Rear/unpowered shoe binding/not returning - causing rear wheel to lock when braking

[BrianK]

Background:

Not too long ago, I had no rear brakes on account of a very leak differential.  Since fixing the diff, I've been running into rear brake problems (which were probably always there, but I never noticed until the brakes actually started doing something).

Previously, I'd found that one of my wheel cylinders was sticking, so I replaced both wheel cylinders. I completed that job in September, then drove about 100 miles without issue. I then put the car in storage until last weekend.  The first couple stops out of storage went fine, but then I started noticing the rear brake sticking again. By the time I got home, it was a real problem - the left-rear would lock as I came to a stop. Sometimes it would release on its own, other times I had to back up a couple inches, and on a couple occasions, I found that tapping the brake pedal freed it.

Problem:

I verified that it's the left brake that's sticking. No problems with the right. I rolled back the parking brake adjustment to make sure it wasn't an adjustment problem. I verified that the wheel cylinder can move fore/aft. I double-checked that the cylinder and shoes had white lithium grease between them and the backing plate; but I haven't been able to stop the brake from locking/binding when coming to a stop.

Today, I made a video of the problem & hope someone can offer a suggestion for fix, as I'm running out of ideas:

In this video, I partially blocked the front shoe because I was interested in what the rear shoe was doing. You can see that the rear shoe is not returning as quickly as the front.  I think this is my problem, but I don't know how to fix it.

I suppose one option is to use thinner retaining clips on the wheel cylinder (the replacement clips I got were thinner than stock, so I opted to stay with the stock part because I didn't realize the wheel cylinder was designed to slide back and forth, so was looking for a more snug fit).  This is something I'd *really* rather not do as it involves dropping the diff. Any tips on this - that don't involve dropping the diff - are greatly appreciated.

Another option might be to load the retaining clip with grease. I'll admit, I don't think I greased the back of the backing plate - I only greased the front/outside. Not quite sure how to do this with such limited space. Again, tips appreciated.

Another option might be to try a newer spring between the shoes - maybe mine is so old that it's lost some of its spring force? (the date stamp says either 1983 or 1993 - it's hard to read. either way, they are old)

Thoughts on these options? Other ideas? Maybe I'm barking up the wrong tree entirely?

[EXCEL V8]

Is the back plate completely flat where the brake shoes sit?  Mine had worn a ridge that needed grinding off to provide a flat surface again.  ISTR there were 3 flat slightly raised areas for each shoe.  How flexible is the brake pipe connected to the cylinder - is it copper (or steel etc..) or flexible hose?

Pete

[BrianK]

To answer your questions:

Is the backplate flat where the shoes sit? Yes. To be sure, today I cleaned off the 3-per-shoe contact spots, then ensured flatness by running a finger sander over each spot until the metal was shiny smooth. I then re-greased them before reassembly. Interestingly, one of those spots did have a nick, but it was for the front shoe - one that seems to have always worked as expected. Regardless, even that one is butter smooth now.

How flexible is the brake pipe connected to the cylinder? Flexible line between cylinder and hard line that goes to the front; hard line between the cylinder and the bleed valve that lives on the bottom side of the diff. Today, I made an adjustment to that bleed valve hard line, only to find that the cylinder would NOT slide when the line wasn't adjusted correctly. With that knowledge, I bent the hard line until I had very easy movement on the wheel cylinder - much better than it had been before today. To be absolutely certain, I disconnected the bleed valve from its chassis mount so that there was no way it would interfere with the wheel cylinder sliding. I really thought this would solve the issue (spoiler: it didn't)

I also absolutely loaded the wheel cylinder mounting location with lithium grease - so much that it was coming out all around the wheel cylinder dust boot. I also slid the cylinder fore/aft probably 150-200 times to work the grease into place. It was relatively easy to slide.

I then verified that the re-centering of the left shoes were on par with those of the right shoes by taking video of both sides.

Even with that, after putting everything back together & spinning the wheel in the air while someone else lightly rode the brakes, I could get the shoe to stick.  To confirm, I did another drive around the block & the binding persists.

I've been chasing this problem since June. I'm still open to ideas if anyone has one, but I think it's time to throw in the towel.  I'm going to call a specialist in the morning. 🤬

I'll report back when it's sorted in case anyone else has the same experience.

[EXCEL V8]

I can't quite see from the video - are both leading edges chamfered?  Is the little "H" - shaped piece in there?

Pete

[BrianK]

Both leading edges are chamfered. I did this just last week. Granted, I say "chamfered," but they are more beveled - a round-ish edge because I'm not very precise with my file. Don't know if that matters?

The little H-shaped piece is not there.  Never has been.

To further the story: the specialist I normally use is backed up until late January, so I'm back to working on it. They asked if I'd had the drums turned or shoes replaced - I haven't. So, as a next step, I'm going to replace the shoes, all the springs, re-introduce the H-shaped piece and have the drums turned.

The saga continues...   

[BrianK]

While there's still work to do, initial tests seem to show that the locking problem has been solved. 

First principles and all... I think the primary problem was out-of-round drums. They certainly made some rhythmic noises while being turned.

I also believe the springs between shoes were old. I replaced them as well, and the new ones are 3-4x stronger/stiffer.

To be thorough, the shoes were also replaced.

While at it, I added the H-shaped spacer between the parking brake lever and shoe. I don't think it was related to the initial problem, but it should make the parking brake more effective.

I still need to do a proper bleed and get some real heat into the brakes, but, as of today, all signs are pointing to the problem being solved.

Thanks for all the input.

Edited January 7, 2023 by BrianK