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MG MGB Technical - Brake Master Cylinder Question

While driving my 74 B, I noticed that after stopping the car, the pedal would go down slightly after a few seconds. I assume that the seals in the MC must be going so am planning to rebuild it. I read that you can remove just the MC from the car, but am finding this to be quite difficult (especially the lower bolt that holds the #@$%#@$^ thing to the pedal box). Has anyone done it, or do I have to pull the whole pedal assembly?

Mike D

Mike, Someone mentioned in a thread a short time ago that he was able to get the master brake cylinder out without removing the pedal box. When I did mine a few years back I needed to remove the pedal box to clean, paint and get all the hardware back in the box cover so I removed the box and pedals. I don't recall the name of the thread I read the information in. Regards, Clifton
Clifton Gordon

Mike;
I use a flexable socket on the bolts. You can hold the bolt with a finger or 1/2 wrench stuck thru the round hole on the side of the pedal assy. You will have to push in the mc plunger with a long small screwdriver as you turn the mc anti clockwise to get it out. Is tricky but can be done. Now overhaul thats the real fun. Don't scare the chrome surface on the plunger. A new cyl is a smart investment unless it is of recent vintage say ten years or less. Bob Thompson/International Auto. Missed you clifton on our picnic and club meeting 73 de Bob
Bob Thompson

Thanks for the input guys. I was able to get it out last night without having to remove the pedal box. What are your suggestions for flushing out the system?
Mike D

Mike. Please re-read Bob T's comments. Pay special attention to the point about replacing the master cylinder rather than rebuilding it. This is in line with what other professionals have told me. I rebuilt my system (68GT) once, but it did not hold up well and was a bear to do. I replaced it with a new master cylinder a couple of years ago and have had no problems since. Somewhat expensive, but should last for the rest of my life. Change out the brake fluid every two years if using Castrol LMA, the preferred fluid. I remove the fluid from the master cylinder then use a Miti Vac to suck the fluid from the lines at each caliper or wheel cylinder. Then, refill the system and bleed. The cluch hydraulic system needs similar attention on a bi-annual basis. If you are really gung-ho, you can flush the system with alcohol (mentholated spirits). I have not found this necessary, but is required if you are switching from the LMA to Silicone brake fluid. Personally, I use the LMA because it is suitable for race use while silicone is not. Les
Les Bengtson

Mike

This sounds more like the servo to me (assuming you have a servo?). But - my experience of a 'normal' servo is that pumping the pedal with the engine off will produce a really hard high pedal. Turning the engine on then softens the pedal and lowers it as the diaphragm moves. That's not what you're getting so maybe it's irrelevant.
Dave
Dave Wellings

This thread was discussed between 28/08/2002 and 30/08/2002

MG MGB Technical index

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