General Brake Question & repair manual

[Lotuswins]

Tahoe Healey,

Nope, not Dot 5, but Dot 4. Dot 5 is silicone, IIRC, but Dot 5.1 isn't....go figure. Anyways, the early british cars had natural rubber in the brake parts, mostly seals I would guess, and Dot 3 fluid would swell them up and sieze the pistons in the bores....this is all based on memory but there is alot of documentation on it. Dot 4 won't swell up these bits, so you had to be careful on which fluid you put into your british cars......

Thanks, Jerry

 

[Lotuswins]

Bob,

In the shop manual, section M.2, "IMPORTANT - Serious consequences may result from the use of incorrect fluids, and on no account should other than Castorol Girling Brake Fluid be used."

I'm not sure about the chemicals involved.....but I have always used LMA or Dot 4 racing fluids in my brit cars, and so far no problems (knock on dash....8^).

I believe all the repair or new parts Now provided do not include natural rubber. But if you don't know your brake system's history, its better to be safe.

Jerry

 

[Bob_Spidell]

I've gone about 80-90K miles in my BJ8 using silicone BF with no problems. I replaced all the seals before installing DoT 5. I've had both M/Cs out a couple times for other reasons and the wear patterns appeared normal. I did lose a foot valve on the M/C driving through Utah one time, but the damage to the seal appeared to be mechanical.

I put the silicone in many years ago on the recommendation of Norman Nock. Norman later rescinded the recommendation due to some issues with seals, but it's always worked fine for me. I put about 5-6K miles per year on my car. OTOH, we put Castrol LMA in our 100M after a complete system rebuild and it gelled after sitting a couple years.

 

[Lotuswins]

Hi Bob,

Fortunately, Silicone is pretty inert with respect to reacting to the elements of the brake system. I used it for many years on my 51 ford. The thing to watch out for is moisture sinks to the bottom of the system and isn't absorbed into the fluid, so you should still flush it out at 2 to 3 year intervals. Also, it becomes slightly compressable at elevated temperatures, which is why the race folks don't use it.

I also used it in my clutch on the ford, but that didn't go too well. I had premature failure of the rubber due to wear. Apparently Silicone is really a good lubricant for rubber on iron.

I'm surprised the LMA gelled in your 100M, were there other fluids in the system prior to the LMA? I'm wondering if they reacted in some way?

Jerry

 

[Bob_Spidell]

Hi Bob,

...
I'm surprised the LMA gelled in your 100M, were there other fluids in the system prior to the LMA? I'm wondering if they reacted in some way?

Jerry

Nope, it was a complete rebuild with a thorough cleaning, new rubber and mostly new components. The car sat in my folks' barn/shop for a few years with temperature cycles from near-freezing to 100degF or so--I suspect that may have had something to do with it (the fluid actually gelled and crystallized). We cleaned everything out and put Castrol back in, and so far no problems. We get the chassis/drivetrain out for some short runs periodically.

I've heard the military went to silicone BF because their vehicles experience similar conditions; i.e. sitting for long periods then being called into service. Now, I hear the military is moving to something besides silicone BF, but I don't know what the plan is. Because of this, silicone BF may become harder to get, so eventually I may have to use something else.

 

[tahoe healey]

They are supposedly going back to Dot 4 due to some oxygen absorption (not compressible) problems. May be the end of silicone as they were the main consumer.