Brake magnet scoring drum |
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offgrid
Senior Member Joined: 23 Jul 2018 Online Status: Offline Posts: 5290 |
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Topic: Brake magnet scoring drum Posted: 12 Jun 2022 at 9:54am |
Lippert has it right. When you initially set up drum brakes (on any vehicle) that is how we adjusted them back in the day, just a sight drag. You do need to engage them a couple of times while spinning the when when adjusting them to be sure the brake shoes are centered up on the drum.
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1994 Chinook Concourse
1995 RV6A Experimental Aircraft 2015 Rpod 179 - sold |
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Welchsoft
Groupie Joined: 08 Jul 2020 Online Status: Offline Posts: 58 |
Post Options Quote Reply Posted: 12 Jun 2022 at 5:56am |
At the moment, brake units, hubs and bearings are new. Wheels turn about a complete revolution before stopping. Burnishing is not completed yet but drove about 20 miles with everything new and braking seems to be equal on both wheels. On a side note, my part time mechanic worked on RV's ad a dealership for quite a few years and helped me with the problem. He said that when you burnish new brakes, they need an initial adjustment that prevents the wheel from turning no more that one half turn. When I called Lippert, they said the wheel should spin with just a slight resistance and you could hear a small amount of contact to start the burnishing process with.
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offgrid
Senior Member Joined: 23 Jul 2018 Online Status: Offline Posts: 5290 |
Post Options Quote Reply Posted: 09 Jun 2022 at 4:45pm |
I assumne these are pics of the the old brakes you replaced? There does seem to be quite a bit of wear on these. The wheel mounting studs should be recessed in the hub/drum but it looks like either they weren't recessed enough or the steel surface has been worn down till they are starting to get wear from the magnet.
Do the wheels turn freely now with the brake controller on but no braking activated? |
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1994 Chinook Concourse
1995 RV6A Experimental Aircraft 2015 Rpod 179 - sold |
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Welchsoft
Groupie Joined: 08 Jul 2020 Online Status: Offline Posts: 58 |
Post Options Quote Reply Posted: 09 Jun 2022 at 8:15am |
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Welchsoft
Groupie Joined: 08 Jul 2020 Online Status: Offline Posts: 58 |
Post Options Quote Reply Posted: 09 Jun 2022 at 8:10am |
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offgrid
Senior Member Joined: 23 Jul 2018 Online Status: Offline Posts: 5290 |
Post Options Quote Reply Posted: 09 Jun 2022 at 7:41am |
Some scoring is normal, the magnets make contact with the drum surface when they are energized. It's the friction of that contact that activates the brake shoes.
But I'm not sure if what youre describing is normal or not. The contact shouldnt be producing metal shavings for example. Do you have any pics of the scoring? A bad contact would make one magnet deenergize so that brake stopped making contact but it wouldn't cause scoring. Quite the opposite. I'd recommend getting rid of the insulation displacement connectors on the brake wiring and replacing them with butt splices or soldered connections and heat shrink tubing. The factory connectors are junk. |
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1994 Chinook Concourse
1995 RV6A Experimental Aircraft 2015 Rpod 179 - sold |
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Welchsoft
Groupie Joined: 08 Jul 2020 Online Status: Offline Posts: 58 |
Post Options Quote Reply Posted: 09 Jun 2022 at 6:57am |
I'll pick up an IR thermometer. Just wish I could have had a definitive answer as to why the magnets are scoring the drums. My thought is that a bad ground or loose connection might cause one magnet to be energized more than the other while the trailer is bouncing down the road. Just don't know.
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offgrid
Senior Member Joined: 23 Jul 2018 Online Status: Offline Posts: 5290 |
Post Options Quote Reply Posted: 08 Jun 2022 at 3:55pm |
Glad you have it sorted out now. For sure the burnishing process gets the brakes pretty darn hot.
If you do the math it works out that the drums will heat up by about 300 degrees above starting temp if you use the trailer brakes alone to fully stop the rig from freeway speed. Lippert has you do up to 50 gentler decelerations from 40 to 20 and wants you to get the drums up to around the same 350-400 degrees. Safer and more controllable that way. I carry my ir thermometer in my tow vehicle arm rest and check bearing and tire temps while refueling, and brake temps once in awhile after making a full stop from freeway speeds or after a downhill grade. Great tool which can give you early warning of several potential problems. |
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1994 Chinook Concourse
1995 RV6A Experimental Aircraft 2015 Rpod 179 - sold |
|
Welchsoft
Groupie Joined: 08 Jul 2020 Online Status: Offline Posts: 58 |
Post Options Quote Reply Posted: 08 Jun 2022 at 2:46pm |
Both magnets are within specs on amps and ohms. A friend checked it out and suggested that the brakes were not adjusted equally for brake-in and with the initial adjustment the wheel (jacked off the ground) should only do about a half of revolution, then you need to drive quite a bit applying the brakes until they settle in. Replaced the hub what was slightly scored and the associated magnet. Right not the brakes are pulling evenly and I had no idea just how hot the acceptable temperature was for the hubs during brake-in. Time will tell. Thanks for the help.
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Welchsoft
Groupie Joined: 08 Jul 2020 Online Status: Offline Posts: 58 |
Post Options Quote Reply Posted: 04 Jun 2022 at 1:03pm |
Thanks. Amps with the car running. L:.14, R:1.45. While I see a big difference, still not sure about the measurement as I would expect the problem L site to be getting more not less than the R. I'll test again with the battery.
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