I have a RV brake problem that is driving me crazy and hope one or more of our resident experts can help me. These are Dexster axles.

On my fiver, one brake out of the four is not working properly. If I jack up the wheel and have someone apply the truck brakes while spinning the wheel by hand I can hear the magnet hum and feel a very slight increase in drag, but not enough to stop the wheel turning. All remaining three wheels will immediately lock up when I do this.

Even although there was no obvious corrosion or problems I have changed all the electrical connections on that particular wheel. I measured the impedance of the magnet and it was 3.2 ohms. Just for the heck of it, I even installed a new magnet and that impedance is 3.1 ohms. Yes, the lead wires were the same color. The impedance for the adjacent wheel is 2.8 ohms and that brake is working just fine. The new magnet made no difference. With the brake drum removed and the brakes applied the magnet will barely suck a wrench against it. Voltage at the magnet is the same as the line feeding the rest of the brakes, which of course varies depending on brake pedal pressure. Did not measure amperage.

I even adjusted the shoes extra tight so that I could barely turn the wheel by hand, but it made no difference.

Any suggestions?

These brakes are relatively simple and it should not require a rocket scientist to figure out a problem, but this one is driving me bonkers.

 

swap magnets with the wheel next to it. if the problem stays you have a mechanical linkage problem but i think it will follow to the other wheel. i really hate it when i replace one bad part with another bad part.

 

Good thought. I doubt if it is a mechanical problem because when the drum is off and I move the magnet either forward or back, the shoes easily move out like they should. There is no mechanical binding either and everything is well lubricated. It just seems like the magnet does not have enough pull against the drum
Oh well, guess I had better bite the bullet and go and pull a drum on a good brake and do some comparing and/or swapping.

 

What kind of voltage to you get when the magnet is attached?

I'm wondering if one of the connections is sketchy, enough to carry voltage with no load, but that would droop off when a load is on the wire.

 

Getting 2 - 4 volts depending on brake pedal pressure. You have the same thoughts I had, which is why I replaced all the electrical connectors on that wheel. Did not do any work on it today, but tomorrow will pull the drum again as well as the the drum on the adjacent wheel (that works) and compare everything. Tomorrow will do a full voltage check at different places in the circuit as well as an amps check.

 

Swap the drum? May not have as much iron in it as the rest? Long shot...

 

That is a long shot. Along that line, tomorrow I am planning on pulling the front and rear drums and then compare how each magnet sucks a wrench against it. My bet is that the brake that is not working will have a very weak pull compared to the brake that works. If that is the case, will need to track down the reason.

 

The most common issue with electric trailer brakes is the wiring. I would vey that you have excessive voltage drop somewhere in that circuit. I recommend rewiring the circuit. Do not use ant type of slip connector. Hardwire everything, solder and heat shrink any splices or connections that you make.

 

Check the mating surface of the drum where the magnet makes contact. If it is overly scored or dirty this can effect brake performance.

 

Problem resolved!
I pulled both drums off the side that was giving me the problem. The rear brake worked fine but the front brake did not, even tho I could hear each magnet humming. Made a very 'scientific' test of feeling how hard each magnet pulled a wrench against it. Reinstalled the magnet I swapped out yesterday and it worked the same as he brake that was working. OK, so both magnets pulled a wrench with about the same degree of "pull", so what could the problem be? That pretty well eliminated an electrical problem. Hmmm, head scratching time - again.

Double checked all the mechanical parts that moved and discovered something. I had checked and lubricated everything that moved except for one tiny part. The magnet itself has to slide in and out on it's support. The magnet did slide, but was sticky and the tiny spring behind the magnet did not have enough oomf to overcome the sticky part. Figured out that even the smallest gap between the magnet and the drum would be enough to cause the magnet not to suck against the drum. Removed the magnet, sanded the magnet support and applied some anti-seize compound. That fixed the problem and the brake now works. So the problem ended up by being a mechanical problem after all.

I am a bit surprised that nobody asked how I knew one brake out of the four was not working. Even tho nobody asked, I will tell you FWIW. After my last trip I noticed that three wheels had brake dust on them, but the fourth wheel was quite clean. That made me suspicious and so I jacked up that wheel and did a brake test. The wheel still spun when the brakes were applied. Not a good sign!

Hope somebody learns something from my bumbling around this problem.

 

Problems like that can be vexing, but it often turns out to be something simple.

I'm glad you got it fixed.

 

Stan, I'm not sure who on this board is more observant about their walkabouts on their rigs you or Fiverbob! I haven't been around much lately but for some reason was thinking about you and yours yesterday at the office. I always walk away learning something form you folks and makes me wonder why I don't get on here more ... Oh yeah .. that little thing called work

Hope all is well south of south!

 

Thanks for the compliment. I am just a rookie, so the honors go to FB. He is an old f ... err geezer, so always follow his very experienced advice.

The reason I am checking everything on my RV is that I am getting it ready for my next trip on Aug 23. Just to make you drool a little bit, take a look at the link below and then click on the RV symbol at Playa Linda. My RV will be on the beach there. At the moment there is only one other RV there, so it will be nice and quiet. Not sure if we will be there for a week, a month or whatever.

http://www.ontheroadin.com/pacificco...aandzihuat.htm

 

HEY HEY, WATCH IT YOU OLD GOAT. I resemble that remark.

I was going to tell you to jack it up and put a new one under it. Buuuuuttt, that wouldn't be nice. Glad you found it - - didn't spot your post soon enough to tell you what was wrong.

GeezerBob

 

You guys and your ocean vista's make me wanna ! All we have is majestic mountains, vast golden prairies and wonderful blue skies plus a little peppering of oilsands to keep the diesels that we love going!

Enjoy!