MG Car Repair: MG Midget brake bleeding and seizing, rear brakes, brake shoes

Question
QUESTION: I’ve had my 77 Midget for 16 years, most of that time it was a daily driver and have done most of the repair work myself. What follows began not because of any major problem, but just as a maintenance upgrade.

Recently I installed new rear brake shoes and cylinders and bled the system with no problems.

Several weeks later I began to take on air in the brakes and the front left caliper seized this seem to be due to a bad hose. So I purchased a front brake kit (both sides) and had a local brake shop do the work. They replaced pads, rotors and hoses, but said there was no need to rebuild the calipers because they were working fine. When I got the car back the brakes worked ok, but the pedal was at the very top and extremely hard.

A few weeks later I started to loose brakes i.e. the pedal got closer to the floor and wouldn't pump up. I installed a new master cylinder. The rear brakes would not bleed. The pedal went to the floor and only a bit of fluid dripped from the bleed screw and no sound of air (both sides). The front brakes were easy to bleed and the brake pedal goes half way to the floor where the front brakes take affect.

While trying to decide what to do, I drove the car around the block a few times and both front cylinders sized. After sitting for a time they released.

I spoke to an MG Tech. and he said:

Check that the rear metal lines are not crimped (I had the car towed once). They are fine.
If I can bleed the front calipers that indicates they are most likely OK.
I asked if the pressure differential warning valve could be a problem and he said not likely.

So that seems to indicate to me that there is a problem with the new master cylinder. Sorry about the length, but am quite frustrated. Would appreciate any help.


ANSWER: Hi Conrad,
When the both front calipers were locking up, you should have done a test. All you had to do was open a caliper bleeder valve to see if they would release. If they would release, then it was for sure a master cylinder or brake pedal problem. When a brake pedal is released all the way back a port is opened from the master cylinder (both circuits) back into the reservoir so it is impossible for any pressure to be on the calipers. If pressure is on the front calipers after the pedal is released then you know to correct the master cylinder and/or the pedal.
It sounds like that was your problem all the time.
Howard

---------- FOLLOW-UP ----------

QUESTION: Howard,

Thanks so much for the answer. Although I had not thought of the test you suggest, it makes sense to me now.

Would this also be the cause of the rear brake problem?

Thanks again.

Conrad

Answer
Conrad, I learned a long time ago to NOT try to figure out what all the problems could be because of this or that. I found the only sure way to correct problems was to test and only one at a time. Many times that one problem solved all the problems. This was true in diagnosis of mechanical or electrical problems.
A few times a mechanic can fix a problem by figuring out if it does this when I do this and it does that when I do this. But in a dealership where I was ONLY paid for a fix not work, I needed a 100% sure method of fixing cars with no wasted time guessing. Unfortunately many shops use the "Hunt & Peck" guessing method and the result is as many as 50% of all fixed cars that go out the back door have some parts on them that were NOT needed.
Howard