[moontower69]

Anybody had this issue. I had it looked at and mechanic said it was the E-brake locking it up. He disconnected it and it solved the problem but now it's back, the right rear locks up on light braking, feels dangerous.

I've replaced the cylinders and adjusted them. But keeps locking up. Do I need a new drum and kit?

Car is a 1974 Lemans Sportcoupe with factory discs in the front.

[leeklm]

I have experienced that issue when a rear wheel bearing was leaking. Would get just enough grease on brake pads to make them sticky, thus locking up on a low traction surface like a gravel road.

Of course pretty obvious to a mechanic if the pads are contaminated, so am assuming this is not your issue. I would start with the basics such as new brake springs and hardware , refurbished wheel cylinder, etc.

Sent from my SM-G965U using Tapatalk

[Paul E]

Helped a friend fix this same issue on his as the rears would lock up really bad, especially when cold. After a lot of opinions of proportioning valve, someone installed a rear adjustable, time and money. I took the rears drums off and condition of everything. All looked very good visually but just the surface of the shoe material looked off. We changed the rear shoes and adjusted them to the proper drum diam, scuffed the drum bu hand with mild sand paper (even wear on drum present) and issue went away. This was a few years ago and problem never returned. try just doing a shoe change with lube on the pad to backing plate bosses etc and likely the solution with little money out of pocket.
If leaking axle seal, when cylinder, rust, broken spring, way out of adjustment, or other issue found with drum off that would be the problem....
Paul

[Chris65LeMans]

Proportioning valve controlling front vs. back?

I'm not sure how it would have been the parking brake.

[1969GiPper]

Originally Posted by moontower69

Anybody had this issue. I had it looked at and mechanic said it was the E-brake locking it up. He disconnected it and it solved the problem but now it's back, the right rear locks up on light braking, feels dangerous.

I've replaced the cylinders and adjusted them. But keeps locking up. Do I need a new drum and kit?

Car is a 1974 Lemans Sportcoupe with factory discs in the front.

Check to see if the shoes were put on correctly. Primary shoe towards the front and secondary shoe towards the rear.

[moontower69]

Gonna try to replace the shoes, I already fell for the "oh its def the proportioning valve" from my local tire shop mechanic and $300 later it fixed nothing. Maybe they're warped or something that's not visually apparent.

[Sirrotica]

To test for warped rear drums, apply the emergency brake at low speed and slowly bring the car to a stop with just the emergency brake. If the drums are warped it will pulsate just before coming to a stop. Usually this does not cause a wheel to lock up.

As has been mentioned linings contaminated with either brake fluid or rear axle lube will grab.

Incorrect self adjusters installation will continue to adjust going forward, correct operation they only adjust going in reverse as the brakes are applied. One side has a right handed thread the other the left handed thread, they have to be on the correct side so they work properly. Turning the outside of the star wheel down, should lengthen the adjuster if they are installed correctly.

[Chris65LeMans]

Originally Posted by moontower69

Gonna try to replace the shoes, I already fell for the "oh its def the proportioning valve" from my local tire shop mechanic and $300 later it fixed nothing. Maybe they're warped or something that's not visually apparent.

I didn’t mean replacing it, I meant adjusting it.

[Geoff]

When just one side does it, it suggests an imbalance. Could be a few things:
- out of round drum. Might be only slight & might not be felt. Swap L & R drums as a test.
- weak brake shoe return springs, causes linings to drag, build up heat, changes lining characteristics, you get lock up.
- rusted wh cyls can also cause slow shoe retraction, dragging, above.'
- any contamination on the shoes
- different linings side to side, different friction characteristics.
-or....sometimes the manufacturer gets it wrong & certain models get a reputation for brake lock up. Not sure about your model. On my GTO, with factory wheel cyls, I didn't like the way the rears locked up at low speeds. I fixed it by having the rear wh cyls sleeved for a 1/16" smaller diam piston.

[Scott Thelander]

rubber flex hose breaking down ...

grooves in the backing plate from power brake burnouts...

moody wheel cylinder guts

a clue if its the adjuster is you wil have a real hard time getting the drum off

Scottt good luck