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MG MGB Technical - Very soft brakes

Hi folks,
The brakes on my 73GT have gone extremely soft - pretty much overnight. The pedal travels almost to the floor, but if I pump the pedal quickly a couple of times, they will stop the car.

Based on my VERY limited mechanical knowledge, I checked the brake lines to the front discs. No sign of a leak. I need to take off the drums this evening to get a look at the back.

If it's not a leak (there didn't appear to be any signs of a leak on the driveway), then what else could be causing this?
Mark 73BGT

Mark, if you have no leakage and your brakes suddenly go "soft" I suspect your have a master cylinder that has failed internally. Replace that unit a.s.a.p. and completely bleed the system with fresh brake fluid. You should be back to normal after that.

Let us know what the outcome of your problem is

cheers

Gary :>{D
gnhansen

Thanks Gary...I suspected as much, but wasn't sure if there were potentially other causes too.

I checked on the MGOC UK parts list. I can get a repacement master cylinder @ stg£170, but there is also a master cylinder repair kit @ stg£35.

Does anybody have experience of using the repair kit. What are the disadvantages vs replacing the whole master cylinder (which I'd like to avoid if possible from a cost perspective)?
Mark 73BGT

Mark, I am surprised by that price. I recently bought a new master cylinder for the same reason. It cost much less from Midland Sports and Classic +44 (0)1905 621331. The new ones come with the latest plastic resevoir so you can see the fluid level more easily.
David Witham

Thanks for the heads up David - I just called MGOC to confirm the price. The £170 unit is for later rubber bumper dual circuit cars. The agent told me that the units for my car is only £40.

Just goes to show - always check here first!

Thanks all.
Mark 73BGT

Mark

Another possibility is a leaking rear cylinder - not readily visible until you have removed the brake drums. My 73B had the 'pedal to the floor' sympton on taking the car out of winter storage. The problem proved to be a leaking rear cylinder - I assume that the seal dried out due to lack of use. If you have to replace a cylinder, consider using a 5/8" circlip to retain it in place - much easier to install than the dreaded 'E' clip about which much has been written on this BBS.

Good luck.

Barry
73B
B.J. Quartermaine

I took the hubs off the back & checked the rear seals - no probs there (although the adjusters had seized, so I oiled & loosened them up).

Just to eliminate the obvious, I bled the brakes before. It turns out there was air in the system (front passenger side). Everything seems to be fine now, so I'll keep an eye on it to see if it sucks in any more air.

Thanks everybody for the input.
Mark 73BGT

This thread was discussed between 27/07/2005 and 03/08/2005

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