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MG MGB Technical - Help, no brakes.

Hi guys,

I've been having some trouble with my brakes and thought you might be able to help.

The car is a '76 B.

About a month ago I got in the car and even before starting it put my foot on the brake pedal which went straight to the floor - no resistance at all. I checked the fluid resevior and it was completely empty. As I had it booked in at a garage anyway for some other work I just topped up the resevior and pumped the pedal a bit (didn't bother bleeding the system or anything) and drove very carefully to the garage.

They fitted a new master cylinder and it was all fine.

About 3 weeks later, got in the car - same thing, pedal goes straight to the floor with no resistance. So i thought I repeat the process as above and try and get the garage to look at it again.

This time though, as I added fluid to the resevior (it was emtpy again) I couldn't get the brakes to work even at all. Then, as I was pumping the pedal I heard a gurgling noise form the servo (separate unit on other side of bonnet). It gurgled each time the pedal was pressed and that's all that happened.

I did have a look arounf the car for signs of leaks at each wheel, but couldn't see anything. The car lives outside at the moment though so any leaks might not be so evident.

Any ideas? I'm espcially keen to hear about ideas that don't involve the servo needing replacemnt as these seem to be about £400 new.

Thanks in advance,
George
G Kerr

New servos are only around £150 and a seal kit is £50 or so.
Chris at Octarine Services


George,

Well, I don't see how a bad servo would make the fluid from the MC disappear. I've had several B's that would lose brake fluid but I couldn't find out where it was going (until I took the MC off and found fluid leaking into the servo!) Could it be that you got a bad replacement MC and it's leaking back into the servo? You can easily tell if it's leaking at the rear wheel cylinders as the lower inner part of the tires will be wet. I would check the MC first though.

BTW, rebuild kits are availble for those servos for around $50 USD. I redid the one on my '77 B due to a vacuum leak. Not much in there besides a big rubber diaphragm and a spring I think.

Good luck,
Dave
Dave Plantz

A bad servo can cause brake fluid to be sucked through it and into the inlet manifold and burnt, for the remote servo anyway. But make sure there aren't any leaks from the remainder of the hydraulic system before thinking any more about the servo.
Paul Hunt

Thanks for that,

It'll be next weekend before I can get a proper look in the daylight.

I guess there must have been some sudden complete failure as the brakes were fine.

The thing that's new to me is that replacing the fluid doesn't do anything. With other brake problems I've seen, topping up the fluid normally gets some limited braking action going.

Anyway thanks again,
George
G Kerr

Remove the servo and make up and fit a short right angled brake pipe with the correct flares and fittings to fit between the two vacant connections. Bleed the brakes and run the car. I too am fairly sure that the servo needs rebuilt but running it without will prove the point. Remember that servos were not standard until the 1972/3 year so there is no harm in running without. The pedal effort will be slightly greater but not that much as the servo ratio is only 1.6/1. Don't forget to plug the vacuum hose otherwise the engine won't run.
Iain MacKintosh

This thread was discussed between 12/12/2004 and 14/12/2004

MG MGB Technical index

This thread is from the archive. The Live MG MGB Technical BBS is active now.