brake light switich

[Ashley Page]

OK I will take the bait!
NEVER use Silcone brake fluid in anything?
Why?
We have been using silcone brake fluid since Mike Smith bought a pressure brake bleeder from the former Formula one Toleman team when they sold up.
If it is good for F1 why not a 356?
Does not attract water, has a higher boiling point, does not attack paint and so on.
PS Formula 1 are the guys that turn left and RIGHT if you didn't know!

ok, you took the bait - I'll grab the reel.
I would bet Toleman, as did many teams the world over in the 70’s, may have tried it. By the early 80’s (that’s 30 years ago!) it was pretty much history. It came and went faster than poop through a goose. It’s also a very safe bet they, like virtually every team that tried it, dropped it like a hot rock. The only places its used today is possibly some vintage racing (doubtful even there unless its in a truly vintage car that just parades around the track – even then it could be argued it’s a mistake) and maybe by a club racer who doesn’t know any better. The fact that it doesn’t attract water is not a good thing and there are fluids today with higher boiling points; not that that is an issue for any of us including the racers among us. Boiling brake fluid in a race car today is all but a thing of the past – if the car is put together correctly. But that’s all been covered very well here and everywhere over the last 30 years.
As for Toleman, just because they were around F1 doesn’t qualify for squat – maybe they did stick with it - they had more DNQ’s and DNF’s than finishes in their career. They never won a race. Maybe they never even scored a single point. They were kind of a laughing stock and an entry point for folks who went thru there (key word – thru) looking to get into a real F1 job. Not sure I would hang my hat on a decision they chose to follow.
Trying to make a case for silicone brake fluid is like trying to make a case for swing axle suspensions (all in good fun ).

[David Baugh]

John, one more thought concerning the melted plastic in the switches. If my conclusion is correct, and the residue is burned silicone .... as that residue builds up, the contact patch of the points would be reduced. The resulting constricted circuit should generate heat, particularly if it was "sputtering" before it failed.

Dave

[Norm Miller]

The after market switches are junk.
I took apart 2 failed switches and found that plastic had flashed over one of the contacts causing an open circuit.
I scraped the contact clean and tested the switch and it worked.
I replaced them with the last 2 german switches on earth and have no more problems.
The failures were with DOT3 fluid and as far as I can tell the fluid has nothing to do with failure.
The contacts are not exposed to the fluid.
I've driven Porsches and other cars for over 50 years using DOT3 with no problems so I fail to understand why so many are trying silicon.

Norm
Save the silicon for breast enhancement.

[Ben Wainscott]

Of the folks who have switched from DOT 5 back to DOT 3 or 4, was this done in conjunction with a complete brake system rebuild, or can you just flush the DOT 5 out of the system using DOT 3 or 4?

[Ashley Page]

Of the folks who have switched from DOT 5 back to DOT 3 or 4, was this done in conjunction with a complete brake system rebuild, or can you just flush the DOT 5 out of the system using DOT 3 or 4?

You may find some different opinions but I would want to rebuild the wheel cylinders or calipers and the master cylinder. Rebuild - as in if they are fairly new then disassemble, wash with soap and water and reassemble using the proper assembly grease (which oddly enough is silicone grease! Dow 111 being a good choice and compatable with any synthetic fluid). Best if you replace the rubber seals but if the old ones are not so old then reuse them. The lines can be flushed with brake clean aerosol. I don’t believe the two brake fluids are compatible.

[Bill Oldham]

Dot5 fluids do not mix with 3 or 4 so its a very bad idea to flush out one with the other. Plain old 96% isopropanol seems to be compatible with either fluid and its pretty harmless to us humans. So I always flush the lines out with isopropanol and blow out with air. Best to rebuild wheel and master cylinders, but I suppose they could also be flushed with isopropanol and blown out, never done that though. (Isopropanol seems to be pretty kind to rubber, at least for short exposures). And I use Dot 5 in all my cars that see very little use: the simple reason is that there is no corrosion of the steel parts. Even when the Dot 3/4 fluids are changed regularly, the air interface on the wheel pistons attracts water and corrodes. Look at any pistons when you rebuild... I have never had a problem but have only limited experience with 4 or 5 cars.
BTW good pressure switches are available if you do not mind an extra contact (VW bus switches have NC/NO contacts instead of just NO contacts. Just ignore the extra contact.)
bill

[Joseph Kuntze]

you folks got me paranoid so i went out and checked my brake lights (silicone fluid x 3 years)
all worked great

[Van Miller]

Group:
Thanks for all the imput. As per David Baugh, I am particulary sensitive to the inevitable lag time before you realize the brake lights are out. After reading all the posts I think it is time for me to change back to DOT 4. I should say that I have not had my single cylinder Master Cylinder system replaced in either of my two cars in several decades. Finally how much bleeding or how should I flush out the silicone to change back to conventional fluid?
Thanks,
Van Miller