Brake Fluid Question

[Duane D.]

Over 20 years ago I replaced the calipers and master cylinder in my 1970 Vette with SS sleeved parts and silicone Dot 5 brake fluid. I have had to replace one caliper and put in new Dot 5 fluid during that time. My brakes continue to work perfectly.
Recently, to save NCRS deductions, I have had my original master cylinder rebuilt and planned to replace the SS master cylinder and continue to use the Dot 5 fluid. However, when the rebuilt cylinder arrived, the company that did the rebuild had a footnote that said they do not recommend Dot 5 and want me to use Dot 3 to maintain the lifetime warranty. The rebuilt cylinder has a brass sleeve and not SS.
Question: Do I continue to use Dot 5 and risk premature failure of the master cylinder voiding the warranty?
Or: Switch to Dot 3 wondering what happens to the caliper seals that have lived many years in a Dot 5 environment?
I have read the many threads in the NCRS archives on brake fluid and still don't know what to do.

[Joe L.]

Re: Brake Fluid Question

Over 20 years ago I replaced the calipers and master cylinder in my 1970 Vette with SS sleeved parts and silicone Dot 5 brake fluid. I have had to replace one caliper and put in new Dot 5 fluid during that time. My brakes continue to work perfectly.
Recently, to save NCRS deductions, I have had my original master cylinder rebuilt and planned to replace the SS master cylinder and continue to use the Dot 5 fluid. However, when the rebuilt cylinder arrived, the company that did the rebuild had a footnote that said they do not recommend Dot 5 and want me to use Dot 3 to maintain the lifetime warranty. The rebuilt cylinder has a brass sleeve and not SS.
Question: Do I continue to use Dot 5 and risk premature failure of the master cylinder voiding the warranty?
Or: Switch to Dot 3 wondering what happens to the caliper seals that have lived many years in a Dot 5 environment?
I have read the many threads in the NCRS archives on brake fluid and still don't know what to do.

Duane-----

There is absolutely no problem, whatsoever, with the use of DOT-5 silicone fluid with a brass or stainless steel sleeved master cylinder. I think the concern implied by the "warning card" that came with the master cylinder has more to do with the seals used in the rebuild than the master cylinder, itself. Some folks think that the standard seals designed for use with glycol-based brake fluids (i.e. DOT 3 and 4) will not hold up to DOT 5. However, you know otherwise since your original master cylinder used such seals and it gave outstanding service with DOT-5.

Another point: I think you'll find that the "lifetime" warranty of the master cylinder applies ONLY to the sleeving and not to the rest of the assembly. So, you don't really have a lifetime warranty on the complete master cylinder assembly, anyway. If the master cylinder sleeving ever does fail (which is highly unlikely and why rebuilders are wont to provide such a warranty on the sleeving) it WILL NOT BE due to the use of DOT-5 silicone fluid.

I would use the DOT-5 fluid with the rebuilt master cylinder.

[Duane D.]

Re: Brake Fluid Question

Joe,

Thanks for your reply. Your comments are most appreciated and I plan to use Dot 5 with the rebuilt cylinder. Damn the torpedos, full speed ahead.

Duane

[Jim T.]

Re: Brake Fluid Question

Duane just this year I installed a master cylinder rebuild kit in my 70's master cylinder because it was leaking DOT 5 out of the rear. Have used DOT 5 fluid for more than 20 years.
When I removed the master cylinder for rebuild I protected the disconnected brake lines with rubber caps to keep them clean.
I performed a through bench bleed of the master cylinder and installed it. I loosely connected the brake lines and let the new DOT5 gravity drip from both connections and then tightened them.
I did not do anything else. Had great pedal and the driving test of the brakes was very good. This was months ago now, and no problems.
I had done this same procedure on my 68 years ago and also had good results.

[Duke W.]

Re: Brake Fluid Question

Keep in mind that the new M/C was assembled with DOT 3 fluid. You need to disassemble it, clean everything in alcohol, and reassemble it with DOT 5 fluid.

If you never changed the original DOT 5 fluid from twenty years ago, now is a good time to flush the system with fresh DOT 5.

Duke

[Peter J.]

Re: Brake Fluid Question

Duane,
I've had Dot-5 in my 66 for over ten years and no problems.
Pete

[Jim L.]

Re: Brake Fluid Question

Joe,

Thanks for your reply. Your comments are most appreciated and I plan to use Dot 5 with the rebuilt cylinder. Damn the torpedos, full speed ahead.

Duane

Duane, just to reinforce your decision..... I use DOT 5 in all of our collector cars, even the two that see track duty. Never a problem. I wasn't even all that careful when converting one of the two track cars to DOT 5 (i.e. I didn't flush out the residual DOT 3 fluid first). Nooooooo problems, ever.

Full speed ahead!

Jim

[Steven B.]

Re: Brake Fluid Question

Duane, in '83 I installed SS sleeved calipers in my '77 and put in Dot 5. Never a problem.

[Paul C.]

Re: Brake Fluid Question

I had my 71 MC rebuilt and switched to Dot 5--no problems. Brakes feel as good as with Dot 3.

Paul

[Michael G.]

Re: Brake Fluid Question

Are any of you using the o-ring seal rather than the older style lip seal in your calipers?

[Dale S.]

Re: Brake Fluid Question

I dont know how I got so lucky. My lifetime SS calipers( big name company) has started to leak twice (same one) using dot 5 in the last 10 years. Rather than send it back we just rebuilt it. Now on the second time leaking, I think that one needs to go back. We thought it was the rubber seal. What is the o rings I was reading about here on the board? Are the piston grooves different for the o rings? I remember the old Wagner caliper overhaul kits with the type 1 and type 2 pistons. Thank you Dale

[Joe L.]

Re: Brake Fluid Question

I dont know how I got so lucky. My lifetime SS calipers( big name company) has started to leak twice (same one) using dot 5 in the last 10 years. Rather than send it back we just rebuilt it. Now on the second time leaking, I think that one needs to go back. We thought it was the rubber seal. What is the o rings I was reading about here on the board? Are the piston grooves different for the o rings? I remember the old Wagner caliper overhaul kits with the type 1 and type 2 pistons. Thank you Dale

Dale-----


I strongly suspect that your problem relates to a defective caliper sleeving and has nothing to do with the type of fluid. The problem may be extremely subtle, though, and may simply involve an off-spec bore finish that causes premature failure of the seal. As a matter of fact, if you have three calipers that have sealed well for 10 years and one that's needed to be rebuilt twice in that time, you can just about bet the problem is with the caliper and not the fluid.

O-ring type seals for 65-82 Corvette calipers have become popular in the last 20 years, or so. This style conversion requires special pistons and o-ring seals. Everything else is pretty much the same. Some of these do eliminate the piston springs while I believe others use the springs, though.

The o-ring pistons and seals seem to work quite well, particularly for cars which see a lot of "sitting time" and not subjected to racing uses. The o-ring design also eliminates the problem of "air pumping" due to excessive runout on the rotors.

[Timothy B.]

Re: Brake Fluid Question

On my 67 I sucked out the old DOT3 fluid from the M/C and installed DOT 5. I did this after having to overhaul the seals in the four SS sleeved calipers because of leaks. The only flushing was with bleeding and I did that very well. Never had a problem bleeding and no leaks, pedal great all the time.

On my 63, the DOT 5 was installed from the complete brake overhaul and the car sat for 20 yrs, the pedal is the same now as before (great) but I did flush about five years ago to put some new fluid in the system.

[Brian M.]

Re: Brake Fluid Question

I've been using DOT 3/4 for 35+ years with NO problems.

[Duane D.]

Re: Brake Fluid Question

Thank you all for your help. I feel very confident in using Dot 5 and plan to flush the system with new Dot 5. I am sure my one SS caliper failure was not a seal failure, but a caliper body failure. Currently, all four calipers are working perfectly (three are 22 years old and one is two years old) on Dot 5.