VCCA Home Forums TECHNICAL - GENERAL Mechanical - Engine, Trans, etc '31 brakes lock

What would cause the rear brakes on my '31 coupe to lock up in reverse? It happens backing out of the garage, and I have to pull forward a foot or so to release them. Usually the next time I back up and hit the brakes while still in the driveway, they grab. But the next time I hit them in reverse, they seem to be okay. This hasn't been a problem until I trailered the car to the Petit Jean Show a couple weeks ago (about 200 miles), and they locked up while backing off the trailer. I had to pull forward and back up a little, pull forward and back up a little, until I got it off the trailer. Any thoughts? I remember that I turned one of the drums a little past its tolerance when I restored the car about 3 years ago. Could this be the problem?
Thanks,
Sid

My thoughts - rust in drums, weak pull back springs, brake shoes not centralized, cross shaft not rotating completely.

This has been a problem some of us have had and previously discussed without a definitive answer. I did find frozen link pins on my 32 and after freeing and lubing it seemed to be fine, however a year later the problem has returned. I have not had it apart again, but I find it hard to believe they are frozen again. With tight pins just the cam end of the shoe was contacting the drum. When in reverse the shoe/drum contact was enough to unseat the frozen pin allowing full contact and still a frozen pin so when letting off the brake the return spring does not have enough tension to release the shoe. Sure is fun getting it off the trailer without using the brakes!!! If the drums are turned past the limit the lining could be shimmed an equal amount and then the shoes arced to the proper contour

Hi Chipper,

If you could elaborate on the cross shaft not rotating completely I would appreciate it. I know my cross shaft is questionable (ctr. bushing) and I am waiting for a used one to arrive that I will rebuild. My thoughts are that if the brake pedal returns to its stop then the cross shaft is rotating properly.

I hope I can explain this correctly. The '31 cross shaft rotates in the outside supports and also in the near center support. Each of the outside supports also rotate forward and aft. Therefore a rear brake shoe doesn't have to fully release for the pedal can come back to its stop.

OK. I think I understand that explanation, but don't feel it's the cause of the brake lock. All linkages from the pedal up to and including the camshafts are releasing. I can back out of my garage and when the brake locks it's like pulling the emergency brake. I've even jacked up the car after it has happened and its impossible to turn the wheel(rh front but varies) backwards. Move it an inch forward and everything is fine. It is without a doubt the shoe locking into the drum and when it happens its like putting a powerglide into park while moving.

Thanks for all the responses guys. m006840 has the same symptoms I have. I'm going to check the springs first. I bet I chose not to replace them during restoration. I'll let you know.
Sid

I have the same problem with my 32....when backing up first thing in the morning. Once I drive about a mile then no problem until the next day. It stated on the right side front and after new king pins its now on both fronts. I tried new springs with no results. I'm going to try and center them next and hope that helps.

Be sure to check that the front link pins and links are free first. If they are tight or frozen the shoes will not move evenly and it will be impossible to centralize the shoes. The shoes need to fully contact the drums to properly centralize.

I'm still thinking brake shoes are not centralized. Therefore one shoe is too close to the drum. When drum is cold it's tight, once the drum expands a tad from heat it is loose enough to not drag.

I had to move my 32 out of the garage yesterday. My retired restoration shop friend was present so I thought it would be a good chance to get an opinion on the brake lock when backing. I could not get them to lock. Tried several times and they worked fine (in reverse), still plenty of squeal when applying them going forward.

I finally got around to pulling a rear drum off my '31. The springs are new, and I centralized the system when I built the car about 5 years and less than 200 miles ago. The shoes look great, the drum looks great, and all moving parts seem to be free. I'm still puzzled as to what causes the brakes to lock. Any other thoughts?
Thanks,
Sid

I would completely disassemble the brake assy. to be sure all moving parts are actually free rather than "seem free". When the forward part of the shoe is raised by the link action there is very little movement of the pin and with the drum off it is a good time to verify movement.

I had a similar problem.

The cause was the small cam-shaft that is connected to the cross-shaft which ends in the differential housing. The problem is that the bushing that the shaft goes through at the backing plate, wears. And since the shaft is in a fixed position and only rotates a little bit, then it ALWAYS wears the bushing at the same spot EVERY time that you step on the brake.

So the end result is that the bushing opening becomes egg-shaped (slightly oval instead of round). Depending upon the amount of wear you may NOT be able to see this elongation unless the car has over 80,000 miles wear on it. It will look round to the naked eye.

Then when you step on the brake, a) the shaft begins to turn slightly, and b) then it "shifts" dramatically toward the elongated area of the bushing. This causes the shoes to "jump" the last little distance to FULLY engage the drum. The shaft "locks" into position and the shoes "grab" the drum. When my car did this (in reverse) it would literally leave a skid mark on the pavement.

Now, here's the trick. You can SEE this in action. But it takes two people.

Assuming that it's the rear brakes that lock up.....

1) Raise the left rear wheel off the ground. Remove the tire. Remove the drum.
2) Person 1 starts the engine. Put it in gear and slowly speed it up a little bit. (Since the right wheel is on the ground, it won't rotate. Only the left drive shaft will turn.)
3) Now with only a low speed revolution, step on the brake quickly.
4) The second person needs to be on their knees closely looking at the brake cam. What they "probably" will see is that the cam will rotate and then "jerk" slightly as it moves into the egg-shaped bushing.

Do this a couple of times at slightly different speeds. If the cam shaft moves in any direction other than a stable rotation, then it's the egg-shaped wear that is allowing the brakes to GRAB the drum.

The bushings are easily pressed out and replaced. They are the same as the brake/clutch shaft bushings that The Filling Station sells.

Good luck.

---Bill Barker

Thanks Bill. I've already got the right drum off. Will this process work from either side?
Sid

Also, I assume We are talking about the shaft for the service brakes which comes into the rear of each backing plate
Thanks,
Sid

Yes, yes and yes.

I checked the bushing in the backing plate and found no evidence of out of round or severe wear. I may end up replacing that bushing, but I thought I would check out other things first. I know that the brake drum is cut past tolerance. Does anyone have a source for a new or good used brake drum?
Thanks,
Sid

If the drum wear is causing the shoe adjustment to be at it's limit and the cam has little travel the shoe lining can be shimmed to compensate.

Thanks Steve, I may end up doing that too.
In my quest for drums, can someone tell me what the inside diameter of the drums was originally on a 31 passenger car?
Sid

Sid
If the brake drums are different diameters it will cause the larger 1 to be more efficient than the other.
Tony

Thanks Tony, for your information. Since I have one drum that is turned further than all the others, is a possible solution turning all drums to a similar size? My concern is that I would then have weaker drums, more subject to warping.

Have I stumped the panel? No one knows the original inside diameter of a '31 brake drum?
Sid

11 1/2"

Thanks Dog.
Sid

Sid
Until 10 years ago here in Aus you could get "oversize" brake linings that suited brake drums that needed to be machined beyond .060" over standard size, these linings extended the life of brake drums (upto .090" oversize) without problems providing each axle had evenly machined drums.
Tony