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Brake Fluid

what does the DOT rating mean on brake fluid?
does the higher the DOT rating have a higher boiling(resistance) point? I am currently running Castrol Response DOT 4 in my GTV
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Re: Brake Fluid

dot rating does refer to boiling point rating, most modern cars require dot 4 nowadays, nobody much uses/sells dot 3 now. don't be tempted to get the dot 5.1 as used in motorsport , it will attack the rubber in the hoses/master cylinder/calipers etc make sure you get a decent quality fluid also as not all dot4 fluids are rated at the same boiling point, although not sure if they all state the boiling point on the containers lucas stuff we use boils at around 230c , old fluid should be changed if it drops down to around 180c. should be done every 2 or 3 years as it does age by absorbing moisture thereby weakening it down and lowering the boiling point. this happens more if you are hard on the car by doing repeated high speed braking such as at track days, also if you sit at the lights with your foot on the brake after a decent bit of braking it is possible to boil the fluid in the calipers as you sit there, only to find that out next time you press the pedal and it goes to the floor
 
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Re: Brake Fluid

A couple of brake fluid points: Brake fluid absorbs water over time and so boiling point is reduced, hence the need to change fluid every couple of years or so. Brake fluid also has a low ignition point, drip petrol onto a hot exhaust and it boils, drip brake fluid and you have a fire. Be warned!

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Re: Brake Fluid

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A couple of brake fluid points: Brake fluid absorbs water over time and so boiling point is reduced, hence the need to change fluid every couple of years or so. Brake fluid also has a low ignition point, drip petrol onto a hot exhaust and it boils, drip brake fluid and you have a fire. Be warned!

Dan
also makes an excellent paint stripper so be careful
 
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Re: Brake Fluid

Department of Transport rated 4 is what I use, but have had 5.1 with no noticeable difference. Steady old driver.
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Re: Brake Fluid

Dot 4 in everyday cars changed at required interval.

I use silicone based in our old cars for 2 reasons. It doesn't take in water so has consistent performance without need for regular changes. It doesn't attack the cellulose paint if you spill a drop on the body or under the bonnet.There's always lots of talk about spongey pedals etc but I've never noticed it on our cars.

BTW modern 2 pack paints resist brake fluid very well not that I recommend any experiments!
 
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Re: Brake Fluid

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Originally Posted by alfafamily View Post

BTW modern 2 pack paints resist brake fluid very well not that I recommend any experiments!
can i go try that out at the local bmw dealership i will wait until it's dark
 
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Re: Brake Fluid

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can i go try that out at the local bmw dealership i will wait until it's dark
Good idea Kev,let us know how you get on(make sure you take some nitromors as well just in case I'm right)
 
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Re: Brake Fluid

bit out of my league here but here goes
i thought
dot 4 is usually all you will need for normal use that
dot 5.1 is used for higher performance and does need more regular changeing as it is more absorbent.

i THINK dot 5 is the one you should not mix and perishes certain types of rubber.

back in my comfort zone whilst you can drop some and wipe it off quickly and be lucky to get away without it "eating into the paint "
i would not recomend you try it on any type of paint.
am sure someone will be along shortly to fill in the technical gaps

Last edited by dnf; 09-01-08 at 22:11.
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Re: Brake Fluid

DOT 5 is what you definitely do not want to use for modern Alfas!
..unless of course your brake system was designed specifically to be used with it, typically historically this would be the case for some older cars that needed high boiling point fluid.

Everything you ever wanted to know about brake fluid in a superb article:

StopTech : Balanced Brake Upgrades


DOT 5.1 is perfectly safe, it is essentially a high spec DOT 4 that meets DOT 5 performance requirements (but without nasty silicone content used in DOT 5 fluids that may ruin your brake sytem).

Racing DOT 4 fluids can often have higher boiling points than DOT 5.1fluids, the DOT boiling point specs are just minimums, and there are lots of other characteristics that a brake fluid has to meet before it can be labelled a DOT5.1.
Most racing DOT 4's would fall into this category.

Cheers,
TB

I'm not a doctor - but I really do recommend braking later
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Re: Brake Fluid

I am on a Motul F600 dot 4 racing fluid
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Re: Brake Fluid

This one is sort of well, a been here often, Eh? Gazza? No problem, but well discussed on backposts.:
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Re: Brake Fluid

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Originally Posted by Trailbraker View Post
DOT 5 is what you definitely do not want to use for modern Alfas!
..unless of course your brake system was designed specifically to be used with it, typically historically this would be the case for some older cars that needed high boiling point fluid.

Everything you ever wanted to know about brake fluid in a superb article:

StopTech : Balanced Brake Upgrades


DOT 5.1 is perfectly safe, it is essentially a high spec DOT 4 that meets DOT 5 performance requirements (but without nasty silicone content used in DOT 5 fluids that may ruin your brake sytem).

Racing DOT 4 fluids can often have higher boiling points than DOT 5.1fluids, the DOT boiling point specs are just minimums, and there are lots of other characteristics that a brake fluid has to meet before it can be labelled a DOT5.1.
Most racing DOT 4's would fall into this category.

Cheers,
TB
tis what i said
but written in English
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Re: Brake Fluid

Aye! DOT4 is DOT4,

DOT5.1 is a better version of DOT4.

DOT5 (cf DOT5.1) is the synthetic one that does not absord moisture (but also does not lubricate the seals, which some systems actually need) and any water that does get in, is not absorbed, so collects in one place and rusts your brake like from the inside. Only good for frequent-change applications, like motorsport.

DOT4 changed every year is better than DOT5.1 changed never.


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Re: Brake Fluid

if you mix dot5 and dot4 your braking system gets clogged with silicone residue, as a friend of mine found out
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Re: Brake Fluid

As ZF says this a bit of an old debate but still worth a re run I reckon.
I don't think anyone has expressed a different opinion yet, they've just said the same thing in different ways. The only thing I would add is not to confuse Dot 5 and Dot 5.1. Dot 5.1 is not silicone based fluid and should still be changed at the correct intervals. Dot 5 is silicone based and is often recommended for older brake systems where compressibilty is not an issue(eg. in ABS systems). As I said before I use Dot 5 in classic cars because of its long life properties and its safety with regard to paint damage. For me water ingress to the system is not a major issue because my car rarely gets wet and is only lightly washed once a year.
Different kinds of use obviously throw up their own problems but if in doubt use Dot 4 or 5.1 and change at the proper interval and everything should be ok.
 
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Re: Brake Fluid

Agree with AF, stick to those suggestions, and you will be on the right road/track?:
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Re: Brake Fluid

I was just going to top up the level after changing the clutch slave cylinder but i cant find Castrol Response anywhere and it was Oct 2006 the fluid was changed.
thanks chaps
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