Disk brake options

[Roger King]

Bigg Red offer a good thermal coating which gives an excellent hard wearing finish. Yellow passivate is correct for the cast iron calipers.
It's practically impossible to keep fluid off them, I find - the bleed nipple usually points upwards, and always has a 'nipple full' (ooer missus) of fluid left in it, unless you poke it clean with a tissue.

Reading this through, I'm not sure I should post it...

Whatever you do, don't be tempted by silicone fluid.

[Paul Blore]

Whatever you do, don't be tempted by silicone fluid.

Agreed. I use DOT 5.1.

[amulheirn]

Thanks everyone... I think I'll go for the Wilwood ones, pending the next pay packet.
What's bad about silicone? Just not as effective?

[Roger King]

I used to use it in my classics, but after the third time it left me with no brakes having boiled in road use (not track), it scared me so much I went back to DOT4. Very nearly wiped out a friend's 300SL Gullwing - gulp!

[David Large]

I used silicone brake fluid in my car for the best chunk of 20 years with no problems at all, When we substantially modified the brake system, changing the back brakes from drums to discs, putting bigger disc and calipers on the front and a split circuit master cylinder, then because of all the bad press silicon brake fluid had been getting I went back to dot 4.

David

[Paul Blore]

I've used DOT 5 in the past and could never get a consistent feel to the pedal. Some days it would be firm and other days it would be spongy. The reason is that silicon is compressible, which isn't generally a good thing when it comes to braking systems.

DOT 5.1 is a poly glycol based fluid that has all the high temperature benefits of DOT 5, but without the downsides of silicon.

Roger,
It wouldn't have been the DOT 5 fluid that boiled, but the water that was sitting somewhere in the system. Silicon fluid doesn't absorb moisture like poly glycol based fluids, which on the face of it sounds like a good thing. The problem is that any moisture in the system will eventually pool together at a low point in the system and this can boil, with disastrous effects on braking performance. Even if it doesn't boil, it can eventually cause corrosion.

Paul

[Roger King]

Not sure about that as the first time was in a brand new system after just two weeks, so I wouldn't have thought there was time for a significant amount of water to form. Following these episodes, the brakes returned enough to drive home carefully but were very different from before - the fluid never recovered. I had to flush and refill on each occasion. As you found, the pedal feel was also inconsistent.

[CobStang]

Super DOT 4 is the way to go, higher boiling point than 5.1, compatible and cheap as chips.
Have never managed to boil the stuff, and I've tried !

[Paul Blore]

If you managed to boil the silicon fluid Roger, you were either trying far too hard or something was amiss somewhere.

DOT 4 fluid would have boiled much sooner. That aside, there are too many inconsistencies with DOT 5 fluid that out weigh any potential benefits.
I'd not come across Super DOT 4 before, but it looks to be worth investigating. However, it is recommended for racing so I may question the longevity as racing brake systems typically get far more maintenance that those of road cars.

Paul

[Paul Blore]

Having done some reading up on Super DOT 4, it appears to be a suitable alternative to all other brake fluids a parts from the obvious DOT 5.1.
That being the case, if Super DOT 4 is so good and comparable price wise, why are all the other types still available?

It's like Intel still selling 386, 486 etc. processors when the latest and greatest is on the shelf.

Paul