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MG MGB Technical - Brake Problems

I have a 1971 mgb roadster. Last Friday afternoon, after leaving the MG 2006 show grounds, I am almost into Gatlinburg. The temperature is in the high 90's (F). Engine temperature is a little higher than normal but not overheating. Traffic is bumper-to-bumper. Most of the time I am idleing with my foot on the brake. The brakes started overheating and not releasing properly. Fortunately they never locked up completely and I managed to make it to the Friday night NAMGBR reception. After the reception and a mini cloudburst, I started home (I live nearby). In Pigeon Forge, I again hit bumper-to-bumper traffic and had the same problem. Once I cleared the Pigeon Forge Traffic, the brakes cooled down and I made it home OK. I had the same problem on Memorial Day with my 1970 E-type. The E-Type locked up completely and I had to trailer it home. I haven't had the cars back in heavy traffic but under light traffic conditions, both appear to be operating normally now. Since I live in the Gatlinburg area, both cars are routinely driven in heavy traffic conditions and I have never had a problem before. Does anyone have any idea what the problem can be and/or how to correct it?


A Sneed

If only one wheel was locking up and overheating then it is probably the brake hose that side, they split inside and a flap of rubber can act as a one-way valve.

If both wheels were aftected it is not unknown for the remote servo to lock up in hot conditions, my UK 73 roadster does it. The symptom is a much harder pedal or one with much less free play than normal. I don't know if the integral servo can also suffer from it. Fixes for this are said to be removing the little piston under the plastic disc and air filter on the servo and putting silicone grease on it, or turning the servo over so the air filter is at the bottom instead of the top.

Other possible causes of both wheels being affected are maladjustment of the (pedal box mounted) brake light switch, if screwed in too far it stops the brake MC piston from coming back all the way to fully clear the bypass port into the reservoir. When this happens if the fluid expands it cannot 'overflow' into the reservoir, but applies the brakes instead.

A 3rd possibility is a blocked or non-existant breather hole in the reservoir filler cap, again heat causes expansion but because the air can't escape it pressurises the fluid and so applies the brakes.
Paul Hunt 2

This thread was discussed on 27/06/2006

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