MG Car Repair: 1976 MG MIDGET 1500, rear shoes, cylinder problem

Question
FRONT BRAKES LOCK UP    NEW MASTER   CALIBERS DISASSEMBLED, CLEANED AND REASSEMBLED WORKING FIND   OPENED BLEEDER TO RELEASE PRESSURE   WHEELS MOVE FREELY  WHAT AM I MISSING TO CHECK

Answer
Hi JC,

The hydraulic system should have a free flow from any caliper or wheel cylinder to the master cylinder reservoir when the brake pedal is back.

You did the first test by opening a bleeder and that relieved the pressure. However, you skipped the second test. Pump the brakes up until you confirm that the brakes are dragging again. Then loosen the line (from the calipers) going into the master cylinder. If that relieves the pressure again then you for sure have a master cylinder problem. If it does not relieve the pressure then you have a stoppage between the master and the caliper. Swelled shut flex lines or a bent steel line.

Several things can be wrong with the master cylinder, even if you just replaced it. Check the free play in the pedal (should be about 1 inch).
Pump the pedal up again and confirm that the brakes are dragging again and this time open a bleeder on the rear wheel to see if there is any pressure there too. If there is pull the hand brake up and pump the pedal up again and confirm that the front brakes are dragging and open the rear wheel bleeder again. If there is pressure it confirms a master cylinder problem but if it does not have pressure it does not mean that you don't have a master problem.

Sometimes a out of adjustment of the rear brakes can cause pressure on the caliper. The rear shoes have strong springs and when you lift off of the brake pedal the shoe springs force the piston in on the wheel cylinder and that forces the fluid back to the reservoir but if the small hole is blocked in the master between the rear brake system and the reservoir the pressure will force the piston against the piston for the caliper and apply pressure. That is rare but a stone that must not be left unturned.

Howard