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Old 10-19-2014, 09:06 PM   #1
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1970 23' Safari
Oshawa , Ontario
Join Date: Jul 2014
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HELP - Electric Brake Problems

I have a 1970 Airstream, single axle. I just put new loaded backing plate assemblies on. The drums looked good so I installed new bearings and put everything back together.

As I was adjusting the brakes today I noticed on the lefthand side that the wheel would grab a bit when turning it backwards, sometimes to the point of jamming. Forward, no problem.

I had to move the trailer 250km today, so I hooked everything up and made the trip. The brakes got progressively better throughout the trip as they bedded in, and I was able to get the controller set for nice smooth braking. I was really happy.

So when I got home I had to back into my long, narrow driveway. As soon as I started reversing the left side wheel started to lock up (even without touching the brakes). I disconnected the wiring for good measure and it didn't matter. So it would lock up pretty good in reverse, but release if I pulled the trailer forward.

Somehow I got it into the driveway. I jacked it up, took the drum off, and everything seems normal inside. I don't see anything that could be causing it to jam. I adjusted again and tried to find the problem, but no luck. With the shoes adjusted tight and backed off slightly the wheel turns forward no problem. Turn the wheel backwards a few full revolutions and boom - locked up tighter than a drum!

This is a correct left-side backing plate, magnet and leading shoe installed as per all the images I can find online, exactly as it came out of the box.

Tomorrow I'm going to take it apart again in the daylight and see what I can find. I'm wondering if there is any rust left in the drum that catches the shoe and causes it to bind...

So, what's going on? Any ideas?

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Old 10-20-2014, 08:52 AM   #2
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1966 26' Overlander
Phoenix , Arizona
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Any rust on the braking surface would have been taken off by several applications of the brake shoes in a forward motion.

On a car or light truck this can happen with the primary and secondary shoes mounted in reverse. However you state otherwise in your posting.

The other thing to look at is the chamfer on the leading and trailing edge of the shoe. There should be some versus a 90 degree angle of shoe material at each end of the shoe. Lastly would be the arch of the shoe is not fitted to the drum. (In correct shoe or incorrect lining/lining cut or trim) The ends of the shoe are contacting the drum and not the center. There would be wear marks on shoes ot show this.


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Old 10-21-2014, 05:56 AM   #3
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1970 23' Safari
Oshawa , Ontario
Join Date: Jul 2014
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Thanks for the reply. I've checked for the leading / trailing shoes, chamfer on the shoes, etc., and everything is OK.

But, last night I found the culprit. I decided to temporarily take the spring off the magnet and push it backwards against the backing plate to make sure it wasn't causing the problem. With the drum back on and brakes adjusted the problem was gone....

So I think the magnet is catching or dragging on the armature, which is not perfectly smooth, and causing brake application in reverse. If it ever stops raining here I will take it apart again and have the armature smoothed out and that should solve the issue...
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