Converting to Silicone Brake Fluid

[Brian K.]

Hi Guys,

Rebuilding all calipers and new non power master. 5-6 years ago, installed new stainless lines and rubber hoses. should I replace hoses again? What's the best way to flush the lines?

Did anybody not like the pedal feel after conversion?

Thank you for your input!

[Dennis O.]

Re: Converting to Silicone Brake Fluid

I converted my '68 about 15 years go. It was quite difficult to get bled. Since then it has worked fine, and I have been very satisfied with the results. When I did it, I didn't change any other components, which were still quite new. I just ran about 1/2 pint extra Dot 5 through when I bled each wheel. That being said, everything I have read over the last 10 years seems to indicate that Dot 5 is not worth the extra effort. When I did my '67 about 8 years ago I used Dot 4, and have been very satisfied with it as well. I guess it comes down to personal choice

[Jim L.]

Re: Converting to Silicone Brake Fluid

.....everything I have read over the last 10 years seems to indicate that Dot 5 is not worth the extra effort.

Huh? You may not have read anything I've ever posted on the subject.

The extra effort is mainly just bleeding the brakes at a glacial pace..... something which needs to be done exactly once. When compleat, you can pretty well forget about any part of your brake system corroding on the inside.

DOT 5 fluid is wonderful stuff and I'll never use anything else in my old cars.

Jim

[Domenic T.]

Re: Converting to Silicone Brake Fluid

Brian,

I flushed the system out with solvent then blew air thru the lines for about a hour on my 67.
I do not have power brakes and did not like the feel of the pedal whatsoever.
I think the power brake system makes it feel better because of the booster.
My pedal was high & hard with verry little movement, I was going to put a few bubbles in the line to get some pedal movement.
I did like dot 5 in a hhdraulic clutch on another car.

DOM

[Duke W.]

Re: Converting to Silicone Brake Fluid

The proper "solvent" for flushing DOT3/4 prior to using DOT 5 is denatured alcohol. Brake part elastomers are not compounded to resist attack from petroleum based solvents, and denatured alcohol is a better solvent for polyglycol ether brake fluids.

As long as you thoroughly flush and dry (relatively new) hoses and pipes, they are okay to reuse. Master and wheel cylinders should be thorough cleaned/dried as above and assembled with DOT 5. Any commercially bought new or rebuilt components must be disassembled, cleaned/dried as above, and reassembled with DOT 5 because they are always assembled with DOT 3 or 4. New brakes hoses should also be flushed/dried because the ends are swagged on using DOT 3 as a lubricant.

DOT 5 virtually eliminates the need to flush brake fluid periodically to purge absorbed moisture that can cause internal corrosion. Most unsuccessful installations are due to improper conversion procedures.

This subject has been discussed on the TDB countless times.

Duke

[Timothy B.]

Re: Converting to Silicone Brake Fluid

Brian,

When I did my 67 I cleaned all the old dot 3 out of the master cylinder then filled it with dot 5 and gravity bled all the brakes. I let it run until all was clear with the dot 5 and have never had a problem, although I did flush it good. I know it's not the text book way but I think sometimes you can create more problems than you fix. A very experienced Corvette mechanic told me to do it that way as he has done plenty, it's been 10 years now and no problems.

The brake pedal seems the same to me as before, I don't know why that would change.

[Brian K.]

Re: Converting to Silicone Brake Fluid

Master and wheel cylinders should be thorough cleaned/dried as above and assembled with DOT 5. Any commercially bought new or rebuilt components must be disassembled, cleaned/dried as above, and reassembled with DOT 5 because they are always assembled with DOT 3 or 4. New brakes hoses should also be flushed/dried because the ends are swagged on using DOT 3 as a lubricant.

Thanks Duke, I never considered that aspect.

[Jim T.]

Re: Converting to Silicone Brake Fluid

Just drove my 1968 again yesterday with manual brakes which was changed to silicone fluid over 23 years ago. My thoughts backing out of the garage and stopping, this brake pedal feels real good.

[Terry M.]

Re: Converting to Silicone Brake Fluid

I changed the 1970 to DOT5 about 30 years ago. I did it when installing stainless steel calipers. Rebuilt the master, although it didn't need it. Used DOT5 for assembly lube and flushed the lines & hoses with denatured alcohol. I followed the SAE books on the subject. They make for interesting reading.

I flushed once after about 25 years just because I thought I should.

Just pulled the car out of the garage after almost a decade of immobility. I stepped on the brakes and the pedal was just fine. I admit to being surprised at that outcome. I did use GM parts for assembly of the calipers and master. I am told the old GM seals are superior to today's product, but I have no basis to compare.

DOT5 FTW.

[Phil W.]

Re: Converting to Silicone Brake Fluid

I changed my '71 Power brakes over about 7 years ago. No more leaky calipers and the pedal feel is great - especially considering that before the change most of the time I didn't have much pedal at all...

[Domenic T.]

Re: Converting to Silicone Brake Fluid

I know this is not correct, BUT I was using my forklift and the brake pedal went to the floor. I only had dot 5 fluid and a job to finish Quickly.
I said I would flush the system when I fixed the reason the pedal went to the floor, that was a few years ago and all is still working great.
I am not saying that it is OK to mix but I had to do it and didn't have the pedal ever go down again.

DOM

[Jim T.]

Re: Converting to Silicone Brake Fluid

I changed the 1970 to DOT5 about 30 years ago. I did it when installing stainless steel calipers. Rebuilt the master, although it didn't need it. Used DOT5 for assembly lube and flushed the lines & hoses with denatured alcohol. I followed the SAE books on the subject. They make for interesting reading.

I flushed once after about 25 years just because I thought I should.

Just pulled the car out of the garage after almost a decade of immobility. I stepped on the brakes and the pedal was just fine. I admit to being surprised at that outcome. I did use GM parts for assembly of the calipers and master. I am told the old GM seals are superior to today's product, but I have no basis to compare.

DOT5 FTW.

Terry, Did you put any miles on your LT-1 after you pulled it out of storage?

[Terry M.]

Re: Converting to Silicone Brake Fluid

Terry, Did you put any miles on your LT-1 after you pulled it out of storage?

Not yet. The brake test was out of the garage (photos in a previous post) and onto a trailer. Just 3 or 4 brake applications.

I doubt the car will ever get a significant test of the brakes, or anything else, in the future. It will be a trailer queen for the rest of the time I have custody.

[John D.]

Re: Converting to Silicone Brake Fluid

SAE paper 810804 is a good reference on this topic if you can get it.

It says... "It was found that silicone brake fluids performed as well as or better than conventional fluid in all tests involving brake system elastomers...."
It goes on to say "brake performance of systems in which silicone and conventional brake fluid become mixed will operate normally with no fluid/elastomer based problems."

I would interpret that as meaning a few drops of conventional brake fluid left after a careful flushing of the system with silicone fluid isn't going to hurt anything on an old Corvette.
I have had it in my car for over 20 years with no problems at all

[Duke W.]

Re: Converting to Silicone Brake Fluid

Silicone and glycol-based fluids are not misible, and if you simply bleed a quart of silicone fluid through a system with conventional fluid there will be a lot of conventional fluid left. This may not cause short term problems, but the trouble is that this residual conventional brake fluid (a lot more than a few drops) is likely moisture contaminated and will cause internal corrosion that could eventually result in leaks.

Conventional brake fluid has a specific gravity of about 0.95. Silicone is much denser at 1.40, so the residual conventional will tend to migrate to high points in the system.

I've seen the results of several of these failed efforts, and it's not pretty. You can't go wrong by starting with everything squeaky clean (free of every last molecule of conventional fluid) and dry and assemble everything with DOT 5. Then if you properly bleed the system it will likely remain fully functional and leak free for decades without further attention, especially on a drum brake system. Disk brake calipers can pull in air or water splash depending on seal type and rotor runout.

It always amazes my how guys obsess over the accuracy of some small reproduction part, but many are far less rigorous when it comes to the brake system.

Duke