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Silicone Brake Fluid & Swelling Seals

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RobT

RobT

Jedi Warrior
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A bit of background -- About 2 years ago I compleatly rebuilt the break and clutch hydraulics on my TR250 and refilled them with Dot 5 Silicone fluid throughout, since Dot 5 is less likely to absorb moisture, and does not eat your paint if (when?) it leaks onto the paintwork. I have used silicone before without a problem.

I have been very happy with the brakes, no problem there. Perhaps a little softer under foot than mineral fluid but not a big deal.

In the clutch hydraulics however its a different story. I just swapped out my second master cylinder in less than 2 years. The failure mode of both was the same - the clutch tends to "stick", and when I pull the master cylinder apart, there is scoring where the metal piston the seals ride on have scraped the bore.

I called Apple Hydraulics before sending this one off for a rebuild (the first one to fail was a repo from TRF, the second my original rehoned & with an new kit also from TRF). The chap I spoke to thought the problem was the rubber seals swelling due to the silicone fluid. He said this was a common problem on British systems, and they will not warantee their rebuilds if you use silicone fluid.

Has anyone else on BCF heard this being a problem with silicone fluid, or had this experience? With clutch or breaking systems? Are there any rebuild kits that are more resiliant to silicone fluid than others?

Also Apple can resleave using brass or stainless. I was thinking of going with the stainless, as this is harder and less likely to score, as the previous two master cylinders have. Anyone got any thoughts on which way to go?

Thanks,

Rob.
 
Rob:

I have run Silicone for over 20 years in my BE without a problem. I am intending to continue using it in BE that I am currently restoring again.

Althought I have heard others having problems with it.

Patrick
 
Rob, a little off your topic, but related; my father rebuilt the hydraulics on what was then his AH Sprite, changing to silicone fluid about 20 years ago. No mechanical problems, but I had the master cylinder rebuilt a couple years back due to a leak (no scoring), and ever since the top seal (looks like cork) perpetually leaks. Requires a weekly top up, and of course the floor mat is now well lubricated. Is there a special seal material required when using silicone?

Andrew
 
Hello Rob,

I have used nothing but silicone brake fluid for over twenty years and in several different cars, quite a few rebuilds etc over those years and without any such problems.

My thoughts are that swollen seals will tend to cause the cylinder to stick but scoring requires something, such as contamination, to cause it. In other words, two different reasons. Contamination could be from topping up or that the cylinder was not thouroughly cleaned when re-built.

Alec
 
I have been using silicone for 13 years in both my TR6's and my TR3. No problems, until I purchased a repro. clutch master from a place in Kansas. The rubber didn't last a year. Rebuilt it with a TRF kit and have had no problems.
Had a nearly disasterous episode as a passenger in a friends' car when he lost his brakes. His rebuild kit also came from Kansas. He decided against silicone after his second rebuild and has had no further problems.
I will not buy rubber products from Kansas.
 
O.K. Thanks for the feedback on Silicone fluid - sounds like no one else is having a problem. So I think I will continue to stick with the silicone, and get the master cylinder resleeved in stainless steel - this is harder than the aluminium, and I hope will resist the scoring I have experienced with the stock setup.

Rob.
 
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