitive racer, then told me that he deliberately always left a bit of air in his brake hydraulics, because he much preffered the long travel and soft feeling brake pedal (takes all kinds...). 'Heel / toe' isn't a 'thing' with karts, he might not have liked it so much if it were...

If your old hoses were in fact knackered, then I don't think they can be used as a benchmark against which whatever improvement braided hoses might create can be compared. There is also at least a possibility that when you changed the hoses, that when you bled the system you may have purged some air that might have been in there with old hoses...?

Are either of you seeing more than 15-20mm free movement at the pedal?
I now have about 3 cm of free pedal travel if I don't 'tap' the pedal (subjective). When I do tap the pedal, this becomes about 2cm (doesn't sound all that much of a difference, but makes a big improvement in the ease of 'heel / toe' action). Previously (before changing the pins), the 'untapped' pedal free travel could be up to about maybe 4cm, but I could subsequently get about 2cm of free travel by 'tapping' the pedal, but only sometimes, other times the 'tapping' just didn't work, or only partially worked. With the new pins, this is now much more consistent.

I suspect that this is because when the caliper body was able to move more on the looser fitting pins (in unwanted directions), the piston would pump out on the first 'tap', but immediately the caliper body would move again as soon as the pedal was released prior to the next 'real' brake application. So, the piston was immediately knocked back in the bore, so the 'tap' was a waste of time (but not every time). With the new tighter fitting pins, the piston pumps out on the 'tap', but the caliper body doesn't wobble as much during the brief time between the tap and prior to the next push, so the piston doesn't get 'knocked back' and the tap works much more consistently.

Note that with the new pins, the quaility of the pedal 'free play' has changed. With the floppy pins (one in each rear caliper) the free play was very free, in that the pedal felt to provide virtually no resistance at all in the first part of the pedal travel. With the new pins, the 'free' travel doesn't feel entirely 'free', in that some slight resistance can be felt in the first part of the travel.

If so ISTM that'll be due to a fault, not inherent, else my car would be the same.
I don't think the piston retraction in my brakes is a 'fault' per se. There is no other source of pedal free play that I can identify, but I can isolate rear caliper piston movement (in and out, which strongly implies seal related significant piston retraction) that is 'taken up' in the first two or so cm of pedal travel, after which the pedal becomes firm. Everything points to this piston retraction as being the source of the remaining unwanted pedal travel (i.e remaining after changing the pins).

Piston retraction is a deliberate 'feature', intended to eliminate pad drag. There is no such thing as a 'free lunch', the compromise is increased free travel at the pedal. This is inherent in the design. I suspect your car is actually similar (though obviously can't prove it to be), but that your perception of it as being problematic or not varies to mine.

The use of one pin in each rear caliper (having a rubber insert) is also obviously deliberate. It also obviously contributes to pedal free play, of the more unfortunate kind (i.e. erratic). The brake designers must have some reason to do this, but it's a mystery to me what this could possibly be (and consider that not all quite similar rear calipers use a similarly weird pin...). All I know is that my brakes are much much better with this 'feature' removed...

Regards,
John.
 

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Discussion Starter #29 (Edited)
Rear caliper pins are a likely factor. Handbrake travel is less with new, more compressible rear brake pads (to begin brake effect) than with worn, less compressible pads. The only obvious difference is the caliper slide pins are further into the carrier with new pads which gives less radial movement of the pins.
The rear caliper pins (with the insert) are also significantly shorter than the all steel pins. From memory this is about 1cm shorter, the pin only reaching about half way into the bore (the all steel pins go further in). There is plenty of depth in the corresponding bracket bore to accomodate the longer all steel pins, both bores being the same depth.

My brakes work very nicely (i.e. much better) with all steel pins of the same length and uniform closely fitting OD along their entire length. So why exactly is it that the insert pin is shorter? Why is it that the OD is so different along their length? Other than the brake designers, nobody knows, it's a mystery...

The only part of the insert pin that is in close contact with the bore is the short insert. The pin shank is much smaller OD than either the bore ID or the insert. The pin 'pivots' on the somewhat pliable rubber insert but isn't significantly radially constrained anywhere else along its' length. This allows the shank to radially move at the point where it exits the bore (up / down / backward / forward). That the pin is firmly bolted to the caliper body does inhibit this radial movement, due to the pins being firmly attached to the caliper body.

Yet despite this, most of the unwanted caliper body movement does seem to be associated with the insert pin (can be seen visually). This implies some hard to see and very slight flexure (bending and / or twisting) in the caliper body arms (at the end of which the pins are bolted), maybe. I can't see any such flexure occurring, but am inferring it's existence because of the movement that I am seeing...

With the insert pins, if the caliper body is 'wiggled' up and down (the up / down force exerted at the inner end of the caliper, near the handbrake mechansim), this generates not only up and down body movement, but also some inward and outward movement of the pins in their bores. The whole caliper body tilts, with an arc of rotation centred somewhere between the upper and lower pins. This ought to be prevented by the close fit of the one all steel pin, but this only seems to partially inhibit it (hence my suspicion that the caliper arms are flexing slightly, even though the forces invloved are not all that great).

Because the caliper body movement is actually a 'rotation' in an arc centred between the pins, this pin movement is opposite at each pin, i.e if the upper pin is moving in then the lower pin is moving out (and vice versa). This axial movement appears to occur to a greater degree at the insert pin that at the all steel pin. If all steel pins are fitted in place of the insert pins, this axial pin movement still occurs but is significantly reduced at both pins (as is the 'tilting' of the caliper body), and appears to be of equal magnitude at both pins (though still in opposite directions).

So why do these pins even have an insert at all? Why didn't the designer use an all steel pin identical to the other pin used? Nobody knows, another mystery (well maybe the brake designers know, but they don't seem to be telling anyone). The whole insert pin thing is just weird, seemingly unnecessary and counter-productive.

Viscous grease helps. I used to have REALLY thick red grease (50 years old) which I think was a marine grease.
The 'red rubber grease' that I used is very thick, and it's new. It's actually quite difficult to squeeze it from the tube...

I think many or most of these rubber compatible greases are generally vegetable based, i.e. castor oil based. Castor bean based oil was for years and years the oil of choice for nearly all racing engines, only supplanted by highly engineered modern mineral and synthetic oils (the synthetics often vegetable oil based). It's still not commonly used in high revving two stroke race engines (particularly kart engines).

Regards,
John.
 

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No, I don't normally heel and toe in this car. I've done it routinely in some others, especially Mk1 Golf Gti, but in most cars the pedal layout is wrong. It's not comfortable in the 147, and besides, it's a diesel tractor, with a rather slow gearbox. There's little reason to raise the revs to match the gear when there's no power band to stay in, it all happens at 1500-3000rpm

My pedal doesn't pump up noticeably through tapping the pedal.

I assumed that the plastic collar on the lower pin was to provide some friction, so that caliper displacement was damped. To that extent I'd expect removal of the plastic to increase retraction due to seal design, as there would be less resistance.

I don't understand your earlier point that the caliper is rigidly mounted. It's secured by the sliding pins to the pad carrier saddle (which is rigidly mounted to the hub carrier), and the caliper moves in-out to equalise force on inner and outer pads. That is where I find no detectable slop. The pads are as close to the disc as they can be without any drag or excess clearance, although I can move the caliper a little in-out on the pins with a bit of force. That seems correct on a single-sided piston, sliding-pin design.

Anyhow, I'm clearly not helping, so I'll leave it here.
 

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Discussion Starter #31
No, I don't normally heel and toe in this car. I've done it routinely in some others, especially Mk1 Golf Gti, but in most cars the pedal layout is wrong. It's not comfortable in the 147,
Yes, pedal layout is wrong for 'heel / toe' with most cars, the 147 is not an exception. With many cars 'heel / toe' is almost impossible. This is why I've modified my throttle pedal position, but even so it was still quite awkward to heel / toe, until I fitted the all steel rear caliper pins (reducing pedal free play).

The 147 throttle pedal pad is attached to a very stiff steel arm, much stiffer (thicker) than it really needs to be, which is very difficult to bend in order to relocate the pad, but I managed to do it. The problem is that if mindless brute force were to be used in situ there is a real possibilty that the mechanism could be damaged or broken. The stiff arm is attached to what looks to be a quite fragile mechanism. It would be better / safer if the pedal etc. were removed from the car before attempting to modify the arm, but I had a "cunning plan"...

and besides, it's a diesel tractor, with a rather slow gearbox. There's little reason to raise the revs to match the gear when there's no power band to stay in, it all happens at 1500-3000rpm
I've not driven the diesel version (or any other 'high performance' turbo diesel for that matter), but I do assume all that low rpm 'grunt' does tend to pull the car out of corners quite well regardless (almost) of the gear you happen to be in.

My pedal doesn't pump up noticeably through tapping the pedal.
That is either lucky that a pedal 'tap' is not needed, or unlucky that if it is needed, it doesn't work...

I can't recall driving a car where the pedal didn't in some degree 'come up' after a 'tap'. It seems pretty ubiquitous. Having said that, my 147 wouldn't do it consistently, until I ditched the insert pins. I had a somewhat similar isue with my old Accord, but this was caused by worn pins (no insert pins, all steel, fixed by wrapping thin brass shim around each pin...).

I assumed that the plastic collar on the lower pin was to provide some friction, so that caliper displacement was damped. To that extent I'd expect removal of the plastic to increase retraction due to seal design, as there would be less resistance.
A very reasonable theory, and one which frankly hadn't occurred to me. To provide a damping friction could be very useful, and probably why it seems better to use a thick pin grease rather than a thin grease...

I think the reason that this idea hadn't occurred to me is that I haven't ever come across an insert pin that didn't slide quite easily in the bore, with no noticable frictional resistance (other than because of rust etc.). The insert would need to be a slight interference fit in the bore. I haven't ever come across one which was, but then I haven't ever disassembled a near new caliper, only older ones where there is at least a possibilty that the insert was significantly worn.

On my desk is one of the pins I have deleted, and it visually appears to be unworn, no rough or shiny areas on the high contact areas of the 'flutes' (the low non contact areas of the flutes have the same surface appearance). I know that the pin is 0.1mm smaller than the bore it came out of, which could mean that this is the intended clearance, or, that some wear has occurred, despite not looking worn in any way...

But, if so then why not use an insert pin in the front calipers, for the same reason?

I don't understand your earlier point that the caliper is rigidly mounted. It's secured by the sliding pins to the pad carrier saddle (which is rigidly mounted to the hub carrier), and the caliper moves in-out to equalise force on inner and outer pads.
Not sure where I might have said something which could be interpreted as meaning that the calipers were rigidly mounted? The caliper body isn't rigidly mounted, but it is rigidly attached to the pins (bolted to them), and the 'saddle' is rigidly attached to the 'hub carrier'. The only movement that can occur is where the pins fit into the bores in the 'carrier'.

Of course the pins are supposed to slide axially in the pin bores. They aren't supposed to move radially, because (as I seem to have found) this will create whatever degree of pad knock back as the body wobbles up / down / backward / forward (or at least has the potential to do so, which seems to be what was happening with my rear calipers). If the pins are a loose fit (or only one pin is), then this is a problem.

That is where I find no detectable slop. The pads are as close to the disc as they can be without any drag or excess clearance, although I can move the caliper a little in-out on the pins with a bit of force. That seems correct on a single-sided piston, sliding-pin design.
Isn't that an inconsistent observation? "No detectable slop" and "I can move the caliper a little in-out on the pins with a bit of force" are I think mutually exclusive statements.

If it is at all possible to manually move the caliper body in / out on the pins, then the strong implication is that the piston must be retracted in some degree. It is theoretically possible to move the caliper body along the pins if the piston is not retracted, but to do so would mean that the force used would need to be great enough to slide the piston in the seal. Don't know about you, but my hands are nowhere near strong enough to do this.

How hard is is to manually push a caliper piston into the bore with the caliper dismounted? Very, I've never managed to do it, always needing some sort of compressing tool to achieve this. So IMO, if it is possible to manually move the caliper body in / out at all, then I think it is almost certain that the piston is in a retracted state...

Anyhow, I'm clearly not helping, so I'll leave it here.
I have a habit of arguing my point to death. I think it has been an interesting discussion.

Regards,
John.
 

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Discussion Starter #32
Halftone suggested that the caliper pins’ rubber insert might (if unworn) be intended to create some frictional 'damping' between the pin and the pin bore. I assumed my inserts were not worn since they didn’t look to be, and therefore were not ‘frictional’ in nature. On the assumption that I was perhaps wrong about this (i.e. that despite appearances my inserts were worn and should be a tighter fit in their bores), I’ve changed tack on this experiment.

I removed the new all steel pins. I then took the inserts off the old pins (they just slide off fairly easily, and are definitely rubber or a rubber like material, not plastic), and inserted a strip of copper shim between each insert and the pin, wrapped around the pin. This was 0.1mm shim cut to the width of the pin recess in which the insert fits (the shim must be a very close fit to the width of this recess, or the shim will axially move on the pin, and thus so will the insert). I wrapped the shim strip around the pin shaft maybe three times (didn’t actually count), then slipped the insert back over the shim and pin. The ridges of the insert recess are deep enough to hold both the rolled shim and the insert in position (annealing the shim makes this easier and makes for a tighter shim wrap).

This expanded the insert, which now measured 10.5mm diameter (as opposed to 9.9mm previously). So, in a 10mm bore this was an interference fit of 0.5mm (i.e. the insert has to be compressed by 0.5mm in order to slide into the bore).

However, the pins wouldn’t slide all the way in. When nearly all the way in the rubber would slip along the shim and expand over the locating ridge on the pin (even when all grease had been removed from between the shim and insert), which prevented the pin from moving further into the bore (the rubber expanded over the ridge and ‘jammed’ and so the pin wouldn’t slide further). I then cut about 15mm from the shim strip, so the insert was less expanded. The insert diameter then measured 10.25mm diameter, and did slide all the way into the bore with some modest force.

So now there is some significant friction between the pin, the insert and the pin bore. The pin no longer slides in / out with no resistance, it takes a firm push or pull on the pin before it slides, which is what I was after. The other (insertless) pin still slides in / out very freely as before. It is still possible to manually rock or tilt the caliper body, but the only ‘in / out’ movement that occurs is at the pin without the insert, so this unwanted motion is significantly less.

I then did the same to the other rear caliper.

On the road the pedal free play is now only slightly better than with two freely sliding insertless all steel pins in each caliper. I was hoping for a bit more than I got (or a bit less, depending on how you look at it), but there is some improvement in pedal free play, and the consistency of it when ‘tapping’ the brake pedal.

If I manually push / pull on the caliper body the insertless pins slide very easily, the insert pins quite a bit less easily (if I push / pull firmly enough I can make them move, they aren’t overly ‘tight’, and certainly a long way from ‘seized’). If I use some force I can still move the caliper body in and out about 1mm, which I’m quite sure is a product of the piston retraction created by the cup seals. There is no brake drag.

I’m wondering if further improvement (to the caliper body ‘wobbling’) might be had if the remaining insertless all steel pins were to be replaced with insert pins, if, the inserts were expanded as described above. This would mean that both pins in each caliper had some friction between pins and pin bores, and therefore wouldn’t move ‘in / out’ with very little provocation. I’m sure that there would still be some pedal free play caused by piston retraction, but less because it isn’t added to by caliper body ‘wobble’.

Alternatively, possibly better, the insertless pins could have two or three grooves machined into the shafts (near the ends of each shaft), into which rubber O-rings could be fitted. If the O-rings protruded slightly proud of the pin shafts then they would have to be slightly compressed into the bores, which would create some axial friction (as well as improved radial pin location).

So, whether shimmed insert pins or modified steel pins (with O-rings) were used for all pins in each caliper, there would be at least some resistance to sliding in / out with both pins, so unwanted ‘wobbling' might be all but eliminated (or at least substantially reduced). The caliper pins should still slide freely enough in the bores that pad wear is accommodated without caliper seizure. This would (potentially) eliminate pedal free travel caused by the rear calipers wobbling on the pins, but there will still be the free play caused by piston retraction...

Regards,
John.
 

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Discussion Starter #33
I’ve been saying that the front and rear calipers were the same in principle, and to a substantial degree they are (ignoring the handbrake mechanism). But, I had the front calipers off the other day to grease the pins, and when looking closely at the bushes realised that they were entirely rubber. All the pins are 'all steel', and don’t slide in metal bushes at all.

There is some friction between the pins and bushes because the pins are slightly larger in OD than the bush ID. This does cause some resistance to the pins axially sliding in the rubber bushes, but not a great deal (unless perhaps my front caliper pin bushes are a bit worn, which is at least possible).

Unlike the rear calipers, it’s quite difficult to manually ‘wobble’ the front caliper bodies, they are quite firmly mounted (much more so than the rear ones). However, if the anti-rattle spring is removed, it becomes quite easy to wobble them quite a lot (possibly not all that surprising considering the bushes are only rubber). It’s obvious that quite a bit of the ‘wobble control’ is a function of the anti-rattle springs. Such springs would probably be a ‘good thing’ if something similar could be adapted and fitted to the rear calipers...

Regards,
John.
 

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Discussion Starter #34
The experimentation continues:

I machined four grooves into the two all steel pins and fitted O-rings into each groove. The O-rings are somewhat stretched when sitting in the grooves, and are 'proud' of the pin OD. The pin OD is 9.9mm, the bore ID is 10mm, the OD of the stretched O-rings is 10.25mm, so must be slightly compressed in order to fit into the bore (I first tried the O-rings at 10.35mm, but at this diameter they couldn't be fitted into the bore, not even with a lot of of force, because the O-ring woud 'catch' on the edge of the bore).

The pins now look like these pins:

https://www.google.com.au/imgres?imgurl=http://i892.photobucket.com/albums/ac129/md_auto/9A2AC0B3-ED23-45F2-A4E5-2B2C3616E8F1-1519-000001B17B517421_zps0b6bafd7.jpg&imgrefurl=https://forum.lowyat.net/topic/2923257/+220&docid=HDWts2us5Jk_sM&tbnid=KZ1yz_UIMwicUM:&vet=10ahUKEwj_272V4onfAhUDTI8KHUcqCXwQMwhOKAswCw..i&w=1024&h=768&bih=726&biw=1344&q=myvi brake pins kok&ved=0ahUKEwj_272V4onfAhUDTI8KHUcqCXwQMwhOKAswCw&iact=mrc&uact=8

Note that the O-rings on my pins don't protrude as far from the pin OD as the ones in the linked image do.

So now each caliper has one pin with an expanded insert (tighter fit in the bore), and one with four O-rings fitted. Both pins will smoothly slide in and out with some force manually applied, but are not 'free' to slide with no resistance, there is some significant friction. The caliper body is now quite firmly located and cannot be easily 'wobbled' by hand.

To recap; Previously, with un-molested stock pins, the caliper body could be manually wobbled very easily to a substantial degree, and pedal travel was quite excessive, and inconsistent.

Experiment 1:
Replacing the 'insert pin' (so that each caliper had two 'all steel' insertless pins) improved this significantly. Wobble was lessened and pedal travel / consistency improved. In both cases the caliper 'wobble' was largely associated with the pins moving in / out but in opposite directions, i.e. as the upper pin moved in the lower pin moved out, and vice versa. Replacing the insert pin with an insertless pin improved this, but didn't eliminate it.

Experiment 2:
Swapping two of the all steel pins back to orginal 'insert pins' (i.e. one insert pin in each caliper), but in which the inserts had been expanded (by wrapping shim foil between the pin and the insert) improved this more. The expanded insert pin was resistant to moving in / out, all such movement now occuring at the all steel pin only. Pedal motion and consistency improved compared to both the unmodified stock pins and compared to fitting 'all steel' insertless pins (ie. all pins).

Experiment 3:
Now, each caliper has an expanded insert on the 'insert pin', and a modified 'all steel' pin with four O-rings (as above). With the pads removed, the caliper body can be manually pushed in / out with some force, but isn't 'free'. 'Wobble' is very much reduced.

On the road the pedal travel is very significantly improved, less travel and more consistent than stock or with experiments 1 or 2. Some free travel still exists, which I am attributing to piston retraction associated with the seals (with both rear and front calipers).

However the pedal 'comes up' very easily and consistently with one 'tap' on the pedal, and the pedal is then firm and confidence inspiring. Heel / toe is easy and consistent, so long as the pedal has been 'tapped'. In general, pedal feel is improved / good and travel reduced even without 'tapping' the pedal.

Jacking the rear wheels off the ground and spinning the wheels, the wheels rotate easily, about the same as they do with no modifications to the pins. But, it is obvious that at least one pad at each caliper is in some contact with the disc. It can be heard and subtley felt as the wheel is rotated. The contact is light, and I don't expect it to cause any issues.

I'm fairly confident that the rubbing pads are more likley to be the the outer pads. The caliper body doesn't move freely because of the tighter fit between the pins and the pin bores, so the caliper body tends to remain in the same position when piston stops exerting force. The outer pads don't move as the brakes are released, other than to a very small degree as the clamping force is released, leaving them in very close proximity to the discs (but without any significant force pushing them against the discs). However, the pistons will still be retracted by the piston seals, so when the brakes are released a small gap will appear between the pistons and the inner pads. The inner pads will then be free to 'rattle' slightly away from the discs, or just to very lightly 'kiss' against them.

All in all, I'm very pleased with the improvement, night and day compared to how it was with the untouched stock pins. There is still some room for improvement, the piston retraction is still an issue (probably), but might prove difficult to address. A 10lb residual pressure valve would probably cause too much brake drag, a 2lb RPV may not be strong enough to prevent retraction. Still, a 2lb valve might at least reduce the retraction...

Regards,
John.
 

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The experimentation continues:

I machined four grooves into the two all steel pins and fitted O-rings into each groove. The O-rings are somewhat stretched when sitting in the grooves, and are 'proud' of the pin OD. The pin OD is 9.9mm, the bore ID is 10mm, the OD of the stretched O-rings is 10.25mm, so must be slightly compressed in order to fit into the bore (I first tried the O-rings at 10.35mm, but at this diameter they couldn't be fitted into the bore, not even with a lot of of force, because the O-ring woud 'catch' on the edge of the bore).

The pins now look like these pins:

https://www.google.com.au/imgres?imgurl=http://i892.photobucket.com/albums/ac129/md_auto/9A2AC0B3-ED23-45F2-A4E5-2B2C3616E8F1-1519-000001B17B517421_zps0b6bafd7.jpg&imgrefurl=https://forum.lowyat.net/topic/2923257/+220&docid=HDWts2us5Jk_sM&tbnid=KZ1yz_UIMwicUM:&vet=10ahUKEwj_272V4onfAhUDTI8KHUcqCXwQMwhOKAswCw..i&w=1024&h=768&bih=726&biw=1344&q=myvi brake pins kok&ved=0ahUKEwj_272V4onfAhUDTI8KHUcqCXwQMwhOKAswCw&iact=mrc&uact=8

Note that the O-rings on my pins don't protrude as far from the pin OD as the ones in the linked image do.

So now each caliper has one pin with an expanded insert (tighter fit in the bore), and one with four O-rings fitted. Both pins will smoothly slide in and out with some force manually applied, but are not 'free' to slide with no resistance, there is some significant friction. The caliper body is now quite firmly located and cannot be easily 'wobbled' by hand.

To recap; Previously, with un-molested stock pins, the caliper body could be manually wobbled very easily to a substantial degree, and pedal travel was quite excessive, and inconsistent.

Experiment 1:
Replacing the 'insert pin' (so that each caliper had two 'all steel' insertless pins) improved this significantly. Wobble was lessened and pedal travel / consistency improved. In both cases the caliper 'wobble' was largely associated with the pins moving in / out but in opposite directions, i.e. as the upper pin moved in the lower pin moved out, and vice versa. Replacing the insert pin with an insertless pin improved this, but didn't eliminate it.

Experiment 2:
Swapping two of the all steel pins back to orginal 'insert pins' (i.e. one insert pin in each caliper), but in which the inserts had been expanded (by wrapping shim foil between the pin and the insert) improved this more. The expanded insert pin was resistant to moving in / out, all such movement now occuring at the all steel pin only. Pedal motion and consistency improved compared to both the unmodified stock pins and compared to fitting 'all steel' insertless pins (ie. all pins).

Experiment 3:
Now, each caliper has an expanded insert on the 'insert pin', and a modified 'all steel' pin with four O-rings (as above). With the pads removed, the caliper body can be manually pushed in / out with some force, but isn't 'free'. 'Wobble' is very much reduced.

On the road the pedal travel is very significantly improved, less travel and more consistent than stock or with experiments 1 or 2. Some free travel still exists, which I am attributing to piston retraction associated with the seals (with both rear and front calipers).

However the pedal 'comes up' very easily and consistently with one 'tap' on the pedal, and the pedal is then firm and confidence inspiring. Heel / toe is easy and consistent, so long as the pedal has been 'tapped'. In general, pedal feel is improved / good and travel reduced even without 'tapping' the pedal.

Jacking the rear wheels off the ground and spinning the wheels, the wheels rotate easily, about the same as they do with no modifications to the pins. But, it is obvious that at least one pad at each caliper is in some contact with the disc. It can be heard and subtley felt as the wheel is rotated. The contact is light, and I don't expect it to cause any issues.

I'm fairly confident that the rubbing pads are more likley to be the the outer pads. The caliper body doesn't move freely because of the tighter fit between the pins and the pin bores, so the caliper body tends to remain in the same position when piston stops exerting force. The outer pads don't move as the brakes are released, other than to a very small degree as the clamping force is released, leaving them in very close proximity to the discs (but without any significant force pushing them against the discs). However, the pistons will still be retracted by the piston seals, so when the brakes are released a small gap will appear between the pistons and the inner pads. The inner pads will then be free to 'rattle' slightly away from the discs, or just to very lightly 'kiss' against them.

All in all, I'm very pleased with the improvement, night and day compared to how it was with the untouched stock pins. There is still some room for improvement, the piston retraction is still an issue (probably), but might prove difficult to address. A 10lb residual pressure valve would probably cause too much brake drag, a 2lb RPV may not be strong enough to prevent retraction. Still, a 2lb valve might at least reduce the retraction...

Regards,
John.
Great job and thanks for report!
Do you plan to install 2lb RPV?
 

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There is still some room for improvement, the piston retraction is still an issue (probably), but might prove difficult to address. A 10lb residual pressure valve would probably cause too much brake drag, a 2lb RPV may not be strong enough to prevent retraction. Still, a 2lb valve might at least reduce the retraction...

Regards,
John.
If you rigged up a means of pressurising the brake fluid reservoir you could find the optimum pressure by experiment. I can’t see it affecting the abs (or clutch more than marginally if it shares the reservoir) but I haven’t tried it so a suggestion only!
 

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Discussion Starter #37
I might try fitting a residual pressure valve at some stage, but I might not. I'm pretty happy with how the brakes are working now, so whether pursuing the remaining free play is worth the hassle...

I agree that it should be be possible to ascertain how much is too much residual pressure, by pressurising the reservoir (which is normally vented to atmosphere specifically to preclude the possibility of the system 'self pressurising'). I already have a home made 'pressure bleeder' which could be the basis of such a test. This is simply a cap (from an oil container) which just happens to fit the fluid reservoir orifice. I drilled a hole in this cap, into which I fitted a metal spigot tube, giving access to the interior of the reservoir with the cap on. The tube is soldered into a drilled through bolt (drilled lengthwise), the bolt is attached to the cap with two nuts, one each side of the cap (and sealed wih soft washers). The other end of the tube has the brass part of a Schraeder valve soldered onto it (i.e. a tyre valve with the rubber burned off and the valve itself removed). The reservoir is then pressurised with a simple tyre pump while bleeding the brakes or clutch (works well).

It should be easy enough to add a pressure guage to this set up. So to test pressure, I'd gradually pump up the reservoir while I rotated a wheel, noting the pressure at which the wheel started to become resistant to being rotated. It would be possible to put 10lbs pressure into the system (simulating the nominal pressure of the 10lb RPVs) and see whether any of the wheels became too 'draggy'. It wouldn't really be possible to test the effectiveness of a 2lb RPV (for lessening pad retraction), only whether a 10lb RPV created too much residual pressure.

Sure, it would be possible to put 2lbs in the reservoir and take the car for a drive, but the pressure wouldn't be stable in use due to heat expansion of the brake fluid. Driving a car when pressure can't escape from the system can lead to the brakes 'locking on' as the fluid expands (can = probably will). This is why there must be a small amount of 'free play' between the pedal, push rod, and MC piston. I once adjusted a pedal to zero free play, which quickly resulted in the rear brakes dragging very severely. With zero free play at the pedal, the fluid in the rear lines couldn't escape into the MC, so as the fluid heated up the pressure in the rear lines rose and rose until the pads were being quite forcefully pushed against the discs. My theory is that when there was no free play at the pedal the orifice in the MC bore (that leads to the rear brakes) was blocked by the edge of the piston seal (which in theory makes little sense since play was zero, not negative, but the only explanation I could think of...).

My home made pressure bleeder works well enough for bleeding the brakes and clutch, but the oil bottle cap isn't a perfect fit and leaks a bit, so pressure won't steadily 'hold' at a given psi. To use it for holding a constant pressure in the system I'd need a better fiting cap, so I'd need to source a 'real' cap and modify that to fit the bleeder tube (it's just a hassle to source a cap...).

Back to the current experiment. At low speed I noticed a 'groan' from the rear brakes. Jacking the car up both rear wheels rotate easily by hand, but the right rear pads are emitting a noise, obviously associated with pad / disc contact (even though the contact appears to be only fairly light). Poking around I discovered that the right side handbrake cable was sticky, and as a result the right side handbrake was not fully releasing when the lever was released (though very effective otherwise). I need to order a new cable (actually both), because the rubber dust excluding boots are perished and dirt has been getting in (hence the right side cable not moving freely). In the meantime I've cleaned the crap out and the cable is moving freely as it should, the handbrake is fully releasing (for now...).

Just why this sticky handbrake cable didn't seem to cause a problem until after I tightened the manner in which the caliper body is mounted I don't exactly know. I haven't yet driven the car since cleaning the cable, so I don't yet know whether the 'groaning' will have disappeared. If not, then I might have to reduce the friction in the caliper pins, by removing one or two of the the O-rings on the 'insertless' pins, and / or lessening the amount of shim between the rubber insert and the shank of the 'insert pins'.

Regards,
John.
 

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Discussion Starter #38
Update for anyone still interested in the ongoing saga:

Freeing up the sticky cable hasn’t eliminated the pad ‘groan’. I didn’t really expect that it would, because even with the caliper lever not fully released and so not quite resting against its’ stop, the brake wasn’t significantly dragging when manually rotated.

Looking elsewhere, I then took the caliper body off and had a look at the pin motion (in / out sliding). The ‘insert pins’ (with the expanded rubber inserts) still moved as they did when installed, i.e. smoothly with some moderate axial force applied. However, the pins fitted with O-rings had become seized. I couldn’t move them manually, had to give them a firm tap with a hammer, which freed them. Once ‘broken free’ they slid smoothly in / out as when first fitted, and much like the ‘insert pins’ now do but a bit stiffer (i.e. somewhat more friction between the O-rings / bore than between the rubber inserts and bore, but still able to be moved).

So, the ‘O-ring pin’ in each rear caliper pin was becoming seized in use, even though they moved OK when first installed (albeit requiring more force to move them than the ‘insert pins’). When the brake was cold the disc rotated quite freely but with some slight outer pad rubbing (it is the outer pad that is rubbing against the disc, the inner pad isn’t because of piston retraction). As the outer pad warms up it expands, and seems to be becoming very slightly thicker. This appears to be closing up any very slight running clearance between the outer pad and the disc, so the warm / hot pad rubs significantly on the disc, and it then gets hotter, expands more, etc. Because there is a seized pin, the caliper body can’t move enough to accommodate this.

The disc rotation doesn’t get ‘tight’, but it does become noticeably less ‘free’ as the brake temperature rises. The wheel still manually rotates fairly easily, but it seems enough drag exists to cause the pads to become a bit noisy (but not when cold, only with some heat). This seems to be the result of the ‘O-ring pins’ becoming seized.

To reduce pin friction / stiffness (when not seized) I removed one O-ring from each pin. Each ‘O-ring pin’ now has three rather than four O-rings. The ‘O-ring pins’ now slide more easily and with a similar resistance as the ‘insert pins’ do (i.e. a moderate force needed to slide the pins). I don’t yet know if this will stop them from seizing, or if it does for how long. I slathered in more ‘rubber grease’, but I’m suspecting the lube itself may be the problem more than the O-rings, so I’ll have a look for something more suitable than a plain ‘rubber grease’. I think Bendix sells something that might be better, and also rubber compatible (probably not the only product).

It’s a bit of a mystery as to why the expanded rubber inserts are not seizing while the rubber O-rings are. Both the expanded rubber inserts and the rubber O-rings are 0.25mm larger than the bore ID (as fitted to their pins), so have to be ‘squeezed’ to much the same degree to fit into the bores. If changing the grease doesn’t prevent the O-rings from becoming seized in use, I’m toying with the idea of machining the all steel pins undersize for part of their length, in order to fit ‘stock’ rubber inserts to all of the pins.

Anyway, after ‘un-seizing’ the O-ring pins, and reducing the pins’ sliding stiffness by reducing the number of O-rings, the pad / disc ‘groan’ has substantially lessened. I can hear it only very occasionally and momentarily when the brakes are not applied. On the other hand, as the brakes are applied there is a ‘groan’ as the brakes initially engage with a light piston force acting on the outer pads. This is only momentary and intermittent, the groan doesn’t happen with every brake application and when it does it disappears almost immediately as the piston force increases.

The ‘groan’ seems only to occur within a rather limited range of pad to disc force, i.e. with a very slight rubbing contact it doesn’t happen, with a slightly heavier contact it does, then with only a moderately heavier contact it stops. When the O-ring pins were seized it was occurring with the wheels jacked and rotated manually, more so when the brakes were warm. After the pins were ‘un-seized’ and sliding friction reduced, it doesn’t occur when the wheel is manually rotated, cold or hot.

With the reduced axial pin stiffness, the brake action and pedal feel is just as good (i.e. removing one out of four O-rings on each pin has made no difference to pedal ‘free play’ or feel). I think that the sweet spot is to have just enough axial pin friction / sliding stiffness as needed to stop the caliper body from easily wobbling and moving outward on the pins. Any more may cause an issue.

Regards,
John.
 
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