[konrad96]

Guys,

need help with this before I set fire to this damn car!!! She's a 1996 ph 1 spider. The brake compensator valve sprung a leak (and was rusted pretty much solid) so I have replace it. With the brake system in pieces, I took the opportunity to replace the master cylinder, too. The compensator is a genuine part, the brake cylinder a name brand, so I have confidence the parts are sound.

I've bleed the brakes through ad infinitum but still have a long brake travel before the car really stops - but only going forward! When I'm reversing, the brakes will stop the car almost instantly. What I need to do is get the same brake feel when I'm moving forward.

It seems to me that this must be down to the compensator valve and how I've adjusted it. Brake pressure must be fine, or I wouldn't be stopping so well in reverse. Likewise the friction surfaces. The effective braking in reverse suggests that the position of the compensator must be allowing more pressure to the rear brakes than it should.

Problem I have is that the manual requires the vehicle to be on its wheels, with a driver in the drivers seat, and then the 4.5kg/10lb pull downwards on the compensator valve lever to set the thing. I have to rely on getting the car on axle stands, so the wheels are hanging, which obviously will move the ARB, which will affect the load on the compensator in some way.

I know I need to adjust this, either putting more pressure on the compensator spring, and thus (I think) closing off the pressure to the rear brakes a little, and thereby increasing efficiency of the front brakes. I'm trying to avoid trial and error - i.e. up on the stands, adjust, down off the stands, quick test, back up again, etc etc.

I can't believe this hasn't come up before, but I can't find any real info on the actual adjustment in other posts. Anyone any ideas on how to properly adjust this thing? http://www.alfaowner.com/Forum/images/smilies/banghead.gif
:banghead:

 

[spankdanny]

The compensator has no effect on the front brakes it is in the rear brake system only. Sounds like air still in system. Only way I found to bleed it was the old two man system. To adjust I guess you need 4 car ramps.

 

[konrad96]

If there was air in the system I wouldn't have a really good pedal when reversing. The compensator will be totally open when braking in reverse, thus ensuring maximum flow to the rear calipers. When the inertial forces are heading forwards, the idea is that the compensator closes partially, thus reducing flow to the rear brakes and preventing lock up and the resultant vehicle spin. I think the problem now is that the braking effort is probably slightly biased towards the rear, whereas it should be biased towards the front. It's how to adjust the valve properly that's the issue.
Also I've put almost two litres of DOT 4 through the system to make sure it's clean, so I'm confident there's no air in there.

 

[pkr]

You did the brake M/C, so did you do the other bleeding sequence?

See workshop manual vol 1 S33 p7 ( "Recovery in the case of air in the piston " ) where it gives the alternative sequence ( right rear, LR, LF, RF ) which you should do before going round in the correct sequence ( LF, RF, LR, RR ). Note the sequence there. You may have inadvertently got part way through so the rears are now OK but the fronts are still full of air.

Where they say pump the pedal repeatedly, I believe they also mean rapidly - not like normal bleeding. When I did it, I'd pump the pedal about 8 times, then paused to top up the reservoir. Just to be certain, I'd do the 8 pumps twice per wheel before moving to the next wheel and repeating. Then when I'd done that on all 4 wheels, I did it again before moving on to normal bleeding.

Try that.

 

[konrad96]

I always use fast pumps like that when replacing a master cylinder. In fact, I used a pressure system to get the fluid into the cylinder to begin with, then used fast pumping in that order, starting LR, then the normal type bleeding all round, starting LF. I'm getting clean air free fluid from each caliber. That said, I'm no expert! The first tranche of bleeding actually produced very milky fluid from the calipers, like foamy almost - don't know what caused that. But all fluid coming out is clean now and since the foam there's been 1 litre through the system, roughly a quarter through each corner.

hope I'm not coming across as bolshie, I'm grateful for any suggestions!

 

[sraouf]

The "foamy fluid" you refer to to is just a symptom of tiny air bubbles in the system so I wouldn't worry too much

 

[spankdanny]

No bolshieness detected. As you say the compensator reduces pressure to the rear callipers, but doesn't reduce pressure to the fronts that would be dangerous. With the engine off is the brake pedal rock hard. As in you can't press it down more than an inch. If it sinks down then there is air in the system or m/ c faulty. Air in the ABS is possible which is a whole new can of worms.

 

[konrad96]

with the engine off I can maybe press the pedal an inch, but no more. I've had other cars where the pedal went absolutely rock hard, but I've never had that in either of my Alfas. What is really flummoxing me is the reverse situation: with the car in reverse, I touch the brakes and it stops instantly. Perfect pedal response. Exactly what you want. Into first, and moving forward, there's a long pedal travel. It eventually stops pretty well, but the pedal has to go much farther during forward movement than it does during rearward movement if that makes sense. Surely if there was air in the system, the spongy pedal syndrome would be apparent no matter what direction the car was travelling?

 

[spankdanny]

Your right doesn't sound like any air in the system. Front callipers alright? What were the brakes like before the problem?

 

[konrad96]

when I got the car the brake disks and pads had been recently replaced. The adjuster on the existing compensator was rusted solid. Brake pressure wasn't great - but before the MOT I adjusted the compensator by moving the anchor for the spring on the ARB forward slightly, putting more pressure on the lever arm. this got the stopping power up to where it passed the MOT without difficulty - 63%, whilst not perfect, well over the 50% pass mark.

I just adjusted the new compensator again - using 15lb of a weight on the arm, instead of 10lb. I wanted to see if this would in some way compensate for the fact that the car wasn't sitting on the axles. Just took it out for a drive and the brake effect is much improved. Can't exactly say it stops on a sixpence, but it's a hell of a lot better. I'll try again later, maybe with 20b weight (double the recommended weight in the manual) to see what happens.

i'm wondering if the new disks and pads were possibly cheap ones. I have heard that cheap friction surfaces can have a real impact on stopping ability. Anyone had any experience of this?

ANyway, looks like the problem is definitely related to the compensator valve adjustment.

 

[spankdanny]

Mine failed MOT on rear service brakes but hand brake passed and fronts passed too. The compensator was stuck reducing pressure to the rears. My type of compensator is no longer available so I made up some brake pipes and bypassed it. Passed MOT but I can feel the ABS kicking in earlier. I found a used one now but haven't fitted it yet.

 

[konrad96]

They seem to be a right pain in the ass, these compensators. Probably fine when they're working. I take it yours is the ph2 one without the spring? I saw those for sale new on maybe Autolusso's site, recently, around £150. Oddly, I discovered today that the ph 1 compensator appears to be identical to that used on the iveco daily 35s - go figure. not any cheaper, though.

 

[spankdanny]

Your right. EB Spares have got them back in stock. £190. Ouch. Hope this used one is good.