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MG MGB Technical - Spongey Brakes

Last weekend I made the fatal mistake of stopping to look at a 73 B for sale on the side of the road. Unfortunately for me the engine turned right over and sounded as only a British roadster can sound. Anyway I drove it home. It is a joy to drive, but the brakes are behaving badly. When first applied the brakes are great but after several seconds the pedal slowly gives way, pumping regains stopping power. The low pressure light has only gone on once. The brakes, pads and shoes look good, the previous owner claims less than 2000 miles on them. I can find no leaks. This leads me to think the problem is in the master cylander, or portioning valve? Before I tear into though I thought I would seek out the collective wisdom of the bulliten board. At some point I'll do atotal overhaul, but I would like to enjoy a little more fall driving.
Marty Zidron

Hi,

Good move buying the "B". It would seem to me that the master cylinder seals are starting to fail. If I were the new owner, I would certainly refurbish any brake parts that look dubious. Its your safety as well as others on the road that is at risk. These parts are not very expensive and very easy to replace. A couple of hours work to replace the master cylinder, brake hoses and bleed the system. I just recently bought a vehicle where the previous owner had replaced the idler arms on the front suspension and had one backwards... At least after "doing the brakes" you will know where you stand, and have more confidence driving the car. FWIW Alan
Alan

I'm in complete agreement with Alan.

When I bought my wife's roadster I few years ago, it had been in storage for a couple years, but the brakes in that time were "more than a little spongy" - they barely worked. They need a complete flushing and replacement of fluid, new wheel cylinders, and a master cylinder rebuild. As my wife was going to drive the car- and these were the brakes, I had no interest in incremental approaches.

If the car had been in storage, even if only for a couple of years, the seals could have dried. Since the brakes were refurbished in 1996, they've been fine. (touch or knock wood)
John Z

Marty,
Agree with the master cylinder as the culprit. Don't wait too long - if you already have to pump to regain braking, it probably won't be long before that will not work.

Pat
Patrick Callan

Leaking rear wheel cylinders can give similar
symptoms to a bad MC. They are cheap to replace
(check the archives for suggestions about the
infamous e-clips.)
Ronald

However leaking cylinders or calipers cause fluid loss, leaking seals in the MC don't.
Paul Hunt

Paul, what I found was that rear
cylinders can leak very slightly (noticeable by boots moistened with brake fluid) without causing
a visible drop in brake fluid level.
However, even a slight
leak in the rear cylinder(s) causes a lot of
air to enter the system, hence mimicking an
internal leak in the MC and spongey pedal.

Ronald

This thread was discussed between 21/11/2002 and 24/11/2002

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