VCCA Home Forums TECHNICAL - GENERAL Mechanical - Engine, Trans, etc brakes

36 had all new shoes wheel cylinder lines done drove 2 weeks master cylinder leak put a new master cylinder on now everthing fine i throught drive 20 miles pedel get tight back wheels get hot front ok back brakes lock up let set till cools down ok for 20 more miles why does it not tight till driven then coo;s down it ok what make it get tight but is ok when starting out right rear is real hot and tight left a little hot both front cool and fine would t they be tight all the time if adj to tight why loose then tighten up set then loose up drive get tighrt again i give up thinks smitty

Loosen up your emergency brake cables and recheck if rear loosen up.

i don t use emergency brake that was my throught to but how does itseem to tightent up on it own then release after itcools downit ok start out but get tight after driving and i don t touch the emergency brake at no time how does it move on it own brake pedel get tight with no play cools down pedel has play and unlocks my it self still have not touched emergencybrake

The emergency brake can apply it self if it was not re-adjusted after installing new brake lining. There is an eccentric bolt on the end of the brake shoe near the wheel cylinder inside the brake housing and the adjustment procedure is in the shop manual. Other problems can cause a dragging brake include weak return springs, the lower eccentric links tight from corrosion, wheel cylinders that are sticking from swollen piston boots. A brake can apply itself is it is adjusted to tight as the shoe/lining will expand slightly as the heat builds up applying the brake.

It sounds like the small vent in the master cylinder is plugged. When the brakes and fluid get warm they expand and the fluid has nowhere to go. The little vent is like a pin hole in size and maybe you can get to it from to top of the cylinder. If not, you'll have to remove the cylinder and disassemble it....

It appears the locking brake problem started after you replaced the master cylinder. I had a situation where I rebuilt the master cylinder on a 1950 Chevy pickup that leaked. The leak stopped, but the brakes would lock up. Using the brake pedal would cause the brake shoes to push against the drum, but the shoes wouldn't return to their original position after the brake pedal was released. After reviewing the master cylinder rebuild in my mind, I remembered I reused the original spring and "stretched" it out a little to account for all the years it was compressed. I didn't realize it at the time, but by stretching the spring, I upset an important pressure balance designed into the brake system. I installed the replacement spring that came with the master cylinder kit and all has been well for 30 years.

Possible cause-
Brake pedal has no frre-play and the brakes are slways slightly applied. Free-play is adjusted by turning the eccentric bolt just in front of the master cylinder push rod shaft. Pedal should have about 1/4" toe board clearence.