Which Brake Fluid

[topwelshman]

What sort of brake fluid should I be using? I race a BMW 325 in the Kumho Championship which uses Mintex 1155's and standard discs which I'm condidering upgrading as well

[Morris 1100]

Brand names are not important. Just use a good brand of DOT 5 Grade fluid (most of them are) and change it often.
When you bleed your brakes the fluid that come out should be the the same colour as what went in. If the fluid comes out darker it is being overheated and should have been changed long ago.

[Tim Falce]

Hmmmmmmm, good one that. Castrol SRF is about the best but at £40 per litre very expensive. I have been using it for a while and it is good although I have gone back to Halfords dot 5.1 which i find is excellent as well.

[topwelshman]

Ok, will find some dot 5 stuff

[Tim Falce]

Be carefull, SRF and dot 5 are synthetic, dot 5.1 is not. Just depends on what you can and can't put in your car

[JohnMiller]

Dot 5.1 can be mixed with the like of Dot 4 too. Dot 5 can't I believe.

[topwelshman]

Ok, so what's the difference between dot 5 and dot 5.1, is hte 5.1 higher grade?

[Tim Falce]

Not sure on the temp rating although I believe the dry boiling temp of 5.1 is superior to dot 5. On reading up on fluids I have found that with synthetic it doesn't absorb water so the wet boiling temp stays high for longer, the down side is that if any moisture gets in the system it stays as bubbles of water then boils and turns to gas thus giving a spongy pedal. Also synthetic is supposedly compressable which isbnt good for racing. The non-synthetic absorbs water so you don’t get this problem but you would need to change it more often for racing as the wet boiling temp will drop quicker. In a road car this isn’t really a problem.
Synthetic is not recommended for racing.
I will stand to be corrected if anyone knows better.

[topwelshman]

Ok, so I need dot 5.1 Non synthetic oil, right?

[thebear]

Originally posted by topwelshman
Ok, so I need dot 5.1 Non synthetic oil, right?

Right. The water is absorbed from the atmosphere and can not be removed by any convenient means. Also, don't forget to dispose of the old stuff in an enviornmentally friendly way. :confused: There should be some collection means at any racing facility or shop that services race cars.

[Tim Falce]

Originally posted by thebear
Right. The water is absorbed from the atmosphere and can not be removed by any convenient means. Also, don't forget to dispose of the old stuff in an enviornmentally friendly way. :confused: There should be some collection means at any racing facility or shop that services race cars.

Or down the drain

[Tim Falce]

Originally posted by topwelshman
Ok, so I need dot 5.1 Non synthetic oil, right?

I think that has to be your choice based on what facts you want to believe. I know lots of people that will only use Castrol SRF (Synthetic Racing Fluid). Whatever you use make sure you flush all the old stuff out first.
How much does your car weigh?

[autosportfan]

DO NOT USE DOT 5. This is a Silicon based brake fluid, which generally gives a spongy pedal feel. The main reason is that silicon has a low surface energy, meaning air bubbles are more stable than in standard ester type fluid. The only people using DOT 5 as standard are the military (because the fluid does not take in moisture meaning vehicles can be stored for a long time without degradation of the fluid) and Harley Davidson. DOT 5 is old technology and was produced because the silicon base fluid had a higher boiling point than the old type DOT 4. Recently, Super DOT 4, also called DOT 5.1 have been developed, which is basically easter based, but with a boiling simliar to DOT 5. Castrol SRF is a special type of Super DOT 4, a silicon ester (v. expensive to manufacture), which is compatible with DOT 3, 4 etc, but not the disadvantage of spongy feel.
It should be noted that boling point is not the only property that dictates the DOT grading, others such as low temp viscosity is also considered. There are some brake fluids have a DOT 3 grading, but have a boiling point similar to DOT 5.

[topwelshman]

The car weighs about 1150 kg and after chatting to my mechanic I think we're going witht the Castrol SRF, not going to mess about for a few £.

cheers everyone

[graham bahr]

forget the rest of the bull, the thing you should really be compairing with brake fluid is the boiling point.
for what its worth my car boiled justabout all manor of different normal dot type road fluids, i now only use AP600 racing fliud and never have a problem any more, for safety sake when you change fluids flush out the old stuff and DONT mix different fluids, also remember that race fluid is more hydroscopic than road fluid and needs regulary changing.

[noodles]

graham,

I think you mean hygroscopic.

Nontheless, you are correct. My view has always been that if you are racing, use a racing spec product.

Therefore, go with a product such as AP Racing.

[topwelshman]

Ok cheers again all

[Tim Falce]

Originally posted by graham bahr
forget the rest of the bull, the thing you should really be compairing with brake fluid is the boiling point.
for what its worth my car boiled justabout all manor of different normal dot type road fluids, i now only use AP600 racing fliud and never have a problem any more, for safety sake when you change fluids flush out the old stuff and DONT mix different fluids, also remember that race fluid is more hydroscopic than road fluid and needs regulary changing.

Graham, you don't need brakes, your engine doesn't go

[graham bahr]

dont you know its cruel to mock the afflicted?

dont worry my engine will be back and better than ever, maybe 3 seasons on the same set of bigends was a bit much though.

[graham bahr]

i suppose if all else fails on the brakes front, you could always use someone elses? if you see what i mean