View Full Version : TR6 TR-6 Brake Master Cylinder Seepage

08-23-2012, 02:14 PM
As it has been explained to me, the front surface of the TR-6 BMC casting, where it mates with the brake booster, has a small "V" shaped notch. I believe (haven't checked recently) the brake booster has a corresponding groove in the housing, such that both BMC and booster housing together create a channel, through which BMC fluid leakage can flow.

Point of this discussion is to request input as to what constitutes normal (i.e. no reason for concern) "normal" weepage from this channel, and at what degree of severity, would you consider BMC failure imminent ? I realize such assessments are rather qualitative at best !


Andrew Mace
08-23-2012, 03:00 PM
I'm not all that familiar with the M/C - booster setup on the TR6, but I don't consider ANY weepage (of brake fluid) as either normal or acceptable!

08-24-2012, 12:04 AM
Andy is right!

08-24-2012, 07:18 AM
I have a similar problem. Booster was rebuilt and master cyl was rebuilt by Apple. It all sat for several years while I did my restoration. I used the parts when I did the conversion on my TR4A to the TR6 dual setup. The master cyl leaks or weeps fluid but it's tough to know exactly where or how. I get some fluid on my hand when I run it under the booster but the amount that has leaked is more than I can see or feel on the bottom of the booster. Nothing inside the car on the back side of the booster and nothing in the vacuum hose either.
I do use silicone fluid and one friend told me that the silicone does not swell the seals as regular flid does. Apple has a disclaimer on their rebuild to not use Dot 5 fluid but i think that's as much a liability warning as anything else.


08-24-2012, 02:25 PM
Jerry, it is true that DOT 5 does not cause the seals to swell which may cause it to weep. You can take the nuts off that hold the master cylinder to the booster and withdraw the MC from the booster enough (you can do this without loosening or removing the brake pipes)to inspect the piston area to make sure its not leaking.
If everything on the inside is dry I would suspect that the leak is coming from the cap. I have had a similar situation and found that the caps just do not seal well. In my case I was still using DOT 3 fluid and got tired of the paint damage so then I switched to the silicone. I still have to really tighten the cap to get it to seal but at least now if it leaks it wont eat my paint.