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MG MGB Technical - Brake Booster clunk

Sorry in advance for the long post.

After a rather scary episode on the freeway where my '68 B decided to slide all over the road under braking, I decided that it was time for a full brake rebuilt.

The master cylinder can was rusted, so I got a new one with the plastic can, I installed a Brake booster kit from Moss, new brake lines and new rear slave cylinders.
I rebuilt the front calipers.

The brakes bled reasonably, with some residual sponginess. I then had the local brake place check the operation and the bleeding - they managed somewhat better.

Now the brakes operate very well, nice and hard, no fade or pull - except...

When I apply the brakes, there is a decided 'clunk' felt through the pedal. I investigated and found the clunk (probably a slight exaggeration - but it's the closest description I have) was coming from the brake booster.

Finally ! - my question - is it supposed to do this? or do I have a problem booster? It was installed following the instructions, with the breather pointing slightly down.

Thanks in advance for your help
G Ward

No it shouldn't clunk. Are you sure the noise is coming from the booster? Often that sort of noise comes from the disc pads moving slightly, or even the caliper bolts being loose. If you have wire wheels it could be play in the hub splines.
Mike Howlett

I know you have the booster, however I dont and with greenstuff or OE pads my car stops fine with surprisingly low pedal pressures and amazing brake feel. Justto say to others, you may not need the booster, if it isnt fitted it cant go wrong.
Stan Best

The clunk is definitely coming from the booster.

G Ward

Which end of the booster is pointing down? The cylinder end should point *up* in relation to the large chamber end, to aid bleeding. The valbe should also be angled downwards for the same reason. MGBs seem to have them fitted horizontally and valve uppermost, but after-market instructions show them orientated as described. Both my MGBs have remote boosters and both those and two others I have worked on all need a 2-stage bleeding process - first filling and basic bleeding using low pressure from an EeziBleed, then high pressure from someone pressing hard on the pedal while I rapidly open and close each caliper nipple in turn, which always gets an extra lump of air out. Before the 2nd stage the pedal is long but pumps up, only to sink again if released for a few seconds, afterwards they are fine. Whether this is an effect of the booster, and its horizontal and 'valve up' positioning on both my cars or not I don't know. A booster will always result in a slightly spongier pedal than no booster, some people prefer them without for that reason. If your brakes locked in your scary episode, then the booster isn't going to stop that happening, in fact it will make it more likely. I had a clonk getting more noticeable on my V8, both heard and felt at the pedal. After some time spent investigating the front end during which I found both track-rod ends badly worn that the annual test hadn't picked up, I found it was one of the rear brakes causing it. Boosters wheeze and clank a bit when operating, particularly when pressing the pedal with the engine just having been switched off. If you are not used to that maybe that is all you are hearing.
PaulH Solihull

This thread was discussed on 17/12/2010

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