Brake Fluid

[Bod]

Have just purchased Dot 5 brake fluid for jag setup front and rear. Any negatives

[sambo]

None that I can think of aside from your bank balance.

[boxhead]

Make sure you flush out ALL of the old stuff.
Is teh DOT 5 silicone based? If so you do not want any of it mixing with the old fluid, this includes what may be in your rubber hoses, caliper seals, master cylinder seals etc.

[Dennis O'Shea]

Dot 5 is all I have ever used and have not had any issues

[Bob In Ct]

While it has very good high temperature qualities DOT 5 is not very tolerant of water (which is fine if you're changing it after every race). If not, the water which finds its way into the system may not be absorbed by the fluid and is then able to rust components. DOT3 is much better at absorbing water and therefore makes a much better fluid for daily drivers.

Bob

[JST4FUN]

I just changed mine this week using Valvoline Synthetic DOT 3&4. My research revealed DOT 3, 4 & 5.1 were my choices with each having both a higher dry and wet boiling point as the number increased. Also, DOT 5.0 is silicon based and not compatible with the other 3. In fact, my SPF manual recommended against using 5.0. I couldn't readily find 5.1 locally, so I used the highest boiling point product I could find here without ordering it.

[mreid]

DOT5 also absorbs air which makes it not the best option. You are always better off with DOT3/4/5.1.

[Bod]

Thanks all for the info. All parts are reconditioned or new. Now that I paid the moula I may as well use it

[bobcowan]

Lots of negatives to the 5, It is generally not recommended for street vehicles. Even Harley quit using it.

5 is silicone based, and all the others are glycol. Silicone is hydrophobic - meaning that it does not absorb water into solution. Which initially sounds good until you realize what that means. Water tends to pool, and is heavier than brake fluid. So the water ends up in the calipers. There's a number of good reasons we don't use water as brake fluid.

Glycol is hydrophyllic, and absorbs water into solution. You won't get the problems with corrosion and steam like you do with silicone. But that's the reason you need to flush it every so often.

Oddly enough, silicone fluid is slightly compressable. You end up with a mushy pedal.

The functional differance between the differant fluids (3,4,5,5.1) is dry and wet boiling points. Get DoT3 much above 350* or so and it turns to live steam. That's a bad thing. 5.1 is fairly new on the market. It has pretty much the same boiling points as 5, but it's glycol.

For street driving, 3 is just fine. If you want a little extra, spring for the 4. I use 4 in my street vehicles, because it makes me feel better.

If you're racing, you need to use some pretty good stuff, and flush often. Motul is pretty popular. I use Wilwood 600 - it's relativly inexpensive and easy to come by.

You CANNOT mix glycol and silicone. I will clot. Most brake systems are built using glycol fluid as a lube and for anti-corrosion. If you want to use silicone based, you need to disassemble everything, clean all the parts, and re-assemble with silicone.

In short, I recommend you sell that silicone DoT5 to some one who owns an old harley, and buy glycol based fluid instead.

[andronikos916]

I am thinking to bleed my brakes soon.

Backdraft manual recommends Dot 5 for brakes. It seems that Dot 5 is not the best. Is it any special with the Backdraft brakes that I am not aware?

So do you see any negatives of using the Dot4 - Motul RBF 600 on my brakes? I am using the same on the clutch and so far seems to be ok.

Thanx - Andronikos,

[bobcowan]

Originally Posted by andronikos916

So do you see any negatives of using the Dot4 - Motul RBF 600 on my brakes? I am using the same on the clutch and so far seems to be ok.

Thanx - Andronikos,

Other than cost, I can't see any down side to it.

[andronikos916]

Thanx bobcowan.