Silicone Brake Fluid?

[TheLoneRanger]

I have a 78 Bronco that's not driven very much, and is in need of another master cylinder. The MC's accumulate water in the cylinder bottom, and the resulting bore rust causes them to leak. I'm using DOT 3 brake fluid.

I'm considering putting silicone fluid back in it, when I change out the master cylinder. Is this a good idea, or not?

I've read the previous posts on DOT 3,4,and 5 brake fluid. Are DOT 5 and "silicone" the same?

Thanks for all opinions.
Don

 

[Ed]

DOT 5 is Silicone fluid but oddly enough DOT 5.1 is not. 5.1 is compatable with dot 3 and 4 and is a premium(expensive ) product.

Silicone fluids (dot5) have their place but aren't generally recommended for conventional brake systems. Just replacing the mastercylinder is not sufficient if your changing from conventional to silicone. The ENTIRE hydraulic system must be "As new" or your just wasting your money. If one is restoring a show car that will almost never be driven and in storage, it might be worth while.I understand that silicone fluid is slightly compressible and gives a funny feel to the brakes. Generally it's better to stick with conventional fluid and change it often. (every year or so)
Ed

 

[Ken2]

Also, silicone brake fluid allows the moisture to separate, so the water will pool and cause more rust. Standard polyglycol ether brake fluid absorbs the moisture and provides more (but not enough) corrosion protection.

Change the brake fluid more often. Where's that water coming from? Past the leaky master cylinder cap when the hood's open and water drains off?--just takes once.


Ken

 

[UncleS2]

Don,
For a little over 21 years, I owned an old Volvo 122S that had hydraulic clutch linkage, both slave & master cyl's were aluminum(Lucas-Girling)with steel plungers/pistons, & I had to replace the slave cyl at least 3 times, the master cyl at least once. For about the last 7 years I owned it, I used Castrol brake fluid in it & had virtually no problems with it after that. If I had your problem, I'd replace the MC, & fill & flush the whole system with Castrol brake fluid(LMA). If the MC's rusty, it might be worthwhile to replace the wheel cyl's too- & maybe even the calipers(disc front?) on a 25 yr old vehicle.

[ March 02, 2003, 09:18 PM: Message edited by: Stuart Hughes ]

 

[TheLoneRanger]

Thanks for the replies, guys. I guess the concensus is to stay away from the silicone, and change the DOT 3 more often. I was looking for a "fill and forget" solution, but it seems there's not one.

The Bronco has low miles (44K original), but I have had to replace a front caliper and two MC's because of rust. I don't have enough garage space, so it sits outside, and the weather is rough on it.

Stuart, I'll try some Castrol fluid if I can find it. Does the Castrol have some sort of additive in it that other brands do not?

 

[cryptokid]

the only thing i will say is a previous member is incorrect about replacing the entire brake system when converting to 5.

how do i know? i have done it myself on 1 car and 2 motorcycles.

you dont need to replace anything at all, just make sure the old fliud is out, and take proper steps to flush it.

with that said, dot 5 isnt worth it.

 

[Ed]

Really meant to say that the system should be as cleaned out as new not actually replaced

 

[cryptokid]

fair game my man

 

[Bror Jace]

When flushing out a brake system, what should you use? My brother did this to a bike (Suzuki GXE 1100) 10+ years ago and used some sort of alcohol. He coverted to Silicone DOT5 ... and then did it again months later (after hearing silicon horror stories) using up (my) DOT4 Castrol LMA.

--- Bror Jace

 

[UncleS2]

Special additives in Castrol fluid?

I really don't know, but it's the only brake fluid I can remember seeing that says it fulfills both DOT 3 and DOT 4 requirements. For years I didn't know what the LMA stood for, turns out it's Low Moisture Absorption. Sorry I can't give you a better answer.

 

[cryptokid]

you really shouldnt flush it this way, but the way i did it back in the day was to first drain the system of brake fluid. then disassembale the master cylinder, and calipers and clean them to bare matel inside (no more brake fluid) (i also did a caliper and m/c rebuild with kits i purchased at autozone at the same time)

while the calipers and master cylinder was off i flushed all the brake lines throughout the car with water. i then hooked up an air hose with a filter/dryer to blow out the water, and i let it blow for a real long time to make sure it all evaporated. finally i put the master cylinder and calipers back on and procedded to do the age old ritual of pump squirt pump squirt. it worked fine for me but these were older vehicles without abs and stuff.
dot3 and 4 brake fluid is water soluable (sic) so the water mixes with it and flushes it out.
the new dot5 felt a bit more spongy than good dot3-4.

the reason i dont use 5 anymore is the fact that if you flush your brakes every year or 2 you wont ever have a problem. its the OUTSIDE of the m/c and calipers the outer dirt/water seals that wear out, from heat and let contaminants in. so using dot5 is completely useless, it wont stop caliper sticking, only regular maintence of the outer durt/water seals will do that. if you have blown out outer seals, bleeding the brakes every 6 months wont stop caliper sticking.

the only viable use for dot5 is in a collector car that hardly ever sees the road.
also u notice i never said wheel cylinders, i dont own any cars or motorcycles that have drum brakes, id assume it would work but i dont have first hand expierence. heck i dont think i have ever even serviced drum brakes. my 71 porsche comes with 4 wheel discs from the factory
98 hondas dont even have rear discs

[ March 03, 2003, 10:26 AM: Message edited by: cryptokid ]