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MG MGB Technical - V8 Brake Issue

I have rebuilt the brakes on my 1794 factory V8 but can‘t get a nice pedal.
I have rebuilt the front callipers, new rear wheel cylinders, new master cylinder, new brake lines with braded hoses and a new servo.
The brakes have been bled three times, by the up / down method and also by pressing the pedal down and releasing the bleed screw, I started furthest from the master cylinder first working to the closest.
The brakes work but there appears to be a lot of travel on the pedal, if I pump it,it does get harder but soon goes away. I have checked and there are no fluid leaks.
I have pumped the pedal with the engine off to expel all the air, started the engine with the pedal pressed down but don’t get the downward movement on the pedal I was expecting.

Please any suggestion welcome as I want to get the car in for MOT first one in 23 years for the car.
a goldup

Hello A.

If you pump brakes and get hard pedal staying hard until you release it and 20 seconds later you apply brakes and pedal goes down: you still have air in system

If pedal is hard and holding it; it goes slowly to the floor, it is a worn master cylinder most of the time...


Jean G.
Jean Guy Catford

The master cylinder is new.
The pedal stays hard all the time you have your foot pressed on it.

If I have air in the system how do get it out as I have bled the brakes three times with no sign of air the the bleed tube.
a goldup

Might not help, but in the past with various vehicles I often left it for a week or so after bleeding. It seems any residual air collects in areas and then is easier to bleed afresh. Mike
J.M. Doust

Also, try re-adjusting the rear brakes. You may have picked up some travel since the system was put together. RAY
rjm RAY

Is yours a Rubber bumper B? Chrome bumpers with remote servo have a couple of design faults. The servo piston is horizontal and the valve is orientated wrong. Lifting up the front of the piston helps as does twisting the servo so that the valve is at 4.30 as opposed to 1.30!! The factory vacuum bled the brakes so these faults didn't show at Abingdon. I have just bled my brakes. I modified the servo as mentioned, used a pressure bleeder AND pumped the pedal as well.
Allan Reeling

The car is a Chrome bumper with a remote servo,
Can you post a picture of the position of the servo on your car as I am not sure of what the position needs to be.
I get a good pedal on the second press of the pedal so I think there is still air in the system some where.
The car passed the MOT with all brakes at equal readings and the mot tester remarked on how well balanced the brakes where.Should be as the only two original parts left now are the pedal and the back plates.
a goldup

Have you read all the helpful stuff on Paul Hunt's web site?
Mike Howlett

Yes I email Paul on a regular basis. I have tried all the sugestions was looking for the golden bullet.
a goldup

After you deopress the pedal to expel air from the bleed tube make sure that you tighten the nipple again BEFORE you raise the pedal otherwise you will draw air in around the nipple threads and the system will always feel soft. This seems to be a point not often realised. So every time you depress the pedal you must tighten the nipple before releasing the pedal again opening it when the pedal is raised and before the next stroke.
Iain MacKintosh

I've just replaced both rear cylinders on a B, not a V8. Adjusting the rear shoes as described in the workshop manual will reduce the travel of the pedal. I was surprised how much effect this had reducing the pedal travel. This worked for me when I had similar issues.
Richard Thompson

When you rebuilt the calipers, are you sure you didn't get outer parts mixed up ? They will fit on either side but, the oil channels won't line up unless they are mated to their correct inner parts. Barrie E
B Egerton

Slack rear brakes will cause a long pedal, which may be able to be pumped up, but it shouldn't cause a soft pedal on the initial push, that is air.

You do have to press the pedal very hard in the second stage of caliper bleeding (the first being low-pressure as from an EeziBleed to refill the system) before opening the bleed nipple. Also the nipple must be closed again while the pedal is still down as stated. In practice the nipple is opened and closed in the same movement, which causes the pedal to go to the floor anyway.
PaulH Solihull

This thread was discussed between 12/04/2011 and 15/05/2011

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