L-R wheel locked after short drive, then free after rest. Brake shoe getting stuck?

[BrianK]

To summarize: I think one of my rear brake shoes is somehow locking the drum after a short drive. I’m not sure if that’s true, or how to fix it. 
 

Here’s the story:
 

My last real drive was about 100 miles - no problems. after that drive, I drove to my storage shed & left it there for a couple weeks. Came back to drive around the block, which I did successfully (2-3 miles), but after I parked the car for about 10 minutes while I rearranged the shed, I reversed a few feet, then when I tried to go forward, I only made it about a foot before the car stopped and wouldn’t move any further - like something was stuck. 
 

I tried reverse again… several feet, no problem; then forward… 1-2 feet then stop. I almost felt like I could goose it to get it to move, but I decided against that. 
 

I shut it down, took it out of gear, then pushed the car backward - no problem, then forward and stop.  …a hard stop. 
 

I jacked up the rear end i could freely move the right rear wheel back and forth, but the left rear wheel was exhibiting the problem behavior… reverse, ok; but forward = lock. After the lock, the wheel would be hard to move backward, but after a few inches, would free up and move backward easily. Importantly, however, once I hit the “lock” position, if I moved the wheel back just a few inches 2 or 3 times, I could then go forward again - maybe 3/4-1 turn, then it would lock. 
 

There was no moving the car at that point - I had to put the rear tires on wheel dollies to get the car into the garage. 
 

That was a couple weeks ago. Today, I got some time to diagnose. After jacking up the rear end this time, I can freely move the LR wheel forward and backward. It’s a little sticky in one spot, but otherwise moves fine. 
 

I’ve just removed the axle and drum from that side, and am able to freely rotate the stub (the bit of axle in the diff), the other wheel, and the input shaft - nothing seems to lock/stop & all are perfectly smooth. There’s fluid in the diff and trans (both of which have been rebuilt within the last 500 miles). This makes me think that the problem must have been related to the drums. 
 

This is the only car I’ve ever owned or worked on that has drum brakes. With that, questions:

First and foremost, what should I do?

Is it plausible that the brake shoes are somehow getting caught inside the drum? Maybe going in reverse moved something that then got hung up when I went forward?

Could I have installed the drum off center? I installed these drums after having the diff rebuilt. My method was to put them on and screw the axle UJs in - I didn’t do any sort of alignment. Granted, that was about 500 miles ago, and this is the first time I’ve had this problem.

Is it ok for the shoes to have a bit of vertical play (video below)? If not, how to fix?

Any ideas on prevention?

Am I safe to drive the car?

if this happens when I’m not at my garage, how do I get moving again?

 

 

Showing the “lock” when pushing forward. Note how difficult it is to move back - maybe the brake is still somewhat stuck?

 

[ramjet]

What you have described fits with the way that drum brakes are set up. Drum brakes can be set up two ways. One way only has one slave cylinder in the drum that operates both shoes (cheapest & lightest). The other way has two slave cylinders that operate the shoes (more expensive & heavier). The second way is better as you have two leading ends on the shoes vs only one leading end and a trailing end in the single slave setup. However, as I said it is more expensive and heavier, so unlikely that Lotus went with this.

What you have suggests that the shoe/s are jamming going forward as the trailing end/s get pulled toward the drum and lock it up. Moving the car backwards, pushes on the trailling end/s and moves the shoes away from the drum enough to let you move the car.

I have just been able to find a drawing of the Eilte drum setup. It is still possible to have the symptoms you are relating with a single slave cylinder setup. Only a single shoe is most likely causing it to occur.

Either way I would suggest that you have either a mis-adjusted slave cylinder in the hub which is unlikely as you haven't touched that, or the slave cylinder piston has seized. Sorry, but that is the most likely.

[ramjet]

Oh, I meant to say,

My apologies to all of the silly people at Jaguar who consider the use of the word slave in this case to be derogatory.

[EXCEL V8]

As Michael says the rear brakes are a single leading shoe set-up.  It it normal for the shoes to slide vertically - it's what allows the whole surface of the shoe to make contact with the drum. 

The first thing to check is the normal operation of the slave cylinder - get someone to press the brake pedal and watch the piston to make sure it retracts all the way.  The piston doesn't slowly come further out to compensate for wear like a disc brake - the slave cyl piston should retract completely each time it is operated.

  Next check that the handbrake mechanism is releasing properly and that the automatic adjuster is working within the drum and not seized.  The slave cyl is also free to slide on the backplate - make sure it can. 

When you reassemble the shoes put a good chamfer on the leading edge of the friction material - it helps stop them grabbing;  the leading shoe exhibits a self-servo action in operation and the chamfer helps this come on a little more gently.

Let us know what you find!

Pete

[pbharcourt]

I had a similar problem and it was one of the springs that hold the brake shoes together had snapped, this allows the drum to move happily in one direction but the shoe catches in the drum in other direction.

[BrianK]

I'm always impressed by the collective knowledge of the people who visit this forum.   

I know where to look at what to test now. Thank you.

I'll keep the thread updated as I find answers or more questions.

[BrianK]

As suggested, the wheel cylinder is sticking.  I’ll have a new one on order as soon as I get back to the house. 
 

 

Thanks again, fellas. 👍

Edited July 3, 2022 by BrianK

[EXCEL V8]

The wheel cylinders were originally available in different diameters - one for the manual cars, one for automatics.  The only one available over here is the automatic version.

Pete

[BrianK]

1 hour ago, EXCEL V8 said:

The wheel cylinders were originally available in different diameters - one for the manual cars, one for automatics.  The only one available over here is the automatic version.

I recall reading about that, but not the details.  One has 7/8" bore and the other 3/4", is that right?  

Looking through receipts for my car, I see a wheel cylinder was replaced in 2004 with a 7/8" bore model. 

SJ only has 3/4" bore wheel cylinders, so that's what I ordered.  Should I have ordered 2 and replaced both?

[EXCEL V8]

8 hours ago, BrianK said:

I recall reading about that, but not the details.  One has 7/8" bore and the other 3/4", is that right?  

Looking through receipts for my car, I see a wheel cylinder was replaced in 2004 with a 7/8" bore model. 

SJ only has 3/4" bore wheel cylinders, so that's what I ordered.  Should I have ordered 2 and replaced both?

Yep - 3/4" for the auto and 7/8" for the manual.  I'm not sure you'd notice any difference while driving.  I would replace both since you may have to drop the diff to do the work.

Pete

[ramjet]

I would definitely be replacing both. The imbalance between the rears would not be very noticeable, but better safe than sorry.

[BrianK]

19 hours ago, EXCEL V8 said:I would replace both since you may have to drop the diff to do the work.

Oh, I hope I don’t have to drop the diff. While I’m getting good at it now, it’s at the top of the list of “least favorite jobs”. 😛 

[BrianK]

So that it's known: you do, in fact, have to remove the diff to replace wheel cylinders... either that or cut large holes in the body under the rear seats (and even then, you might not have enough access)

If anyone Googles their way here: be sure to get replacement retaining clips for the wheel cylinders. You might also want new dust boots.

The rear hard brake lines need to be capped while you do this job. The hard lines have the female end, so you'll need male plugs. I thought I could cap them with bleed screws, but they were too long, so I ended up getting a brake master cylinder bleed kit from the local auto parts store. It has several plastic male ends of various sizes - each with a barbed fitting that can be plugged. A couple ends in the kit fit well enough to stop fluid from flowing out of my hard lines. I don't think they were the exact correct size, but they were plastic, so I treated them as sacrificial and just forced them in (they are not visible in this picture).

 

There is, of course, a story that goes along with this picture, but I'll save that for my project thread.

While I have gotten better at gaining access to and removing the diff, I still ran into snags - turning removal into an all-day affair. Unfortunately, because of my schedule, I probably won't get back to reassembly until September. :: sigh :: 

Have I mentioned how much I dislike removing the diff?   

 

[BrianK]

On 16/08/2022 at 10:59, BrianK said:

If anyone Googles their way here: be sure to get replacement retaining clips for the wheel cylinders. You might also want new dust boots.

Another update related to this: The replacement retaining clips I got were made of thinner metal than those that I removed.  So thin, in fact, that they didn't "latch" as well as the old ones, so I ended up reusing the old ones.

[Gray14]

I have a spare differential with rear brakes that I’ve just been cleaning, and looking at the backplate and slave cylinder, it looks as though the cylinder is designed to slide along the slot in the backplate to exert pressure on the rear brake shoe once the piston has reached its maximum extension on the front brake shoe.

When the piston extends the shoe against the drum to the front and it can’t extend any more it looks as though the continuing pressure inside the slave cylinder is expected to slide the slave cylinder backwards to bring the rear shoe into contact against the brake drum.

If the slave cylinder cannot slide either backwards or forward in the backplate slot, then the shoe is not going to make contact or get stuck against the drum, locking it up.

This would explain the 2 retaining plates to the back of the slave cylinder, and why a much simpler, more conventional bolt fixing is not used.

It also explains the use of flexible brake pipes to the cylinders and why the 2 bleed pipes are routed to rotate about a fixing on the bottom of the diff cover to avoid the use of flexible pies here too.

I’ve noticed these cylinders were fitted to numerous cars in the early 1950s including Nash Metropolitan, Jaguars and Austin-Healy’s, and it seems to be a way to get a single slave cylinder to exert force in 2 directions.

Just checking the workshop manual, section J.7, Braking System, page 10 ‘To Replace’, and it says to grease the cylinder aperture in the backplate with Girling white grease, and later, check that the cylinder is free to slide in the backplate.

I think that explains why my handbrake is not very good. A not very accessible place that requires a lot of maintenance.

[EXCEL V8]

Yep - that's exactly how they work!

Pete

[BrianK]

On 22/09/2022 at 15:35, BrianK said:

Another update related to this: The replacement retaining clips I got were made of thinner metal than those that I removed.  So thin, in fact, that they didn't "latch" as well as the old ones, so I ended up reusing the old ones.

As a follow-up and to keep the quality of archives here high... I was incorrect in assuming the retaining clips should be snug.  As @Gray14 pointed out, the wheel cylinder is meant to slide back and forth in the backing plate, so, in fact, you want it to be retained as freely as possible without losing the clips. So the replacement clips I mentioned here may have actually helped in my case.

I also found that the bleed extensions - which are hard lines on my car - can be routed ever so slightly incorrectly so that they are putting a force on the wheel cylinder that prevents it from sliding (or at least makes it more difficult to slide). It's easy enough to bend the line as needed to ensure that the wheel cylinder has free fore/aft motion. I simply pushed the line in one direction, tried to slide the cylinder back/forth by hand, then pushed in a different direction, & tried again (and repeat) until the wheel cylinder moved as freely as possible.

At the end of the day, the problem that started this thread was the result of a variety of issues, the most egregious of which was out-of-round drums.  More info here: