Brake fluid

[Gregory G.]

I am totally rebuilding my brakes. Rebuilt calipers with ss sleaves and o-ring seals as well as a new master cyl and hoses. I was wondering if I should change to silicone brake fluid. I have read positives and negatives. I guess the biggest negative I heard is that it is slightly compressable and could result in a slightly softer pedal. I also heard that it is harder to bleed. The positives are that it does not absorbe moisture and will not eat any paint.
Please respond with your experience if you tried silicond brake fluid.
What is the best method to flush any residual fluin in any of the old lines?:

[Daniel S.]

Re: Brake fluid

Greg,

I swithched over to silicone or Dot5 last year when I replaced my master cylinder, and have nothing negative to report.
The initial brake bleed was not fun, but when is it ever on Corvettes?
I do not think the difficult bleed was silicone fluid related at all.
I can not tell a difference in pedal feel between dot3/4 and dot5.

I just checked the level in the master cylinder the other day and it is as clear as the day I added it.
I have heard the denatured alcohol is good to flush old fluid out, however I did not use it myself.

Dan

[Duke W.]

Re: Brake fluid

If you've already assembled some components with conventional brake fluid, you're going to have to disassemble them, clean in denatured alcohol, and reassemble with DOT 5.

I recommend going with DOT 5 for complete rebuild, but you have to start with everything clean and dry. The hard lines can be flushed with denatured alcohol and dried with compressed air. Also, new flexible hoses should be used, but they should also be cleaned.

Duke

[Timothy B.]

Re: Brake fluid

Agree with Duke. That is what I did and my brakes work great! Flushing the lines is not hard to do at all and just use compressed air to dry them out.

[Joe L.]

Re: Brake fluid

Greg-----

After much experience and research, I consider that silicone DOT-5 fluid is the only way to go. All of the "problems" attributed to silicone fluid are, I believe, really problems generated by other things and NOT the fluid, itself. 1965-82 Corvette brake systems are VERY difficult to bleed. Period. The 68-72 are the most difficult, but I'll never understand why. Basically, there was little change in the brake systems during the 65-82 period.

I did some tests some time ago comparing the "aeration retention" properties of both DOT-3 glycol-based fluid and DOT-5 silicone-based fluid. There was absolutely no difference in the propensity of either fluid to retain entrained air. For all practical purposes, they were EXACTLY the same.

The compressibility differences between DOT-3 and DOT-5 fluid are de minimis. Fluids are "incompressible". The differences in "compressibilty" between them are not even worth talking about and I seriously doubt that they have any demonstrable effect on braking.

Keep in mind that the "DOT" in the rating refers to "Department of Transportation". The "-5" is the DOT standard to which the fluid complies. The DOT is responsible for setting standards for many safety-related automotive components. If silicone fluid had fundamental safety-related issues associated with it, then it would not comply with a DOT standard. Also, certainly no DOT standard would be set for a fluid which compromised safety.

Notwithstanding the above, DOT-5 fluid is NOT approved for use in most vehicles with "anti-lock" braking systems.

[Jim T.]

Re: Brake fluid

My 68 and 70 have had silicone brake fluid for over 15 years. The 68 has manual brakes and the 70 has power brakes. My 70's brakes have always impressed me with their stopping ability. With the silicone fluid I have not noticed any change, braking is excellent with the silicone and full hard pedal, just as good as it had with the original type brake fluid. Don't put silicone in a vehicle with anti-lock brakes.

[Terry M.]

Re: Brake fluid

I have had DOT 5 fluid in my 1970 Corvette since the early 1980s. No problems.
I put it in during a complete rebuild of the brake system. Flushed the lines with alcohol and shop air to blow them dry. Used the gravity bleed method to fill with DOT 5. The install was no problem either.
I left the original rubber brake lines in place, but maybe I was lucky. I don't recommend that to others. Do as I say, not as I do.

[Gary Bishop]

Re: Brake Fluid Update

I agree with Duke that it is best to start with a totally clean system. BUT when I changed my `62 over to DOT 5 I used the flush and fill method as I described in my articles published in the Restorer 95-96. About 2 weeks ago I bled and flushed my system to check for contaminates and such. The fluid was as clear as the new Dot 5. I still have a good pedal and have not had any problems.

[Duke W.]

Re: Brake Fluid Update

Over the years there have been a lot of reports of problems when switching to silicone from glycol using the "flush to fill" method. The two are not miscible and silicone based fluid has a much higher specific gravity. Most report considerable glycol fluid in the system when they finally pull it completely down for overhaul.

For this reason I only recommend changing over to silicone when the system is completely overhauled and you start with everything dry and squeaky clean.

Duke