Brake Fluid

[Melvin W.]

Re: Brake Fluid

If I knew that, they wouldn't be leaking.

Latest time around I honed them, cleaned them again, sealed the internal edge per the service manual and the owner reports them eventually leaking. It comes back here soon, so I'll have to again see what looks out of place or what might be leaking. There was nothing obvious the first time I had it or with the re-do, which happened before it left here.

I've re-sealed DOT3 cars previously, so it is a mystery...

Did you check for rotor run out causing the calipers to leak?

[Larry M.]

Re: Brake Fluid

Duke,

I'm close to putting brake fluids into my 69 after restoration. All the hoses and lines are new, as is the MC (which BTW came with a DOT 5 recommendation) but the calipers are lonestar rebuilds with SS sleeves and O-rings. Do I really have to disassemble the calipers and clean them prior to installing the DOT 5? Why??? It would mean the removal of all calipers from the car. Please advise.

Mike

If Lonestar rebuilt your calipers, using DOT 5 fluid will void your warranty. But if you want to give DOT 5 a go, then I would not do anything to the new/rebuilt components except to fill them and bleed them.

Lonestar did show one DOT 5 source that did not cause swelling of their components, so you could visit their website and check on this or call them.......knowing full well if they give you this source you are still on your own with no warranty.

I think we previously discussed (archives) a few DOT 5 manufacturers that SHOULD have fluid that was proven okay in the past and has not changed per manufacturer statement........but again you roll the dice if you use it.

I completely rebuilt my brake system back in 1994 and filled with DOT 5 from Stainless Steel Brakes in New York. They were the first to use SS liners and literally wrote the book on SS caliper rebuilding. Their book on this subject (again 1980's issue) recommended DOT 5 in the rebuilt system......and they sold this fluid. It is what I used back then.........and 25 years later this fluid is still in the system and no brake failures. I have only 1 quart of the original fluid left for topping off etc. So I may be fine yet for awhile.

But unless I could prove to myself 100% that silicone fluid worked with currently available brake rubber components, I would probably just use a good DOT 3/4 fluid in a new brake system and know that I will need to flush it every 5 years or so. The last thing anyone needs is to have a brake system failure at 70 MPH. The C2 parking brake will not help at this speed.......I have tried it under controlled conditions and it was not very helpful in stopping my car

Larry

[Duke W.]

Re: Brake Fluid

Duke,

I'm close to putting brake fluids into my 69 after restoration. All the hoses and lines are new, as is the MC (which BTW came with a DOT 5 recommendation) but the calipers are lonestar rebuilds with SS sleeves and O-rings. Do I really have to disassemble the calipers and clean them prior to installing the DOT 5? Why??? It would mean the removal of all calipers from the car. Please advise.

Mike

You don't have to, but I sure wouldn't proceed without removing, disassembling the calipers, clean with denatured alcohol, thoroughly dry and then reassemble with silicone fluid. New hoses should be flushed with alcohol, too because they are usually assembled with conventional brake fluid where the fittings are swagged to the hoses.

Also, the brake pipes should be flushed with alcohol and thoroughly dried with compressed air.

The objective is to get every last molecule of conventional brake fluid out of the system. I've just heard too many bad stories about mixing the two.

Duke

[Patrick H.]

Re: Brake Fluid

Did you check for rotor run out causing the calipers to leak?

This car sits in a showroom at the owner's dealership. It hasn't accumulated 100 yards since they were replaced the second time, and didn't move an inch before the first leaking episode. Runout has not been a factor.

[James G.]

Re: Brake Fluid

IF you pull a vacuum on the top of the MC with the system closed will it remove the trapped air bubbles in the fluid? If I am not mistaken this is how the factory filled the system.

[John D.]

Re: Brake Fluid

They may be immiscible but SAE paper 810804 from 1981 says having a mix of conventional brake fluid and silicon even at high concentrations yielded no adverse affects on elastomers or brake performance on vehicles tested. The paper supports no need for extensive disassembly and/or denatured alcohol flushing when changing to DOT 5.

I carefully flushed my brake system with DOT 5 almost 30 years ago with zero problems.

[John D.]

Re: Brake Fluid

IF you pull a vacuum on the top of the MC with the system closed will it remove the trapped air bubbles in the fluid? If I am not mistaken this is how the factory filled the system.

When i worked in GM assembly plants years ago the brake fluid (DOT3) was stored in large totes that were heated and the fluid was held under vacuum to boil off any moisture. The brake systems were evacuated, held at vacuum to check for leaks an then pressure filled. The system was tested using a special test head that mounted to the master cylinder that pumped up the system held it at high pressure to check for leaks and air entrapment. A very complex piece of equipment we tested the calibration on each and every shift.

I cant speak for back in the C2 days but one old old timer said the systems were filled by putting a fill head over the MC and flushing the conditioned brake fluid through each caliper (or drum)

[Terry M.]

Re: Brake Fluid

FWIW: When my C6 was built, October 2007, the brake fluid was still DOT 3 in a large tote. There was no sign of heaters or vacuum on the tote, but the system was evacuated and fluid added under pressure.
I found it interesting that the clutch hydraulic fluid was DOT 4.
I should have asked the engineers: "Why not DOT 4 for all of it?" although I suspect I know the answer.

[Timothy B.]

Re: Brake Fluid

I'm having the calipers rebuilt.

Len,

When I converted my 67 to dot 5 silicone fluid I cleaned the master cylinder as dry as possible without removing it. I then filled with dot 5 and started bleeding until everything ran the purple color of the dot 5 and have never had a problem.

I have had problems with the lip seals getting flat spots from extended non use and leaking so keep that in mind but that is a completely different problem than the dot 5 questions.

I ran it by George G before I did it and he told me that's how he did it also.

[Richard S.]

Re: Brake Fluid

No expert on silicone brake fluid,I do use it in my Mopar and Corvettes,however the one I do use stipulated compatible with SBR, EP, NEOPRENE,
and NATURAL RUBBER, plus it is made in the USA.