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MG MGB Technical - Odd brake problem this morning

Driving to work this morning. Everything seem'ed to be ok driving down the road. Coming up to a set of lights, started to shift down, then all of a sudden no brakes. Was able to come to a stop, made a turn and decided to head back home. Tested the brakes again and they felt fine, so I continued a slow drive to work, sometimes if I pumped the peddle I would get some pressure, other times nothing. Finally arrived at work and popped the bonet up and checked to level of the brake fluid. The level of the fuel was fine, though somewhat muddy. Closed the bonet and decided to try the brakes again as they were soft when I parked. At this point this point everything feels ok, guess I will find out on my way home.. Hope its not the brake master?
GG Ginty

It sounds as if your master cylinder is bypassing on occasion. Pump it until you get pressure and then hold the pressure on the pedal, if it slowly sinks the master is bypassing.
John H

Took another look a few minutes ago. I drove the B around the campus and had no problems. The brakes seemed to be very tight. Could it be the actual brake fluid? When I checked the level when I parked my car this morning it was fine. I stuck my finger into the well and it there was a bit of sludge at the bottom. I wisked it around with my finger, put the cap back on, got into the car, put my foot on the brake peddle and it was nice and tight.
GG Ginty

The slugde may be the m/c seals dissolving.
Stan Best

Looks like your master cylinder is on the way out.
Iain MacKintosh

I can't imagine that it is anything other than the MC if you don't have brake fulid squirting out somewhere.

The fluid is bypassing the seal on the piston. As a matter of safety for you and others, sounds like time for a rebuild of the MC. Boy, is that fun!
John Lifsey

Time for a new M/C or a rebuild of the old one. I had a similar experience with an Audi we had many years ago. I hit the brakes one time and they dropped to the floor. Of course in a moment of panic, I released the brake pedal and hit it again quickly and hard and the car stood on its nose as all four wheels locked up. Everything worked fine for the rest of the day and I wondered if I had imagined the whole thing. A couple of days later the same thing happened again and I went directly to a parts store and got a M/C kit. When I took the cylinder apart, I found the main seal had a very small split in it where the skirt joined the flat part.

With all the sludge you see in the M/C, you need to do a complete system flush when you renew the M/C. Cheers - Dave
David DuBois

As has already been stated above, sound like you better consider doing something with your MC pretty soon!! However, not knowing what MC you have, or year of car, as John indicated, "Boy, is that fun"!! If you have a dual MC used from 1968 - 1974, and do not have a lot of patience and tools, FORGET IT!!! Just get another unit and get your car back on the road. If you can get it apart without scratching the chrome sleeve(required for sealing), otherwise you will be dripping fluid on your foot shortly thereafter. If you have planning on keeping the car, try and rebuild MC later as a back-up. Try(!!!!) to disassemble before ordering kit because, "Boy, it is not fun!!!!" If you have a 1975 - 1980 w/booster, I can’t imagine it being as bad as the previous dual MC but really have no experience with them.

HTH

Fred
Fred Wright

This thread was discussed on 27/06/2007

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