Electric trailer brakes uneven drag around rotation

[chilly81]

I'm replacing the brakes with brand new dexter assemblies, hubs, bearings right now.

I put the new ones on and I'm getting uneven drag on a couple of them. Like I can spin it and it will rotat through 270degrees of rotation then the drag will stop it and I have to turn it through the last 90 degrees by hand. It's not like it's hard to turn, but it's definitely dragging the brakes more significantly during that portion.

I can't envision a scenario where this has anything to do with my spindles or the backing plate. It really has to be the runout of the drums or possible the bearing races - as those are the only moving/rotation components.

Anyway - is this normal or acceptable to some degree? Kind of bummed these are brand new parts and I'm a bit worried.

btw, these are self adjusting and I haven't yet applied or adjusted them - but they are obviously close and dragging some at some point during rotation.

Thanks.

[Lynnmor]

It took me 1000 miles for new brakes to reach maximum effectiveness. The "bedding in" process is because of the kind of friction material used in recent years. It needs to deposit a film on the drum surfaces as well as wear to conform to the drum. What I have noticed is that the controller has to be turned up way too high to get even marginal braking. Now with the high setting the magnets, that have yet to mate to the armatures, are overworked and galling is likely.

[chilly81]

Took it out today with mixed results. On the plus side, they don't get hot if they aren't being used (which was my worry - cooking them from drag). On the down side, they really don't work that well. I need to keep bedding it - haven't been able to do too many cycles. They are working somewhat though, and all seem to heat up somewhat uniformly during bedding runs. No where near locking up yet though which saddens me somewhat.

This is a bursting-at-the-seams #7k trailer on dual #3500 axles, so I wouldn't be shocked if they can't lock up on pavement, but they dang well better lock up on dirt. (I mean with the manual trailer-only control - not in normal use). I have pretty heavy wire going back to the brakes, so don't think it's voltage drop. Will give it a little more time - they seem to be improving slowly.... only done like 10 cycles from 40mph-20mph. Have a decent ride ahead of me tomorrow, so should get some more cycles in.

[Huntindog]

Normal to some degree. Drums are much more tolerant to being out of round that a disc setup is.... That is probably why they don't bother truing them as well.

[PaulJ2]

Have worked on many and seldom find one perfectly round. I think the correct answer is- it is normal to some degree.

[time2roll]

Run them in 500 miles and give a report.

[chilly81]

Ugh. Thanks for the feedback. I will at least give them a chance to bed in tomorrow, since eTrailer tech support didn't call me back anyway. My worry is that @Lynnmor is on the right track, since mechanically, I can't see how bedding will affect an inconsistent behavior around a single rotation. It's worth a shot though, and as some have said - maybe it's not bad enough to matter and won't be as noticeable once bedded.

It sucks because I also figured out my left rear spindle is toed-in a bit and there's nothing I can do about it. I've seen far worse horror stories, but I'm looking at a new set of tires every 20k with religious rotation the way it is. That's 2 years at my current burn rate... and it tows (toes!) fine, so we'll see.

Plus, I'm full time and stuck doing repairs boondocking in the 90 deg yuma desert with 1" long horseflies (I have pics of their bodies) biting me while it's up on jackstands with me working on it.

Please excuse the venting - long day. Everyone's feedback and experiences are very much appreciated.

edit: What also sucks is that I paid a little premium to get all Dexter USA made parts and was expecting smooth sailing for it.

[Lynnmor]

No bedding will true a drum that has runout. The drums simply are not turned true to the center and it happens often. The factory tolerances are too great and is the reason that self-adjusting units can have problems. I true mine on a lathe as needed. What you have might be good enough, but I can't tell from here.

[fitznj]

Let them bed in first; your situation sounds about normal;

[RCMAN46]

As said the Chinese are not able to turn a drum true.

I even had two that were close to perfectly round but the drum brake surface was not concentric to the bearing hole.

[bobndot]

I don't really know the answer but here is a link with info on the TT brakes.



There are wear measurements (inspection portion of the link) you can look at here.

[ScottG]

Normal because the drums simply aren't round. For some reason they just can't seem to machine them round. Even new ones are that way.
So while it's not desirable, you would have to get them turned (if there's enough metal on them) to keep them from being out of round.
Mine have got around 50K on them and they have always done it.

[Old-Biscuit]

Normal......

New shoes have to be 'burnished' to seat them in

See pg 16, then pg. 12 then pg 6......Dexter Manual