Breakaway switch not working... and maybe brake issues

[Bill]

Originally Posted by rickst29

Delighted, even. I had imagined the cycle time for a brake controller to be > 100 kHz, causing the meter to respond to the average (rather than the peaks). More like a solar controller in PWM mode.

Rickst -

Actually, there is some truth in your observation. An old-fashioned VOM has a mechanical meter, and a mechanical device has some inertia. This in turn means that on a DC scale, it will respond in some way to the average value of the input. Since old-fashioned VOMs are fairly rare these days, without even thinking I was describing electronic meters, which have no inertia. What many of them do is read the peak value of the input (presumed to be a sine wave if you put the meter on an AC VOLTS scale), multiply by 0.707, and display the result. They do this because the RMS value of a sine wave (think of RMS as a different kind of average) is 0.707 times the peak value, and the peak value is easier to measure. By contrast, if you put the meter on a DC VOLTS scale, the meter simply grabs the peak value and displays it, under the assumption that the input is DC.

Different meters have different ways of handling all this, which is why I began my post with "Beware", rather than "Wrong!".

Bill

[Splash]

SOME ANSWERS...

First, thank you all! , even the pulse stuff is interesting and helpful (yes, I could follow! Maybe not exactly 100% but I got it and it may explain some things).

So...

Larryjb, what you mention above was the major problem. Either the right side/left side brakes were never connected, or somehow they were cut (how?! ) . Based on the wiring diagrams, I restored the side to side brake connections and now the brakes clearly all engage. Yay! I shudder to think that I've been using only one side of the brakes for who knows how long (up to 20 years!) but at least it is a fairly light trailer. Except for the first 3 years, I've had a big truck and I suspect the truck braking overtook the trailer brakes.

LARRYJB- if you care to elaborate, I'd love to know how you determined that the magnet was badly worn. Did you tear down the breaks? Test magnetic strength somehow? My situation seems similar and the magnet could be worn... did you replace the magnet or get all new brakes? . Maybe I should just get new brakes all around but my curiosity is itching to learn something new.

ALSO, RE BREAKAWAY: when I fixed that side-side problem, it fixed the emergency brake away failure issue. I'm not sure why but I have a couple theories:

1) maybe one side of the brakes *was* engaging (when breakaway pulled) even before all this fixing and maybe it just wasn't strong enough to be noticed. Could this be evidence of this pulse thing? Maybe not getting full voltage sometimes? I have a cheapo voltmeter... and a little knowledge can be dangerous. It's probably not wise of me to think that I could fix more with a better multi meter (great excuse for another gadget... but should I?)


2) perhaps those pigtails that were flying free were shorting intermittently and causing the trailer disconnect and failed breakaway. Hmmm... maybe.that seems a stretch. The pigtails aren't very long, in resting state the live ends are a couple inches from the axle .

RESULT: the brakes and breakaway now work - testing wheel roll while the trailer was up on jacks showed immediate locking.

COUPLE LAST QUESTIONS for those of you still reading. On jacks, the wheels lock up tight to hand pushing (just like the brake instructions say to do) ; when testing with the truck, the brakes can be heard and "felt " but I can see that the wheels still roll some after breakaway is pulled - tight resistance but still some roll. Is that just poor brake pads at this point? Is it supposed to roll a little so that the tires don't get braking wear spots (kinda like ABS but I think this was PRE-ABS)?

Thanks again! Soooooo helpful

[Bill]

Originally Posted by Splash

On jacks, the wheels lock up tight to hand pushing (just like the brake instructions say to do) ; when testing with the truck, the brakes can be heard and "felt " but I can see that the wheels still roll some after breakaway is pulled - tight resistance but still some roll

Sadly, this an old and annoying issue. Instructions always say "Lock the brakes", whether you are reading brake instructions, controller instructions, or whatever. The fact of the matter is that to my knowledge, no one has ever been able to lock the TM brakes on dry pavement. Add some sand, and yes, it can be done. But not on dry hard pavement. Apparently the weight of a TM, and the grippiness of rubber tires on pavement, is sufficient to overcome the braking force that would lead to locking. Bottom line - tight resistance will slow the TM down in the event of a breakaway.

Bill

[Larryjb]

Splash,

With the funny stuff going on with the brakes, I just bit the bullet and replaced the entire brake system. New brakes, bearings, etc. It wasn't all that expensive, and I knew everything was good. It also saved a ton of diagnostic time.

Once I pulled things apart I discovered that the magnet on one side was wearing which explained an intermittent "no brakes" warning on my contoller. A cut wire explained why my trailer seemed to fishtail at other times when applying the brakes. I had only one brake working intermittently.

The thing with the magnets is that you have to pull the drum to inspect the condition of the magnets. They may be working for now, but they could be worn to the point when you may have trouble on your next trip. Once you've got the drum off to inspect the magnet, you're half way to installing new brakes anyway because you'd want to repack the wheel bearings at the very least. But, if you don't know the condition of the wheel bearings, you'd want to replace them anyway.

[Splash]

Originally Posted by Bill

Sadly, this an old and annoying issue...The fact of the matter is that to my knowledge, no one has ever been able to lock the TM brakes on dry pavement...

Bill

Thank you, 1000 times thank you - I'm taking this with me! I've been dealing with VIN issues and...long story short... I tried to get a Colorado VIN inspection last week but couldn't because of the failed emergency breakaway. What he said, however, was "See? your tires are rolling, your brake isn't working! Failed inspection.". Now I've fixed everything, the brakes are definitely gripping MUCH better, but it still rolls a bit, and I'm worried that they'll say something similar next week when I try again. At least I can tell them a (truthful) "it's a known issue".

(I've posted about the VIN issue on the forum - I was waiting to get it all fixed before I post a recap - what a nightmare!)

[Splash]

Thanks, Larryjb. I looked over the brakes and it didn't seem like there was a simple magnet check so I was curious. I'm not keen on taking apart trailer brakes (disc brakes, easy! These? not so much) so I think I'll leave that to the repair folks.

[Bill]

The nice thing about TM brakes is you can buy a ready-made brake assembly, self-adjusting, with shoes and magnet, all assembled, easy to install, for a reasonable price. You just remove four nuts from studs on the back of the old assembly, remove it, set the new assembly in place, replace the nuts, and you are done. Well, not really - reconnecting the wires is the hardest part. But as far as replacing shoes, magnet, actuators, springs, levers ... in my opinion the time and effort to worry about them individually isn't worth it. I think I paid about $100 for each kit (one per side) when I did mine a few years ago. The price has gone up a bit, so you will have to decide for yourself.

Now of course if the drum or the rotor face is badly scored, you'll have to take care of that, no matter what else you do. But the core of things is really easy.

Bill

[Larryjb]

And trailer drum brakes are not nearly as complicated as car drum brakes. These are about the same difficulty as disk brakes.

[Pater C]

I am glad that you found my post helpful. It seems like ages since I worked on my breaks. I do remember having trouble with the breakaway switch after my brakes were changed. In the end, the problem with my breakaway seemed to be that the line that went between the driver and passenger brakes had a problem. It was not sending any voltages to the passenger side. I didn't bother trying to test the wire, I just replaced it and then everything worked.

Bill has suggested many times purchases a Digital Voltage meter which has a loop that measures DC voltage (most only do ac). I called my future brother-in-law who had one and we diagnosed the problems much more quickly than trying to pierce the wire insulation with probes or playing twister to connect various points instead of us just using the loop. With my brother in law and the loop, we narrowed down the problems very quickly.