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MG MGB Technical - Brake bleeding Problem not in archives

I have a 69B but this is question for a mate of mine who has a Sunbeam Rapier. I hope there is no problem with posting this question here. The brake master cylinder was overhauled about two years ago. Two weeks ago he replaced the rear axle seals and brake shoes etc in preparation for an early morning run with a group of us comprising mostly B’s but with some other exotica thrown in for good measure. After bleeding the rear brakes (and flushing through at least 250ml of fluid) using a clear tube in jar of brake fluid there was no brake pedal resistance at all. Not even after the pedal is pumped. (At this point the front brakes have not been bleed at all.) The brake shoes appear to be properly adjusted. Could there be enough air in the lines to the front wheels to cause this? As mentioned earlier the master cylinder has been overhauled with stainless steel liners so we doubt this is the problem and there is no fluid leaking at all inside the firewall. There are no other leaks in the system at all. Is anyone able to shed any light on the problem please? Many thanks.

PS if you’d like to visit an Australian web site with some photos of some lovely cars visit http://home.vicnet.net.au/~escapees/IntroPage.htm Mine is the red roadster next to the magnificent MKII Jag on the June run.
G A Crutchley

Your question is a little confusing.
Has the car been used since the master cylinder overhaul two years ago?
When the rear shoes were replaced were the slave cylinder pistons removed or disturbed in any way?
Have you tried bleeding the front brakes?

Mick
M F Anderson

If there's no resistance at all, and no leaks, then it sounds to me as though the master cylinder seal has either gone bad or flipped over at the rim so that it no longer seals.
Miles Banister

Mick, thanks for your comments. The car has been used since the master cylinder was overhauled. When the rear shoes were replace the slave cylinders were removed and re-installed without any unnecessary disturbance. The fron brakes haven't been bleed yet - there didn'y seem any point as there is absolutley no resistance to the pedal.

Mike, if the master cylinder seal has either gone bad or flipped over at the rim so that it no longer seals would there be brake fluid leaking at the firewall inside the car?

Thanks Gary
Gary Crutchley

Gary, I suspect the Rapier does not have a dual master cylinder as used on USA cars beginning in 1968. If it does not all four cylinders need bleeding to get brakes. Good luck. Clifton
Clifton Gordon

Gary,

You need to solve these problems in a methodical way. If you just go from one item to another at random you will only complicate it.
Were the brakes working OK before you removed the rear shoes and rear cylinders?
If they were, do not start looking at the master cylinder, but go back over your earlier work.
You say that you have "absolutely" no pressure, and yet the rear brakes have been bled. How do you know the rear brakes are bled? Did you just see some fluid come out?
Did it just run out or come out under some pressure?
I am not sure with Sunbeam Rapiers, but with many English cars you can install clutch and brake slave cylinders upside down.
First check is that the bleeder valve is at the top of the slave cylinder.
Do you have a pedal lever return spring fitted (very difficult to bleed a slave cylinder without one)?

Mick
M F Anderson

Gary, If it's like the master cylinder on my B then it contains two seals. One develops the pressure and the other keeps everything tight behind it. What I was thinking that maybe the pressure seal has flipped leaving the other in place. Miles.
Miles Banister

Gary, Just had a thought - does it have a hydraulic brake light switch like our Bs ? If so then unscrew the switch and press the pedal (with a rag in place of course). If fluid comes out under pressure then the master cylinder must be good. If it hasn't got that kind of switch try loosening the pipe from the master cylinder at the first junction and test there. Miles.
Miles Banister

Thanks for all your comments. We now have something to go on.
Gary Crutchley

This thread was discussed between 09/06/2003 and 10/06/2003

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