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MG MGB Technical - Brake Pedal Mystery

Brake Pedal Mystery

I have a MG TD with MGB front disc brakes, a MGA rear axle with MGA drum brakes all operated by a MG TD master cylinder. My problem occurs after having driven the car the previous day, and then parking it overnight. For some reason, on the first application of the brakes, the brake pedal goes down about 3/4s of the way and the car pulls to the left, but does stop. On the second application, and all subsequent applications of the brakes, the pedal is hard and the car stops in a straight line. If, after driving the car 10 or 20 miles and then parking it for a few minutes, to go shopping for example, the problem does not occur.

These symptoms would indicate a leak in the hydraulic system. But there are no obvious leaks in any of the wheel cylinders or in the master. This symptom may also imply that the piston in one or more of the wheel cylinders is retracting and partially empting the cylinder
Frank Grimaldi

Brake Pedal Mystery - addendum

I don't know if this makes a difference but, the brake system uses silicone brake fluid.

Frank Grimaldi
Frank Grimaldi

Have you tried bleeding the brakes? I'd start there. It could be air in the system.
Ross Kelly

Frank the first stab 3/4 to the floor and back to normal on the second sounds like a master cylinder the pull to the left is a puzelment. Ric

You could also have a rotor that is out of round. This will push the pads further in on that side and it could lead to a pull. also if you have a sticky piston on that same side it too could create that problem.
With a TD master how are you operating the clutch?
On one conversion that I did I used an MGA master cyl.
conrad sanders


I had a truck that did the pull to the left thing. In fact, a light touch of the brakes would lock up the left front wheel for the first few applications (and pull the steering wheel out of your hands if you weren't ready for it). If I rode the brakes for a minute, all would be well till next time.

In my case it was a very slow leak at the left front wheel cylinder that would wet the shoes and make them grab till it was cooked off. I replaced it, cleaned everything up, and no problems since.

You might check to see how dry your discs and calipers are.

C R Huff

Frank - "and the car pulls to the left, but does stop" Check that the right front or rear is engaging properly. In fact the right front caliper is the one causing your problem both with the pull to the left and the low pedal as suggested above. Cheers - Dave
David DuBois

This thread was discussed between 29/06/2008 and 30/06/2008

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