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MG MGB GT V8 Factory Originals Technical - Silicone update
|I just checked the spare set of seals for my hydraulic throwout bearing again. Some may recall that I immersed these seals in dot5 silicone brake fluid some time back to test compatibility. It's been 4-1/2 months since I began the test and I am pleased to report that the seals show no signs of deterioration whatsoever. No size change, no softening, no reason to think that there has been any change at all. Can't see why I shouldn't use the silicone fluid.|
What are the seals made out of? Neoprene? Live (Natural) Rubber?
|Good question. Nytrile maybe, or possibly butatdene. Good stuff I think.|
The problem with silicone,
(1) It lacks the proper lubrication properties. You will find that the cylinder does not release smoothly.
(2) With altitude changes, the silicone fluid has problems with air bubbles forming resulting in a mushy pedal. Kind of like a diver getting the bends.
Both of these can be a real problem in a brake system. For a release bearing, it may not be a much of a factor.
IMO ,Stick with the DOT 4 and change it every year. That alone will give you max life out of your components.
Altitude problems are a new downside to this fluid, could cause a few problems descending the alps and those hairpins.
IMO only possible use for this fluid is in museum pieces when brakes are not required.
There's been a long running controversy on this BBS about silicone fluid. Despite such dubious attributes as causing some seal materials to degrade and fail, poor lubrication causing pistons to hang up in their bores, air retention, and making the system a bear to bleed, the advocates of silicone fluid mistakenly point to the fact that it does not "absorb" moisture. This is true. It is also true that moisture (water) does nevertheless get into the system from the atmosphere. Water, being heavier than silicone fluid, then accumulates in the low points of the system and forms puddles. When sub-freezing temperatures strike, the water then forms ice, sometimes occluding the system. As if this isn't bad enough, it is incompatible with any other brake fluid and I've never heard of anything that will flush it out completely. Once you change over to it, you're committed to it unless you disassemble and rebuild the system. Perhaps the only real saving virtue of silicone fluid is its ability to resist heat. However, there is a synthetic brake fluid that for all practical purposes matches it in this area of performance without sacrificing the vitues of more orthodox petroleum-based fluids: Valvolene Synpower. Being heavier than water, any moisture stays at the highest point in the system, i.e., the master cylinder where it can be easily removed with a turkey baster syringe. It's compatible with all types of seal materials, lubricates better than ordinary fluid, can be flushed out with alcohol, and with a dry boiling point of 513 degrees F (Hot enough for you? The wet boiling point for DOT 3 is a miserable 284 degrees F), why should anyone want to use silicone fluid when there's something that's so obviously better?
I have been using silicone fluid for years with no problems. For me I like the fact that if my master clyinder ever leaks, I can just replace it, and not have to repaint the fire wall at the same time!
|Well Steve, that's the most well thought out statement on the comarison of brake fluids that I think I've seen yet. Well done. Might even make a convert!|
I've used silicone fluid for, oh, about 20 years now. Although I haven't had any problem at all with water collecting or freezing (maybe the heat evaporates it) I do like the idea of a heavier than water fluid if it doesn't absorb water.
I've also not experienced the air bubbles. although I've driven from coast to coast over mountain ranges and everything in between, in all sorts of weather.
Kelly, though I appreciate the tip about sticking parts, I suspect that is not so common either. Maybe dot 3 or 4 is a better lubricant, maybe not. Sure doesn't feel any better between the fingers, but maybe it's just the nature of the stuff. Anyway I've not had anything stick with the silicone, so I suspect it's lubricating properties are acceptable.
And Bill, I agree. I don't like seeing bare metal just because a seal got tired and gave up. Has to be a better way.
Now one problem I have had is with whatever oddball blend NAPA sells as silicone fluid. Although it seems to work OK, it goes bad in about a year, and turns brown and nasty.
So does this Syn-whatever eat paint?
I saw your car at Minn. It is gorgeous! I can,t remember if you what type of clutch release you have. I am about ready to recharge my brake system (just fired up the 8 for the first time last nite) and have a Mcleod hydraulic release bearing--it specifically says in the instructions not to use silicone fluid. Bill, do you have a hyd. rel. bearing--any problems with it and silicone.
Yes, I not only pontificate, I proselytize as well. I'd like to see this stuff used in everybody's car.
To answer your question about Valvolene Synpower's potential for paint damage: I accidently knocked over and spilled about a cup and a half of the Valvolene Synpower fluid while putting it in (Clumsy, Stupid Me!) and immediately went into a state of near-panic as I envisioned the nice and shiny Mineral Blue paint of my tidy over-restored engine compartment bubbling before my eyes! I prayerfully cleaned it out (Oh God, No. Please No. No, No, No!) with ordinary blue Wesley's car wash fuild and plain water, then dried it with a bath towel and examined the exposed areas carefully. No damage at all! In all fairness I should point out that the instructions on the can state "Will damage car finishes", but it seemingly isn't near as destuctive as the DOT formulas. On the principle of safety alone, if a hydraulic system is found to be leaking, it should be repaired immediately. If the paint bubbles up, then the owner must accept his own responsibility for ignoring and/or neglecting the routine maintenance of checking the system whenever the car is washed (usually weekly).
Now I have a question for you: since you change your silicone fluid yearly, do you know of anything that can be used to flush and purge the system? Alcohol will dissolve Synpower, DOT3, and DOT 4, but I know of nothing that will do this with silicone fluid.
|On flushing the silicone fluid, First let me say that I quit using the NAPA stuff once I found out how it acts. Other higher quality silicone fluids don't seem to have that problem. |
Therer's no way I know of to completely purge the fluid except to disassemble the slave cyl's and clean them out, and pretty much the same for the masters. However, when replacing that NAPA stuff, I just put in the new and pumped out the old. Not complete I suppose, but it doesn't seem to have caused any problems.
I am using shortened GM throw out fork with a Toyota Landcruiser slave (13/16" bore).I was using a 3/4 bore slave, but when I changed to the 10.5" clutch, the clutch feel wasn't quite right. The 13/16" slave seems ideal for my set up.
No problems with silicone fluid, but I have never tried using a hyd. throw out bearing.
Thanks for the response--for now I will stick with the conventional fluid.
This thread was discussed between 01/08/2001 and 09/08/2001
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