VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1937-1945 Silicon brake fluid

OK all you brake experts, since we're on the subject, I started using silicon brake fluid in my '41 several years back and have had no problems with it except that the brake light pressure switch seems to go bad on me every 2 years or so and I have to replace it. Could this be caused by the silicon? Has anyone had a similar problem?

Yes, the silicone brake fluid is the cause of premature brake switch failure. It has been known for about 20 years. I don't know if there is a switch for the old Chevys that will take silicone fluid, maybe someone has found one.

This is the first I had heard of this problem. Thanks for bringing it up. So, ChevyChip, when you change out the brake switch, do you get enough air in the system that you have to bleed the system out again? Or is it a simple, screw the old one out and screw the new one back in? I am rethinking whether or not to use silicone fluid, or just use the regular stuff. Advice?

Unless you see a real need to switch to silicone I would stay with the venerable Dot 3. Silicone has the higher boiling point but personally I never run a 38 at speeds or under conditions where the difference in boiling point, about 150 degrees dry or wet, will make that big a difference. Not to mention that Silicone based fluid, as apposed to glycol based, is slightly compressable. So you will have a slight spoongy feel no matter how well you bleed the breaks. Plus the prime reason that everyone wants to switch to Silcone, that is does not absorb water, is also one of the drawbacks to using it on older model brake systems. Most older model brake systems are not sealed with a flexable rubber seal at the mster cylinder well. So moisture can condense in the master cylinder and since it is not absorbed by the Silicone fluid will stay as a puddle of water somehere, rusting through your brake system. The Dot 5 fluids are, I believe, designed for racing/high performance use, not driving in the country on a warm Sunday afternoon.

Look at it this way, if you are rebuilding a 60 some odd year old brake system whether it failed or is just not up to snuff it is still 60 years old. If you rebuild it exactly the way it was originally, it will out last most of us.

Brian

I agree with Brian, I have been told by a former Wagner Brake employee the same thing about (DOT 5, silicone fluid)which was developed for sealed systems in military vehicles and aircraft. The only thing I can see that it may be better than (DOT 3) fluid is if the vehicle is stored for several years, it won't do as much damage as old used (DOT 3). (DOT 3) was designed specifically so that it keeps water that enters the system (in a vented system)from forming pockets of water because the DOT 3 allows the water to disolve in the brake fluid, the dissolved water in (DOT 3) is not a problem in the older vehicles since brake fluid was replaced in the system as normal brake maintenance was done, new shoes, new wheel cylinder kits. and evaporation. I don't see any advantage in useing it in a vehicle that is not stored several years between drivings, as long as you do the regular recommended brake maintenance.

I worked for the largest maker of brake fluid in the world and who also helped develop silicone brake fluid. The major advantage of silicone fluid is higher boiling point. With earlier disc brakes fluid boiling point was a problem. All brake systems will take in water through the rubber hoses, past the wheel cylinder seals and at the master cylinder. If glycol based system (Dot 3 or Dot 4) it is soluable in the fluid. There are inhibitors and other additives to counteract the water. When the fluid is heated (primarily by disk brakes) some of the water is driven out of the system. If too much water then steam is formed and the brakes can fail or fluid is lost. Doesn't happen too often these days. The additives are effective for 2-5 years in most modern systems. All major manufacturers recommend changing the fluid every 2-5 years. That way the acids and other corrosive materials plus the water is removed and the system will last indefinately. Therefore, every two - three years you should change the brake fluid by bleading each wheel cylinder. If the fluid in the master cylinder is cloudy or discolored it should be removed before starting the bleading and replaced by fresh fluid. Then blead until crystal clear fluid comes out each wheel. A hose on the bleader that extends below fluid level in a glass jar work best. It only takes a few minutes to do the job and helps give the spouse a part in maintaining the old Chevy. While you are at it drain the antifreeze/coolant and replace with fresh at the same time.

Hey! Chevy Chip, you said that so well, maybe I could get you to "learn" me how to play the bugle, reckon!
P.S.
You guys that are having brake switch problems may want to considering going to an arm type switch (like on the 51 & 52s)and maybe a '28 according to the 1927 and 1928 repair manual. I do maintenance on our VFD's 1967 K.J. 2.5 ton 6x6 and that is also a problen with it, it uses silicone fluid) :rolleyes:

[ December 31, 2001: Message edited by: MrMack ]

MrMack,
Thanks for the kudos. When I lurn a bit more then I can give you alitl edacatin. Bin prakticin but gets the dog to hollerin so sessions r few. Got me a nu trumpit. Shur makes som strang noeyes's Mayb we can do a duette in Rkansaw.

Chevy Chip, That sounds lack a deel 2 me, I will brang my old duck call, and we can make butiful music, in Arkensaw, but ifen' we ain't kereful we will be up to the fenders with razerbacks!

Hey, mack and Chip... your going to mess up the
registration for the Arkansas Tour and I need all the people we can get to keep my 27 / 25 running.
roy

Hey Guys, Just saw the topic about silicon fluid, and wanted put in my opinion. I have been using it in my 60 Impala for 10 years, no problems, there is one important advantage to it that was not mentioned, it does not hurt your paint!!!!! I had to open the system this spring before the Springfield trip, and it was just as clean as the day it was put in. DOT 3 looks like swamp water after two months. I have heard about the brake switch problem, this is not an issue fo my year car.
John

I want to thank all you guys for the excellent advice on my brake switch problem. To sum up, it looks like the fix is either to replace the pressure switch with a mechanical switch or change back to DOT3. You would think that some one would have developed a pressure switch that works with DOT5 by now. Maybe there's a business opportunity here!! :rolleyes:

ok all you brake repair people i,ve had si fluid in the 72 vett for 15 years no switch problem old push