Last Winter I replaced my 10" travel trailer brakes at about 7,000 miles in preparation for an extended trip. I'm going to break up what I have learned into several items for clarity.
Brakes And Bearings by lynnmor | Photobucket
Here is an overview with approximate total trailer miles of the service, replacements and repairs:
1,000 miles the wheel bearings were repacked and new aluminum wheels were installed with LT tires. The drums, wheels and tires were balanced as a unit. One brake was not properly connected and that splice was repaired.
7,500 miles the drums, brakes and bearings were replaced and assemblies were balanced.
18,000 miles the drums and armatures were turned and the defective wheel bearings were replaced.
See below what I found and why I replaced the various components. Note that I am discussing #84 spindles and 3,500 lb. axles that are used on many, and possibly most, travel trailers.
At 1,000 miles, I found the original Al-Ko drums to be out of balance by as much as 5.5 oz. I compensated for that by installing the heavy spot of the wheel opposite the heavy spot of the drum, and then balanced the assemblies.
At 7,500 miles the drum armatures were grooved and galled so deep that I would have had to remove twice as much metal that is allowed to true them. I'll add more about that later. The Al-Ko drums were replaced with Dexters.
The Dexter drums were cast much better and the balance was out 1 oz. or less. I should add here that neither manufacturer balances the drums.
The Dexter drums had the bearing races pre-installed and eTrailer supplied the bearings.
At 18,000 miles, the Dexter drums were turned and about half of the allowable amount was removed from the armatures to true them.
When I saw the deep grooves in the Al-Ko armatures it became apparent that the magnet design was part of the problem. Note the unbroken line of steel at the bottom edge of the magnet. That area didn't wear down with the rest of the magnet and it cut into the armature face. Compare the larger Dexter magnet to the Al-Ko magnet and you will see why I switched brands.
Here is my theory why there is excessive magnet and armature wear:
You might have read that new brakes are very weak and need to be burnished by doing numerous hard stops. Most likely a driver would increase the controller setting possibly up to its maximum to get any reasonable amount of braking. Now remember that even though braking is weak, the magnet is attracted to the armature with maximum force. Now here you have two new surfaces, ( the magnet and the armature) that have not yet mated properly. The result is galling and the beginning of wear that will feed on itself.
This time around, I will forgo the burnishing operation and even turn down the controller for a while. Yes, that is not a great idea from a safety standpoint.
When I bought the new Dexter drums they had the bearing races pre-installed. I used the cheap Chinese bearings that eTrailer shipped with the drums. That turned out to be a mistake as I discovered during the inspection at 18,000 miles. The poor quality of the steel, the poor finish and even a ridge left from a faulty grinding operation caused the bearings shed metal and were on the verge of major failure.
Note that some rollers were failing while others were not. I used Valvoline grease.
I replaced all bearings and races with USA made Timken. This time I used Timken grease.
There is a design flaw in the #84 spindle. The spindle shoulder, where the inner bearing contacts, is only .028" wide by design. With manufacturing tolerances, this could be as little as zero.
I found excess bearing clearance in one spindle. Upon inspection, I found the bearing had worn into the tiny shoulder mentioned above. The shoulder contact area was only .021" wide.
There is no easy fix for this problem. The bearings have a .14" radius that is not ground. If that extremely small contact area wears away, the bearing will be loose and not run true. The seal diameter should have been designed larger.