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glenn k
1st Mar 2010, 12:44 PM
I have electric brakes on my trailer and one wheel locks up no matter how low I set the brake unit. It weighs over 3 tonne so it is a fair effort to lock it up.
I pulled the wheel off to have a look and couldn't see anything wrong lots of pad drum in good condition nothing loose. The only thing I can think of is that the flat on the back of the drum is a bit rough (as it is not smooth and shiny like the rest of the drum) and is crabbing the magnet too hard.
I was going to try and loosen the brakes up a bit but they are self adjusting so there is no point trying that: well I will leave them loose so I can get the wheel back on anyway. I have just come home to get a multimeter to see what voltage is going to the wheel. Has anyone got some suggestions? Should I grease the magnet :o
Glenn

Yonnee
1st Mar 2010, 05:06 PM
I have electric brakes on my trailer and one wheel locks up no matter how low I set the brake unit. It weighs over 3 tonne so it is a fair effort to lock it up.
I pulled the wheel off to have a look and couldn't see anything wrong lots of pad drum in good condition nothing loose. The only thing I can think of is that the flat on the back of the drum is a bit rough (as it is not smooth and shiny like the rest of the drum) and is crabbing the magnet too hard.
I was going to try and loosen the brakes up a bit but they are self adjusting so there is no point trying that: well I will leave them loose so I can get the wheel back on anyway. I have just come home to get a multimeter to see what voltage is going to the wheel. Has anyone got some suggestions? Should I grease the magnet :o
Glenn

NOOOOoooo, no, no, no, no... don't grease the magnet!

These are the biggest PITA's when they're not working properly, so we'll do the basics first.
How old are the brakes, ie; have they worked OK before? If they're new, they do need to bed in. And even if they're not new, they are not self adjusting. Adjusting is critical to getting them right. This centralising and adjustment is my first step when diagnosing a problem. Jack up the axle. Loosen the 4 nuts mounting the backing plates to the axle. Tighten the adjusting screw till the drums lock hard, turning the drums as you adjust. Then tighten the mounting nuts, Then back off the adjuster till the drums just spin freely, but you can still hear them rubbing.

This would be my first thing to look at, as being out of adjustment is the biggest cause of locking with minimal power from the controller. If this persists after adjustment, then check what output the controller has, and whether the wiring joins aren't faulty.

Are the magnets earthed through the wiring, or to the chassis? I've had so many dramas with installers running a power wire to each of the magnets, and then earthing them to the chassis. Unless you have a perfect contact between terminal and chassis, you will get a different resistance from side to side, which will lead to poor/agressive braking on one side.

glenn k
1st Mar 2010, 07:23 PM
The brakes are both getting 9v to 4v depending on where the controler is set. I still have a GSL controller will replace with a Primus IQ that I have soon. On that I have a 24v to 12v converter on the truck that is on when the ignition is on can I power the Primus IQ with this or will it loose its settings when the ignition is turned off like the GSL does?
The trailer is 1997 vintage but it has not been used a lot so I would assume the brakes are original still have plenty of meat on them and the drums are not very worn. The brakes have been grabby since I got it but the truck was just running 12v to the brakes, no controler. It has been locking up since the GSL controler was put on but only on one wheel. The other brake works but doesn't lockup. Will try your centralising idea tomorrow hope it is the problem. I have no idea of the history of the brakes as it was a council chipper in QLD.
Is it possible that I will need to get the back of the brake drum machined to make it smother? It is not that bad though.

Yonnee
1st Mar 2010, 10:24 PM
Unless there's deep scoring of the magnet face of the drum, then I wouldn't worry too much about getting it machined up just yet.
From what you're telling me, I'm reasonably confident that centralising them should fix your problem. If you've measured both sides at the same voltage, then it is a mechanical problem. Let me know how it goes with the adjustment.

glenn k
19th Mar 2010, 07:42 PM
Well after I loosed the brakes and pulled the wheel off all looked fine put it back loose as the brakes have a self adjusting thingy that winds the adjuster one click every time you brake untill it is tight enough to not be able to engage again.
Well since then it hasn't locked again. I have now put the primus IQ on. It is powered by a centre tap between the 2 batteries (24V) it is triggered by a wire at the rear of the truck that comes from a converter that converts all the trialer lights 24 to 12 as the trailer plug is all 12v.
Well all works well brakes come on and I can adjust the voltage. The controler is constantly powered but 24 hours a day while driving and when left the thing flashes SH short circuit. Unless I'm braking then it tells me the voltage and works fine. I assume it must be getting some sort of feed back from the converter that makes it think there is a short. Is this a worry? What can I do about it? I assume the flashing and the unit constantly powered uses very little current.

Yonnee
20th Mar 2010, 09:15 AM
Firstly, It's not that I don't believe you, but I've never seen a self adjuster on an Electric Brake assembly. There is an adjuster at the bottom, accessed by removing the plastic plug at the bottom of the backing plate.

As far as testing for the short, you really hav to start at the front of the trailer. Remove trailer plug and see if display changes. Should flash 'n.c.' for 15 seconds then revert to ' . .'. If that's OK, then you need to start disconnecting magnets. Do this one at a time until you find which magnet is causing the "Short".

How old are the brakes on the trailer? How worn are the magnets? There should be grooves or dimples all over the face of the magnet. These are depth guages to show you how worn they are.

glenn k
20th Mar 2010, 11:31 AM
They are not ordinary trailer brakes Yonnee I would say they have14" drums. I was pulling a brake shoe back and and letting it go and watching the thingy turn the adjuster wheel.
It never accured to me that it may really be a short and the 24v GSL controler didn't show a short, and both brakes work. The controler says .. when the chipper is not on. As it is constanly powered and I pull the plug out I don't know about the nc bit. I will chec that out and look for a short in the brakes.
Thankyou Glenn
Yep pull trailer plug flashes"nc". Pulled the plugs on both magnets both read ~4 ohms and show no eletrical conection between magnets and brake drum.
Think it must be something funny with the voltage reduction or that it's powered by a centre tap but switched by a voltage that is derived from both batteries. The wiring on this truck is a mistery to me, there is a very large 24 to 12 unit that I tried to tap but it doesn't work, looks like they used a centre tap instead of replacing it. At the back of the truck there are several relays and a voltage converter with lots of wires. The wire that powered the eletric brake pin in the truck plug (at 12V only) came from a relay I used this to trigger the Primus IQ unit. I suppose the flashing "SH" deosn't matter as the brakes work and I can tell at a glance that the plug is in; or am I wrong?

Yonnee
21st Mar 2010, 11:00 AM
Like I said, It's not that I don't believe you, I've just never come across it. There are some wierd and wonderful (and some not so wonderful) adaptations out there fitted to trailers. All sorts of car stuff, modified and fitted to trailers and caravans. I'd be interested in seeing a picture of your brakes next time you've got them apart.

Back to the problem...
Did you pull one magnet at a time and then check the controller? Troubleshooting requires methodical testing and rechecking of each component. If the magnet has worn down so that the wires are shorting on the drum, the controller will show a short, but when you test the magnet with an Ohm meter, it can still show you the correct resistance. Or the magnet could have a fault and be shorting to the body of the magnet, without being worn, which will still show a short at the controller, but still measure correctly when testing the wires of the magnet.

I wouldn't be too worried about the truck side of things for now. The 'S.H.' is only detected through the output side of the controller... so basically, the blue wire that comes out the controller, all the way to the magnets themselves. So the short could be anywhere along that line, in the truck, or the trailer. You've already eliminated the truck by removing the plug, and the 'S.H.' disappeared. If it does the same with both magnets disconnected, but the trailer plugged back in, then it's unlikely to be the wiring on the trailer down to the magnets. Plug one magnet back in and check the controller. Then disconnect that magnet, plug the other in and check the controller again. If one of the magnets show the 'S.H.', then we're on the right track.

If neither magnet shows the short individually, but they do both together, then I'd try and find someone with another Electric braked trailer, and plug it into your truck and see what the controller says. If it still shows a short, then it could be a faulty controller.

glenn k
21st Mar 2010, 08:43 PM
I was sure it wasn't the brakes after checking for shorts to drum but checked again. pulled off both magnets still SH then pulled off the wire that triggers the unit that is conected to a relay that is fed from the centre tap and trigered by the red wire coming out of the 24-12 converter with lots of wires. Still SH, so I put it back.
Then removed the blue wire from trailer plug still SH :C so I put it back.
Then removed the red wire from plug:doh: SH gone checked and it is the stop lights they didn't work then reconected and they work again:rolleyes:
I have no idea how these 24-12v converters work; but maybe it's confused with the centre tap powering the brake unit??
It maybe something very simple but I can't work it out. My thoughts were the earth is bad; as this can make the unbelievable happen. But all lights and brakes work but I will check that next time.
Any ideas:?

glenn k
23rd Mar 2010, 05:57 PM
Now this controler has got confused. It usually flashes SH and works fine. Today it said nc while driving then back to SH. Then while stopped nc then c then back to SH so maybe the unit is faulty is there an easy way to check?

Yonnee
24th Mar 2010, 01:08 PM
Only by checking it against another trailer with Electric brakes first, and if it's still playing up, put it in another tow vehicle already set up with a unit (all the wiring will hook straight up). Or you can bench test it, but it's a bit mucking around and a bench test might not show up any intermittent faults.