Trailer Brakes Weakening

[Dr.Lightning]

So I have this feeling that my trailer brakes aren't as strong 12 months after I first bought this used Heartland Pioneer, at which time I had the brakes checked by my own mechanic. I could be mistaken about this feeling. They never locked up on asphalt, but I have this feeling for the jerk behind me when I manually engage the trailer brakes only, and I have a feeling that this jerk isn't the same. All trailer brake settings are unchanged.

I went through a whole bunch of checking using an oscilloscope, looking at the the brake signal and the drop across the ground reference at various places (battery, 7-pin trailer plug, travel trailer junction box, wire junctions right at the front right wheel of two axles). Note that I have a PhD in Electrical Engineering and I have done race car data acquisition electronics hardware/software/firmware design for 30 years. So I really should know what I'm doing, unless I'm going insane.

SANITY CHECK: I have a 2015 RAM 1500 with oem brake controller. This thing produces a maximum 75% duty cycle square wave for braking. The peak-to-peak magnitude of that signal is 15.6 volts measured right at the wire junctions next to the front right trailer wheel (two axles). Ignoring the 0.2V excess, this is the exact same peak-to-peak magnitude of 15.4 volts that I measure everywhere else. So while there is a variation in ground of as much as 2.2V, that REALLY DOES NOT MATTER if the two wires right at the wheel are measuring 15.6V. THIS IS MY ONLY SANITY CHECK QUESTION RIGHT NOW, NOTHING ELSE. So, am I correct that as long as the peak-to-peak magnitude of the square wave right at the wheel is 15.6V, then nothing else matters relative to sufficient or insufficient ground wires or brake power wires. Right?

See, if the above is true, then there simply cannot be anything wrong with my wiring or brake controller. 15.6V right at the brakes themselves (at least a few inches away at the wire junctions next to the wheel), means that the brakes are getting the full voltage range possible. Only secondary questions remain, like why did I measure 15.6V p-p at the brake, while all other measurements were 15.4V p-p, with different ground references while signal was at the TT junction box (resolved below). I call this "secondary" because 15.6V or 15.4V, Tomato/Tomaato, shouldn't make any difference. Also, why does the brake controller never issue more than a 75% duty cycle? That's just what this 2015 RAM 1500 oem brake controller does. Furthermore, changing the setting from "Light Electric" to "Heavy Electric" actually goes the opposite way from expected on many forums I visited -- the duty cycle goes down to 61%, thus providing even less net braking. (It seems "Heavy" doesn't mean, "I got me a heavier trailer so I need more braking power". Instead perhaps it means, "the brakes themselves are stronger and so I don't need as much braking signal to get the braking I need.")

So, I ask once more. Within the constraint that the oem brake controller won't send out more than a 75% duty cycle signal, as long as I have full voltage right there at the two wires going into the brakes, then the signal going in to the brakes is the best it's going to ever be with this controller.

Finally about this "15.6V" thing. At the same time as the signal going to the brakes themselves is 15.6V p-p, the battery is at 14.5V. Meanwhile, the negative excursion of the square wave is between -1.62V and -2.2V, depending on which point I'm using as a ground reference. So at this point it's obvious to me that this 2015 RAM 1500 oem controller has a negative power supply inside of it that's generating at least an extra -1V on the ground side, if not -2V. Perhaps it does this to compensate for anticipated poor trailer brake wiring, perhaps poor trailer brake ground wiring. So this darned negative voltage I'm seeing is perhaps not due at all to voltage drop in my wiring, but because the controller is generating it on purpose. In addition, on my last check, with ground vs signal both measured at the truck connector, that 15.4V p-p was actually fluttering a little on the scope numerical analysis result, between 15.4V and 15.6V. So simple fluttering of this value answers the 15.4V vs 15.6V question. Maybe it is actually very close to 15.5V, but the numerical analysis display rounds to 0.2V and thus flutters between 15.4V and 15.6V as the 15.5V varies ever so slightly. I've known this effect extremely well since I think 1992, including watching it on live video behind the astronauts on the space shuttle (or station) way back then. So I don't think that's in fact any measurement difference at all. This leaves me with my original question. If I'm seeing 15+ V right at the brakes, then I do NOT have a brake wiring issue, in the trailer or the truck, that needs to be fixed. Right? Or am I going insane?

 

[Gary521]

Perhaps it has nothing to do with voltage to the brakes but the brakes themselves. Are they self adjusting brakes or manual adjusting brakes? Maybe they need adjusting. Electric brakes probably will not lock up anyway. Perhaps the connection point is not making good contact? Maybe there is grease on the shoes? Maybe your mechanic is not familiar with electric trailer brakes? Maybe??

 

[Bob.jr]

Probably just need a brake adjustment.
How are you getting 15 plus volts, when your alternator is putting out 14.3 volts?

Sent from my SM-G781U using Tapatalk

 

[Dr.Lightning]

Thanks Gary & Bob. You've both pointed directly at the brakes rather than the wiring, which is where I was getting as well.

The fact that the brake signal is going well below auto ground was what got me hunting down ground lines first. But now I'm convinced that the controller has a negative power supply in it. That, of course, is how the p-p voltage exceeds the battery/alternator, Bob. Who knows, that controller might also be bumping the positive supply up higher than the incoming auto voltage as well. I *know* it's doing something. (FYI, I've designed many DC-DC converter circuits in my day that take something like 5V in to produce as well -5V and +12V out. So this is a very common thing in electronics.)

I have decades of electrical experience, a fair amount of auto experience, but zero electric brake experience. That's why I was checking the things I know well first. My mechanic has lots of electric trailer brake experience.

I don't know how to check the brakes themselves, don't want to fool with jacking and removing a tire and drum, and don't know if an adjustment is possible from the outside. I'm better at electronics than anyone and will do that myself. I'll pay others and take a walk in the park instead when it comes to the more physically demanding or the things I don't know.

So, indeed, *now* it's time to take the whole rig to my mechanic for him to double check the brakes. The truck needs an oil change too! Unless somebody can tell me a trivial way I can adjust the brakes from the outside... Of course, an experience eye checking the inside of the brakes is a time that has come again, anyway.

Thanks very much.

P.S. the 12V main voltage wires were all rusted inside a huge blue nut, with no dielectric grease. I've cut those wires back to clean strands and replaced that connector with a nice lever nut from Amazon (here) along with grease and black electrical tape to keep it from leaking out. Also, OMG, inside the TT tongue junction box I discovered that the breakaway safety break wire was cut off from the brake wires -- so there was no runaway protection from the day I bought the trailer. Don't know what irresponsible person did this, hiding the fact inside the junction box. But I put on a new Curt breakaway switch (here) and tested it while I still had my scope attached. Full time power when the plug was yanked out of the switch. Finally, I'm about to add Gorilla tape over the top of the junction box like a bit of an attached roof in order to reduce the moisture going inside -- I think trying to totally eliminate all moisture is a fool's errand. All in all, the time spent diagnosing the trailer brake electrical was worth these two side items., especially the breakaway safety switch!

 

[Dahillbilly]

if the brake shoes were not burnished correctly when new OR overheated at some point they will not brake as effectively. I'd see if they are self-adjusting shoes and/or have your mechanic adjust them

 

[Dr.Lightning]

if the brake shoes were not burnished correctly when new OR overheated at some point they will not brake as effectively. I'd see if they are self-adjusting shoes and/or have your mechanic adjust them

Perhaps it has nothing to do with voltage to the brakes but the brakes themselves. Are they self adjusting brakes or manual adjusting brakes? Maybe they need adjusting. Electric brakes probably will not lock up anyway. Perhaps the connection point is not making good contact? Maybe there is grease on the shoes? Maybe your mechanic is not familiar with electric trailer brakes? Maybe??

Probably just need a brake adjustment.
How are you getting 15 plus volts, when your alternator is putting out 14.3 volts?

Sent from my SM-G781U using Tapatalk

So I figured the bearings needed repacking after a year, and so I took it to the mechanic anyway. The bearings were redone about a year ago (I paid on 3/3/22). Today, I look and my Everlance mileage logger tells me we've driven 9,330 miles since that date. Well, indeed my 10K miles or 1yr time for bearings was about right in both regards.

There was lots of grease inside the drum and the pads were overheated and worn most of the way down. I suspect that the grease leak occurred first, and then I had to turn up the brake controller gain which helped wear down and overheat the brakes.

Meanwhile, NOT automatically adjusting brakes.

Now my question is WHY was there so much grease inside the drum? I would have thought that the bearings were at least somewhat sealed. The axle is from DEXTER and I think part number 0121436. Or maybe it's 3228660. Too many numbers with insufficient identification! Below is a photo of the label on the rear of two axles on this Heartland Pioneer RK280. Is it possible that when the bearings were serviced a year ago, something wasn't done properly? I don't have a photo inside the drum. (EDIT: The video here says in the beginning "standard bearings" and later mentions a "seal". So this makes me wonder if it was done wrong before. Or do they just sometimes fail? Why else would Gary521 ask about grease?)

Thanks!

 

[rhodies1]

2 reasons.. grease seals failed or too much grease was inserted through the grease zerk and this can cause the seal to blow out

 

[david-steph2018]

So I figured the bearings needed repacking after a year, and so I took it to the mechanic anyway. The bearings were redone about a year ago (I paid on 3/3/22). Today, I look and my Everlance mileage logger tells me we've driven 9,330 miles since that date. Well, indeed my 10K miles or 1yr time for bearings was about right in both regards.

There was lots of grease inside the drum and the pads were overheated and worn most of the way down. I suspect that the grease leak occurred first, and then I had to turn up the brake controller gain which helped wear down and overheat the brakes.

Meanwhile, NOT automatically adjusting brakes.

Now my question is WHY was there so much grease inside the drum? I would have thought that the bearings were at least somewhat sealed. The axle is from DEXTER and I think part number 0121436. Or maybe it's 3228660. Too many numbers with insufficient identification! Below is a photo of the label on the rear of two axles on this Heartland Pioneer RK280. Is it possible that when the bearings were serviced a year ago, something wasn't done properly? I don't have a photo inside the drum. (EDIT: The video here says in the beginning "standard bearings" and later mentions a "seal". So this makes me wonder if it was done wrong before. Or do they just sometimes fail? Why else would Gary521 ask about grease?)

Thanks!


View attachment 68368

With grease inside the drum, the rear or front seals are bad. You will never get all the grease out; it would be better to get new drums. If you do, make sure you get the correct wheel assemblies.

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