Scored Brake Drum OK?

manyman297

I’ve been doing my annual service on my brakes and bearings and noticed the left side drum has some slight scoring on the brake surface. The right appears nearly perfect. 

I’ve been trying to diagnose an issue where my left brake doesn’t seem to be doing nearly the same work as my right drum (right drum is always much hotter). I’ve already adjusted the starwheels and all of that and have done extensive electrical testing on the magnets. Everything checks out.

 

The scoring is slight…can’t even really feel it as I drag a fingernail over it except one small groove.

What do you think? (Pics below)

[Deleted User]

I don't know much about brakes but I do know this indicates your brake pads are worn out on a car and its cutting into your rotor...bad thing. Does the T@b have same kind of brakes? I don't know. 

manyman297

So the linings look fine. A good 1/4”+ maybe on them. I’m tempted to put it all back together and test drive it but I also would hate to have to repack the bearings if I did need to get it resurfaced. 

Grumpy_G

Don't forget that electric trailer brakes have *two* friction surfaces, besides inside the drum where the actual brake shoes touch there's also the area where the magnet rides. The magnets tend to have more friction variance than brake shoes. I only had one trailer where braking was pretty even. 

As long as the trailer can noticeably slow down the truck when applying the trailer brakes you should be good. 

manyman297

@Grumpy_G

the magnet surfaces all look fine. It’s just that light scoring on the lining surface that looked different between the two drums.

Before servicing the brakes I did a test drive both on highway and city. Highway was fine. Both drums had a low, even temp. City was where the differences were sometimes extreme. At some points the right drum was reading 40+ degrees hotter than the left drum. 

Grumpy_G

What I was trying to convey is that regardless of how the magnets and the surface in the drum looks like there are variances. The magnets are made from the finest chinesium, plus the magnets are typically wired with one being closer to the plug than the other (more voltage drop) so I wouldn't be surprised if there is a 10% difference in magnetic field from side to side.

manyman297

No voltage drop from side to side. Nucamp used 14awg wire between the two magnets which provides plenty of flow. 

The right side brakes are just getting way too hot compared to the left side. I can understand a 10 degree difference but 40-50 degrees tells me something isn’t right. Planning to put it all together and test drive it tomorrow so we’ll see. Maybe I had some grease or surface contaminant. 

tabiphile

I'd be inclined to carefully clean everything, give the rough one a sand with some medium grit silicon carbide paper and reassemble. They don't look that bad. Having said that, it would be nice to see what the pads look like. 

Mickerly

   The brake shoe surface looks like you have almost new shoes.
   The surface in question is where the 'magnet' rides. This looks like normal scoring. A utility trailer repair place may be able to clean up the surface to make it look new. I would only do that if I were replacing the magnets too. Their surfaces need to match.
   The difference in temperature tells me that one brake is adjusted a touch too tight, very lightly rubbing. That small of a temperature difference is probably an adjustment issue. I would clean everything with spray brake cleaner keep on going. Listen very closely as you turn the wheel. Tighten until it just starts to touch then back off 2 clicks. Make sure you make a complete rotation of the wheel between adjustments. I don't think there are round brake drums any more.
   Many brake controllers understand backing. If one didn't, the scoring from the magnet is worse when backing. I disable my trailer brakes when backing to avoid the problem. Then again, I'm old and this is not necessary with several of the newer brake controllers.
Have fun...

manyman297

@Mickerly

Great info. Thanks!

So here’s my adjustment anomaly. Left doesn’t seem to be doing the job the right is doing (heat difference). I adjust the left to almost being too tight…still the right drum is hotter. Back off the right A LOT…still the right brake is hotter. That’s what lead me to tear apart the wiring and do some multimeter testing. Everything checks out.

And with regards to the scoring. The area I was concerned about was where the linings contact the drum. You can see on the one photo where there are light scoring lines. The magnet contact surfaces look fine.

manyman297

Just wrapped up putting everything back together and drove around the city for an hour and a half  :(

I usually have my tekonsha p3 set to 3.5 which is admittedly a little weak. Right off the bat that setting felt like it was doing nothing. Set the controller 8.5 and was getting good braking so I continued driving. Got out and checked temps with an infrared gun. Temps were much closer to each other. At one point they were exactly the same. 

As I drove the braking got better so I backed off the controller until I was back at 3.5. I sprayed the linings with brake cleaner so maybe it had to wear in a bit.

The biggest swing I recorded was 25 degrees difference. Previously I was getting 40-50 degree differences.

I’m going to keep my eyes on this issue over the season. Maybe I had some grease contamination or something. Things seem better now. 

Mickerly

The light ware I see on the photo looks like normal use. Both drums should look about the same. 

It's all about the adjustment. You may notice, as you adjust tighter, the brake will drag in one wheel position. The problem is a combination of slightly out of round drum and shoes not arced for the drum. That's why I get a full wheel rotation with each click. When that one spot doesn't touch, I get one more click loose.

If you are worried about the electrical side, use a volt meter to measure the voltage at each 'magnet' when the brake is applied. These trailers don't go under water, so corrosion typically isn't the issue. If the voltage is balanced, there are only two other factors: friction and adjustment. A very small touch of white grease where the side of the shoe touches the backing plate will significantly reduce friction. I had to do this on one of mine to get them to act equally. Most of the time adjustment is the greater variable.

A personal thought, in my opinion, the Dextor parts work better than other after market parts. They are more expensive, but they work better. "Your mileage may vary." Good luck.

manyman297

@Mickerly

What you said below piqued my interest but can you clarify a bit more:

“ It's all about the adjustment. You may notice, as you adjust tighter, the brake will drag in one wheel position. The problem is a combination of slightly out of round drum and shoes not arced for the drum. That's why I get a full wheel rotation with each click. When that one spot doesn't touch, I get one more click loose.”

I feel like this may be the issue. I did notice the leading lining on the driver side (the least hot side originally) had what looked like wear only on the center of the lining…maybe a symptom of out-of-round linings and possibly reduced braking capacity and less heat buildup. 

I feel like this may be the issue. I did notice the leading lining on the driver side (the least hot side originally) had what looked like wear only on the center of the lining…maybe a symptom of out-of-round linings and possibly reduced braking capacity and less heat buildup. 

I did grease any contact points with the backing plate. As I mentioned they seem to be working better but still not quite there.