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TR5/TR250 Is this even Theoretically Possible? [Brake Question]

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glemon

glemon

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So I went to take my car to an event on Su day night and I notice the brakes are making a weird whistling or sucking sound when I push the pedal. I check and the fluid is almost dry in the master for both the front and rear brake reservoirs.

Didn't have enough spare brake fluid to refill (Dot 5, flame away!) and no parts stores open so I refill Monday kind of check everythi ng out, no pools of fluid anywhere or obvious leaks.

Pedal feels good, high and firm, doesn't drop with sustained heavy pressure so I go for a short careful drive. I have filled it tonthe very lip of the separator between the two reservoirs in the MC (same set up as a TR6) so pretty easy to tell if any appreciable drop. No apparent fluid loss.

Check again today, still topped up, go for a couple more drives, stomp on the brakes where there is no traffic and I don't have to stop. All good. No sign of losing fluid.

Here is the kicker, I have a set of air filters with a vacuum hose to the pcv system, and a set of trumpets which I put on occassionaly and let the tube hang. Could there be some weird interaction with the PCV (stock round valve like used on TR and other similar era british cars) and the brake booster wherein it was sucking fluid out of the master cylinder when I didn't have the system all hooked up, or is that just crazy talk?

I did order a master cylinder rebuild kit (it isn't that old) and will probably tear into it and see what I can find out regardless.
 
When I had DOT5 fluid mysteriously disappearing from my TR6 clutch reservoir it turned out to be in the thick carpeted floor mat, and the padding under it. It seems the master was leaking and dripping down the pedal before dripping onto the mat. When I hosed the mat with water, the fluid was obvious.

It seems odd that the brake master would do the same thing, since it has two isolated reservoirs. It also seems unlikely to be vacuum related, since no fluid should be in the booster -unless the master is leaking into it.
 
Might depend on the car; but a typical vacuum brake booster is designed to withstand essentially hard vacuum (more than the engine can possibly generate). Likewise, the MC has to contain 1000 psi or more, so 15 psi of vacuum is nothing to it.

IMO you're going to find multiple failures, probably both MC and booster are bad and the booster has a bunch of fluid in it.

Might be a good idea to leave the vacuum line disconnected if you have to drive it before rebuilding or replacing them; as one of the supposed dangers of DOT 5 is what happens if it gets sucked into the engine and burned. But better yet don't drive it, as you may be on the verge of a sudden, total hydraulic failure. BTDT, burned the T shirt!
 
Randall, yes, you are probably right. The booster is original, kind of surprised it has lasted as long as it has, I will take things apart when I get a chance and see what I can figure out. I don't have much time to drive it or work on it now, major home projects starting including a new garage build.
 
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