Brake Fluids

[WideOpenThrottle]

So, if brake fluid absorbs water then why can't you use transmision or power-steering fluid instead?
After all they are all hydraulic fluids!
Is it something to do with the seals leaking fluid onto the brake pads? Or the oil perishing the seals?
Anyone in the know?

[Stevo]

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[Habanero666]

There are a few exceptions however, Jaguar, citroen and some Range rover products use a mineral hydraulic fluid for braking systems.

The Citroens have a system that uses green mineral oil (LHM) for the brakes and hydro-pneumatique suspension circuits! viva la france!!

Anyway you can find it all here: http://en.wikipedia.org/wiki/Brake_fluid

I recommend that if you are tempted to go high performance DO NOT use Dot 5 fluid, unless you renew all the components to use silicon type fluid. Mixing mineral hydraulic fluid with silicon fluid in the system means an expensive full rebuild and replacement job!

I recommend a synthetic type dot 4 brake fluid for all performance application due to its low hygroscopic and viscosity properties.

Let me know if you want this stuff.

[JiB]

I think the reason cars were not designed to take completely hydrophobic fluid is because if water ever enters the system it would create a dangerous situation.

"Bubbles" of water would form within the fluid instead of being assimilated. This means that if the system gets warm, there may be potential for brake loss when the MC tries to compress vapour/evaporated water when the brakes are applied. This easily compressable bubble absorbs the pressure from the MC instead of pushing the pistons in the calipers.

As for types of brake fluid, I use Penrite Sin in the race car with no fade problems. But for a road car, I haven't had problems with OEM or the Castrol stuff in the silver bottle.

Hope that helps.

[WideOpenThrottle]

So am i reading it right?
There are three types of brake fluids,Glycol-ether based,mineral & silicon.
the most common is Glycol which is what most cars use in NZ & what we commonly buy off the shelf.
If i put in a mineral or silicon oil then i have to completly flush &/or change the entire seals?
Maybe i shall stick to the regular stuff & change it more often.
Wonder how often we top-up & put in the wrong one?

[Mark]

The OEM specified fluid (for my NB) is DOT 3.

Buy the cheapest fluid from Supercheap Auto etc, Just check it meets the correct DOT rating. Dot 4 fluid might be "better" in that it's got slightly higher wet and dry boiling points.

Here's the DOT specs, and apart from boiling point and viscosity spec, DOT 3 and 4 seem to have identical specs.
http://www.fmcsa.dot.gov/rules-regulati ... on=571.116

IMO there's a lot of myth and snake-oil salesmen out there with fluids for cars. That includes motor oils. I never saw any data for bench test results - running engines to destruction on various duty cycles, to prove that brand X is better than type Y. Yet that's a standard method used on fuel and oil additives. That they'd rather sell the stuff on anecdotes and celebrity endorsement methods the same way that anti-aging face cream is sold should tell us something.

[dino3]

Just to add there is also Dot 5.1 (not to be mixed up with Dot 5) that can
be mixed with Dot 3 and Dot 4 but not with Dot 5.I think it is a synthetic
and has a higher boiling point than 3 & 4. Dot 5, silicon ,is mainly used
in Harleys (factory) and by Rodders (no paint damage) or in competion
(higher boiling point)and by the US Army and should not be mixed with
anything else. I have just replace a master cylinder (NA) as it was leaking
.On checking all 3 cars they all were the same ,paint peeling on the booster
beneith the cylinder ! On removing the master cylinder it appears to be fine
but the washer under the resovouir is leaking and running
underneth...something folks may want to check ,it makes a mess of the paint!