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MG Car Repair/54MGTF brake problem

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Question
I have vacuum bled and bled with a friend pumping pedal and have a solid pedal. The car sits for an hour and the first push the pedal goes to the floor.The second push gives a normal pedal. Does the master cylinder have a valve to retain a residual pressure?
If so do I need to replace the master cylinder?

Thanks for your time

Answer
Hi Jack,

From what you tell me I would not think that you have any hydraulic problem. It sounds more like you have movement or travel problem.

Do this, pump up a good peddle and hold it while you pull and set the hand brake on hard. Then let it set for the time that you usually note the loss of peddle. If you have a good peddle after the time waited, then you problem is in the rear brakes. If you still have lost peddle then the problem is in the front brakes.

Hydraulic problems will cause soft peddle and since you have a normal peddle after one pump is a clear indication a wheel cylinder is moving so far that it requires two strokes of the brake peddle to seat it again. This is usually caused by incorrect brake adjustment procedure.

Another method to prove it is a travel problem is to adjust every brake adjuster so as to keep every brake locked up solid. Then pump up the brake peddle and it should be rock hard. Then let it set for the hour and check it and if it is still locked up. adjust each adjuster so they just barely free the wheel up but still make a slight dragging sound as you hand rotate the wheel. It may be necessary to adjust only one wheel and then let it sit for an hour and check it after the adjustment of one wheel at a time to pin point which wheel is causing the problem.  A shoe that does not hit squarely and is cocked to one side can cause this. Doing one wheel at a time is the only way to ID the wheel causing the problem as you can't see inside when it is working.

Let me know,

Howard  

MG Car Repair

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Howard M. Fitzcharles III

Expertise

MG from 1956 (USA versions only) up and Engine theory.

Experience

Dealership line mechanic on MG, Triumph, Jaguar for 15 years, Instructor in commercial mechanics school 2 yr. Product information manager for piston and valve manufacture, Instructor & hotline answer man for import car parts importer 15 yrs.

Organizations
Associate member SAE EAA member

Publications
Import Car magazine

Education/Credentials
ASE Master Auto with L-1 certification up to 2000

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