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Open Roads Forum  >  Tech Issues

 > One brake over adjusted

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Gdetrailer

PA

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Posted: 06/24/22 09:42am Link  |  Quote  |  Print  |  Notify Moderator

Brake shoe could have gotten stuck and not releasing, possibility?

Sure, anything is possible.

With only 1500 miles on the rig it rules out brake parts being rusty, everything should still look like new.

Monitor things for now until you are satisfied everything is correct and good then move on if no issue is noticed after a another trip..

enahs

Washington

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Posted: 06/25/22 07:19pm Link  |  Quote  |  Print  |  Notify Moderator

Ran across something coincidentally. The arm that holds the magnet on manually adjusted brakes can, under certain circumstances, ride up on the back edge of the engaged brake shoe and then prevent the shoe from fully disengaging. One thing that can cause this is a worn or ill fitting bushing on that arm allowing excessive side play. I don't know that that is what happened here or why it should happen on new brakes. But it can be a cause of a hanging brake. And it is something to check for when doing a brake inspection.


'07 Chevy 3500 Dooley, CC, LT3, D/A

Matt_Colie

Southeast Michigan

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Posted: 06/26/22 09:00am Link  |  Quote  |  Print  |  Notify Moderator

Enahs,

It sounds like you have isolated the problem, now you need to fine the real cause. This can be an issue.

I used to work in quality for a Detroit first Tier. It became clear to me that unless quality programs are forced on most manufactures, they will not embrace them. The fact is, that there is very possibly a component of that brake that is the problem. It might not actually be out side of the manufacture's tolerances, but those tolerances may be quite worthless. Finding the problem part can also be a big problem. There is also no reason it has to be just one part.

Matt


Matt & Mary Colie
A sailor, his bride and their black dogs (one dear dog is waiting for us at the bridge) going to see some dry places that have Geocaches in a coach made the year we married.


JBarca

Radnor, Ohio, USA

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Posted: 06/26/22 05:10pm Link  |  Quote  |  Print  |  Notify Moderator

enahs wrote:

I appreciate all of the potential scenarios. But none are consistent with the shop's alleged findings. All brakes are fine. No excessive wear. The offending brake was supposedly much over adjusted. But none of this showed up for 1500 miles. Now, just prior to the smoking event, there had been a lot of rain. And the trailer then sat for several days before heading home and encountering the smoking issue. I am wondering if this is a matter of a brake failing to release, a bit but not much over adjusted. In any case, in a few days we will give it a good test. If the problem reappears, all new components will be installed — brakes, bearings, drums. BTW, Dexter now does not plug the brake adjusting ports in the backing plates, There are two of them in each plate and they are left open. We've since properly plugged them.


Hi,

Just found your post. As a point of view from my background, I was one of the first here on RV net to report on installing self adjusting brakes upgrades from standard adjust. I had one wheel over adjust due to excessive drum runout. Dexter declares (or at least did then) 0.015" TIR is the spec for their drums max limit. My old Alko drum that worked on standard adjust was at 0.028" TIR and it allowed the brake to adjust into that excess clearance then then heat up badly. If you want to read more on this, see here I did a post on it in 2009 https://www.rv.net/forum/index.cfm/fusea........hread/tid/23458294/srt/pa/pging/1/page/1

I also had a similar problem with my son's trailer that he bought used with standard adjust brakes. This would be like yours, just in his case it was on 5,200# axles so a 12 x 2" brake. Not sure what yours is, but the end result may not matter.

We did the brake adjustment ourselves on his camper after we inspected and greased the bearings. Jack up the camper, spin the wheel, tweak the adjuster to get the feel "you" want then make all 4 the same feel. We also do a drag test on gravel to make sure all 4 come close to lockup at the same time. This is about 6 months after he got it and maybe only ~ 500 - 1,000 miles on the camper after the adjust.

He went camping and started complaining he had a hot front left wheel. He could smell it. And the IR gun confirmed it, it's excessively hot. After the system cooled down, it was not as bad but the brake was grabby. We backed off 5 clicks and tried again. In a short while the same thing happened. A hot wheel, backed off another 5 clicks, same thing. And I know which way back off is.

After we backed off 20 plus clicks, OK something is messed up how this brake keeps getting so hot. Jack up the camper, with 20 plus clicks backed off, the wheel spins free as can be. This is a brake engagement issue.

Tried several checks and parts changes to back into what was the issue? Started with an amp check on the magnet coil in case it was pulling more power for some reason, nope. It was not the coil, we even changed the coil. No change, the wheel would still go into mega heat after only a few stops. And it needed stopping to get hot.

Changed the magnet arm with an older spare I had, thinking it would jam for some reason, nope no change.

Next we changed the entire brake plate, I had 4 Alko half used complete plates with shoes, magnets and adjusters left over from my self adjust upgrade. It changed nothing, the newly changed brake still would get hot. OK there is only one part left, the brake drum.

I have a 5,200# axle stub I can do a brake drum run out bench tests on. I first checked the diameter of the brake shoe surface, it measured 12.001" to 12.003"ID. OK, the shoe surface is round enough, but what about the run out to the bearings? Used the bearings from the camper in the drum and indicated it. The shoe surface is 0.025" TIR plus spinning out of round with the bearings.

I am from a machine shop background and have a pet peeve with the trailer industry on why they cannot machine a brake drum to spin at least within 0.005" TIR all day long. It's all in the setup of the machine.

Since my son was going to do a suspension bushing and shackle upgrade to bronze bushings and wet bolts, he bought all new brake drums and self adjusting brake plates. We indicated each new brake drum before putting them on. 2 of them were less then 0.005" TIR, the other 2 were less then 0.008" TIR so we put them on. The problem went away.

This is what I came to conclude from this standard adjust self brake up issue.

1. The brake drum was too far spinning out of round.
2. We manually adjusted the brakes to a slight drag feel with the wheel off the ground. It is common to have a drag spot and a skip no drag on trailer wheels as felt during this process. The drums runs out of round but you never know how much.
3. All 4 brakes where set to be the "most" efficient, not a lot of lost motion/play in the system.
4. When the problem brake engaged, the magnet arm moved the shoes into the gross run out area of the drum. As the wheel then turns to the tighter part of the drum, increased pressure is seen to create slip on the magnet. This magnet arm pressure creates more shoe pressure which creates more braking friction.
5.This wheel now starts getting hotter as it is doing more stopping then the other 3 brakes.
6. As the brake shoes start heating up, they can swell some, no idea how much but they can be closer to the drum with the heat expansion and the brake drum ID is getting smaller from the high heat expansion also. This make this issue even worse.
7. The heat keeps building and then the wheel can lock up partly when trying to stop. You can hear the tire skid.
8. As the system cools down and the brake disengages, the wheel spins free making this hard to figure out the issue.

Bottom line, an excessive run out on the brake drum shoe surface created this issue.

I suspect how the prior owner never found this, they never had the brakes adjusted very well or at all in it's prior life of 10 years. With the brakes very loose in adjustment, this issue may not have come to be found. It was only when we went in and adjusted them to where they were supposed to be did the issue flair up.

If you trust your shop did the right adjusting, I'm sure they may not have checked the run out of the brake drum. You have to have a bench setup with a spindle to do this off the camper, or take the entire brake plate off to get the indicator in to check the run out.

I'm not saying this is your issue, but it at least can explain how it can happen with what you told us.

Hope this helps.

John

* This post was last edited 06/27/22 12:27pm by JBarca *   View edit history


John & Cindy

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Fisherman

Angus, Ontario, Canada

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Posted: 06/26/22 07:42pm Link  |  Quote  |  Print  |  Notify Moderator

That is an interesting and very informative write up John, thanks.

JBarca

Radnor, Ohio, USA

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Posted: 06/27/22 12:39pm Link  |  Quote  |  Print  |  Notify Moderator

Fisherman wrote:

That is an interesting and very informative write up John, thanks.


Thanks, yes the learning is continuous. If one thinks they have it all figured out, then reality sets in and sets you straight, you don't know it "all". You do enough work on mechanical systems, stuff just happens!

When I had my drum run out issue on the self adjusting brakes, Dexter tech service tried to help, but back in 2009 they had not known (at at least that tech didn't) of what an excessive runout issue can cause. Here I was using that same camper on standard adjust since 2003 and the issue never reared it's head, that is until I installed the self adjusters.

I was not shocked that standard adjust brakes could have the same problem, but I at least had a heads up it might. Then we proved it when the drum gets bad enough, and the conditions are right, it can happen on standard adjust, but from a different source. While the standard adjust brake setup did not over adjust it self, gross run out of he drum can create a similar heat issue.

Thanks

John

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