hot running rear hub

[Gene Gillam]

Totally agree Stephan. If you like it, use it, if you don’t, don’t. I also have 20+ years experience with DOT 5 and have never had a problem.

[Steve Simmons]

My 67 MG BGT has been running silicone since 1980 and never an issue. I continued to run it because that's what the previous owner had in it. My MGA runs it because of the paint issue, which is clearingly obvious if you take a look at where the MC is located on those cars. Made the switch about 15 years ago. My 65B also runs it. The 69 mgc also runs it on a boosted system because the world's leading expert on performance and racing MGC's recommened it when the car was built 20 years ago. I ran it in my TC at one point also. No issues with any of those cars, ever. Nice stiff pedal, no corrosion issues and no moisture in the system ever. But as noted I live in a dry area, although I do drive in inclement weather when it happens and I tour to places where the weather isn't always so nice.

That said, I've never had an issue with glycol fluid either, on cars where it was properly maintained and periodically flushed. You can get away with going 20 years not flushing silicone fluid so long as no water gets in, but you have to flush glycol fluid now and then no matter where you live. At the moment, I run glycol And all the cars with the MC underneath, and silicone and everything with the MC up high. Just my choice of course.

[stephen stierman]

What we see in the cold damp winters of Ohio is if a car sits and now many of these cars sit for several years without use as owners get older and less attentive, the Dot 3 isn't touched and the hydraulics become a disaster. I restored my early Plus 8 Morgan in the early 90's and it goes years without being touched although it does get driven in good weather. The only time maintenance is required is when the brake light switches fail which seems to happen more frequently with Dot 5 and than the system gets a bleed and top up.

[Duncan M]

Steve- You completely did not understand what I said. Booster never fills with fluid. Booster never fills with fluid. It leaks out into the vacuum in a mist. Also, the common practice of keeping the M/C reservoir full to the line in a booster system should always be avoided, because most leaks start out very small. A small leak could go undetected.

Stephen, one could say the older vacuum booster systems would never start leaking if DOT 5 had gone in the system following a complete rebuild. Right? A good argument for silicone fluid keeping seals pristine. Either way, when/if the master starts leaking in a booster system like that, you never have to worry about unsightly drips on the firewall, or paint damage if using glycol, because the drips are being routed into the engine.

[Steve Simmons]

Depends on what kind of booster we're talking about, but if you mean a Girling booster then it can actually fill with fluid. A cutaway diagram shows the path where, following a seal failure, fluid can end up going a couple places it shouldn't. To get into the vacuum chamber where the actuating piston is, I believe two seals would have to be leaking. It would take a TON of fluid to fill it to the point that it would "pour" into the engine though. You're right though, the typical "leak" would likely be a misting through the air valve above the primary piston.

In any case, I've never experienced either kind of leak (lucky perhaps) but I only have two cars with Girling boosters and neither are daily drivers, so they don't get a lot of wear. I did see a major failure in a Lotus once though. Fluid was everywhere!

Interesting thought about silicon protecting the seals. But one thing I've noticed about silicone fluid is that it doesn't seem as slippery as 3/4, so I believe there would be just as much physical wear, even if the silicon was protecting the rubber from breaking down. My daily driver B runs silicone and I've had to rebuild the hydraulics just as often as the cars not on silicone. So there's a small bit of data I guess.

[stephen stierman]

Duncan, to be honest I don't have anything with a vacuum booster in the system on an old British car. My Plus 8 had one, but I chose not to install when I restored the car as they did not have a reputation for reliability in those days.

[Duncan M]

Stephen, none of the British cars I have owned had vacuum boost brakes, either. I especially like the TC for its chain operated clutch. The XKE saga is a dazzling case in favor of DOT 5, if someone has an open mind. Interestingly enough, the E-type people seem to have somehow taken the case of the boosted brakes as solid evidence against silicone. At least last time I checked 15 years ago. Curious thought process of people that have already made up their mind about something.

[stephen stierman]

Duncan, I really don't think that Dot 5 turns to sand, but if E type owners prefer not to use it, that is just fine with me.

[Duncan M]

That explains the sour grapes. Actually, I never said silicone fluid turns to sand.