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MG TD TF 1500 - TF MC Leaks Brake Fluid

Gentlemen,
Got the TF out of storage and the drive home suggested that it was time to pull the wheel drums and attend to the brakes. I have completely disassembled all wheel cylinders, cleaned them up, and reassembled them to the car, including the brake shoes, and all. I have yet to bleed the system. So today when I attempt to do just that, imagine my surprise to see brake fluid dribble out of the breathing hole on the filling cap of the master cylinder. I know that the system will have quite a bit of air in it since all wheel cylinders were removed from their flex hoses, etc., and at present all bleeding screws are securely tightened. So, just exactly what is going on? Do I have too much brake fluid in the MC?
Gene
Gene Burgess

Gene, The fluid should be just below the threaded lip going down inside the cylinder. When you bleed with the lid off, it will sometimes squirt up and inch or so, so if it is overfilled could come out the cap vent. Or the MC seal could be bad and the pressure is leaking back into the reservoir. George
George Butz

George,
Thanks for your input. I've had a rethink of the problem and I'm convinced that this problem has nothing to do with the master cylinder being bad, and everything to do with the fact that I've drained a large portion of the fluid in the system when I removed and cleaned up all of the wheel cylinders. I haven't bled the system yet (waiting for some help to do the two person pump the pedal and open a bleed screw routine) and a large portion of it is full of air. And with the brake pedal moving through its full arc from rest to the floorboards, the master cylinder piston is traveling its full stroke of several inches, rather than say one half inch under its normal circumstances. I figure that the large amount of brake fluid trapped behind the piston during its full stroke fires it straight up at the filler cap. I haven't tried it yet, but I'm hoping that when I get to bleeding the system, that if I push the brake pedal down slowly, the leaking through the cap should not occur. Does anyone agree with my thinking here?
Gene
Gene Burgess

Gene,
You are correct in your thinking. I always pre-bleed on the bench before fitting M/C's.Only yesterday I got a face full of fluid after fogetting to replace the cap, fortunately I wear glasses which protected my eyes. By the way the pre bleed proves the M/C is OK as we have had a couple of repair kits with oversize seals which cause a slow return or even brake lock on in one case.
Ray
TF2884
Ray Lee

Ray,
Thanks so much for getting back to me. I knew that the MC was fine when I put the car into storage last fall, and I had brakes when I brought it out last week. There was no evidence of any leaks anywhere in the system, but the day I pumped the brake pedal and saw the fluid on the floor almost caused a stroke. Thanks again!
Gene
Gene Burgess

This thread was discussed between 23/04/2008 and 26/04/2008

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