Left Rear Brake Grabbing

[Al and Missy]

Before heading out on our trip, I replaced all the wheel bearings and races. In that process I discovered a worn brake magnet on the left rear so I replaced both magnets on the rear axle and turned the magnet surface on the face of both drums. All the brakes shoes and drums were well within allowable wear limits and I didn't see any significant cracking on the shoes. I adjusted the brakes before heading out, and everything was fine for over 700 miles. On the way back, the left rear brake started grabbing at slow speeds. Everything appears normal above about 15-20 mph. Adjusting the controller for less current didn't affect anything.

Given that the brakes should have worn on the first part of the trip, I'd think that adjustment wouldn't be a problem, and I doubt that there is any grease on the shoes or drums because I was pretty meticulous about cleaning everything before and after re-packing.

I guess I'll be pulling the drum and inspecting the brake assembly. Other than the presence of grease and damage to the magnet or magnet surface on the drum, what else should I look for?

Thanks,

Al

[oldiesel]

Wish i could offer some advice as i have the same symptoms after about the same mileage from cleaning and adjusting brakes on my new axles.i believe it is the left rear that is grabbing but have not had time ti get into it yet. I will be watching this thread closley

[dznf0g]

I think you probably hit it here:
"damage to the magnet or magnet surface on the drum, what else should I look for?"

Grease typically doesn't cause grabbing.

Could have a shoe that came apart or sticking apply mechanism linkage...other than that, nothing comes to mind. Any electrical issue would cause the opposite (weak apply).

[perryg114]

Try backing off on the adjuster. Sometimes adjusting them by the book is too tight and they won't shut off. In the worse case the heat can cause the rear seal to blow and the grease on the drum will cause the brakes to lock.

Perry

[Al and Missy]

Just to be clear, the action of the brake on that one wheel is binary. It is either on or off. When pressing the brake pedal, at some point that brake, and only that brake, locks up. when I release the pedal, all brakes, including the locked one, release.

When I serviced the bearings, I took this brake assembly (and all others) apart, and cleaned and lubricated them per the Dexter brake service manual.

Al

[TG Twinkie]

The brake shoes may not be adjusted close enough after the miles you drove. If they are out of adjustment too far. They could "cam over" and lock up. If either shoe is not making full contact with the drum when applied. They could grab. I would check the wear pattern on the shoe.


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[J. Morgan]

Electric brakes can get grabby when they are adjusted TOO LOSE.

The brake shoe might have worn into the shape of the drum and got lose quickly.

Try adjusting the brakes to see if this might be your issue.


1/2 Ton 4WD Truck, 72 Sovereign Hensley Arrow

[Rolland]

Also make sure you didn't put the shoes on backwards, there is a front and rear on most brake setups (Front leading lining is shorter)


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[J. Morgan]

Duh... Loose...

Too late to edit... Sorry.


1/2 Ton 4WD Truck, 72 Sovereign Hensley Arrow

[perryg114]

They can also do this if adjusted too tight. The symptoms would be they never shut off and run hot. The full on or full off might be caused by the too loose issue.

Perry

[Jbart]

Right rear wheel locks when in reverse. all release when in forward. Warning light on truck instrument panel says wiring fault in trailer. Any Ideas or suggestions for a starting place to eliminate this. 1972 Sovereign 31 ft. 2014 Ford 150 4 wheel.

Thanks!

JB

[J. Morgan]

Usually when an electric brake locks up in reverse it means that a brake assy. From the left has been installed on the right or one from the right has been installed from the left.

The wiring can almost be assumed to be good providing that all four brakes work.

The wires can be checked with a test light or voltmeter.

Most all brake wiring problems are either near the pigtail or between the brake magnets and the point where the brake wires exit the trailer body bear the axles.


1/2 Ton 4WD Truck, 72 Sovereign Hensley Arrow

[J. Morgan]

By the pigtail I mean near the back side of the 7 pin plug.




1/2 Ton 4WD Truck, 72 Sovereign Hensley Arrow

[Jbart]

Thanks J. Morgan! Think you got me thinking in the right direction! JBART

[TG Twinkie]

Brakes will lock up in reverse when they are too far out of adjustment. They will cam over and lock. This can happen when moving forward as well. But it will show up in reverse first.


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[Al and Missy]

Update- I adjusted all four brakes and the left rear still grabs. We had plans to travel for the holiday (without the trailer) so we were in a bit of a time crunch. I tested the brakes on the way to storage, so i'll have to pull it early for Canopener or before to tear down that wheel and see what is going on.

Al

[Rolland]

I just spoke with a fellow the other day who had the same problem. His turned out to be the wrong part installed in the brake,the correct part number, but there is evidently a error in the book. With this part in it the brake will lock when applied, and not release. You may have to compare the parts with the brake on the other axle. Hope this is some help. Rolland


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[Al and Missy]

Thanks Rolland,

Do you know what part it was?

I started another thread to discuss the possibility of centering the backing plate on the axle as I found some info on an SOB site that indicated that could be the problem. I have since removed the drum and inspected the brake assembly without finding any problem. I did notice that this brake was dragging a little more so I backed off the adjustment. We are going to the Canopener Rally in January so it will get a checkout, and if It is still acting up maybe someone there will have an idea.

Al

[perryg114]

Dragging brakes is not uncommon. Back off the ones that are running hot till they don't run hot. Your hand will tell you which ones are running hot.

Perry