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MG MGA - Brake issue

I am having brake problems with respect to my 1962 Mk II. Pedal travel wound up closer to the floor than I would like, and brakes felt spongy. Both shoes and pads were replaced and the system was bled. The car performed satisfactorily until the next morning, at which time the pedal traveled nearly to the floor and the brakes were much worse than when I started. We next used one of the compressor devices to bleed from each brake nipple, and the pedal pressure and braking was outstanding. However, this morning the pedal again traveled to the floor with virtually no brakes. Brake fluid level has remained constant, and was replenished during bleeding. No leaks apparent anywhere, and (by the way) the rear brakes were properly adjusted. Seems logical that somehow air is getting into the system overnight? In any event, your help is appreciatd. Catesby
Catesby Woodford

It could be master cylinder seals letting fluid past.
Dan Smithers

can you pump them up with the pedal?

Given that this sounds like a leak, my guess would be a leak inside one of the rear drums at the slave cylinder - maybe it's just not obvious that it is leaking.

I had an issue with a leak at the point where the hard line connects to the rubber line at the rear near the battery tray. It doesn't take much of a leak at any one wheel to make the system go spongy.

Good luck!

AJ Mail

If air were leaking in then almost certainly fluid would be leaking out. If the M/C seals were letting fluid past then there would most likely be a leak from the front of the cylinder. It could be the non-return valve in the M/C though. It is on the end of the spring on the brake push rod and is supposed to retain the brake pressure (I think). Either way it needs the M/C refurbishing with new seals IMHO. Good luck
Cam Cunningham

A seal leaking in the master cylinder will not necessarily allow any fluid out. The fluid leaks past the main seal but it can be kept in the cylinder by the secondary seal. This seems to be quite a common failure mode. Air trapped in the system might give these symptoms, but no way, or reason for air to get in unless there is a leak, in which case the fluid level will drop. One way to check is to pump the pedal up and then hold the pressure and see if the pedal starts to move. Sometimes the pedal can stay firm until you think everything is ok then suddenly move 1/4" or so!
N McGurk

Thanks very much for all the good advice. Last night, we attached a pressure bleeding device to the master cylinder side (using an air hose attached to the tire), and observed absolutely nothing in terms of hissing or leaks in what would thus appear to have been a pressurized system (for an mg, anyway). I then bled the system (for the third time) using that same system (this time with fluid in the bottle), and the brakes are firm. Trouble is, this has happened twice before -- firm brakes, followed by a drive, followed by nothing the next morning. So, I aim to drive it later today, park it at a friend's shop (which has a lift), and change the master cylinder. I'll report as to the results and, again, am grateful for the help. Catesby (Kentucky).
Catesby Woodford

This thread was discussed between 30/04/2012 and 01/05/2012

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