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Old 07-18-2004, 10:43 AM   #1
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Question Worn brake electromagnet?

While repacking the wheel bearings on my '67 Overlander, I noticed one wheel's electromagnet appears to be worn. I have never seen a new electromagnet, so I have no basis for comparison.

From what you can see in the following picture, what is your interpretation?

Also, when ordering parts for Kelsey-Hayes brakes, I noticed the parts are offered for 10" and 12" brakes. Does this dimension refer to the inside diameter of the drum?

Thanks,
Tom
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Old 07-18-2004, 11:15 AM   #2
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I have heard that if the magnet is worn to the tops of the screws it is time for new ones. The Round magnets are no longer made, they make them oval now. The oval ones will have more braking power co you will need to replace both sides, but they should both be wore out anyway

I don't know if the dimension is the inner or outer DIA of the drum, someone else here will know for sure.
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Old 07-18-2004, 01:15 PM   #3
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Magnets worn to the screw heads are in need of replacement, as they rub on the side of the drum, creating friction which forces the shoes out to the drums. 10" and 12" refers to the inside diameter of the drums
Magnets are indeed now available only in oval, supposedly they work better, and both magnets on that axle will need to be replaced to equalize braking power.
Shoes should not need replacement as long as there is a minimum of 3/32" usable friction material left, new should be 10/32". I would replace if it was less than 5/32", so you don't have to go back in and put shoes on in six months.
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Old 07-18-2004, 02:22 PM   #4
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I have ovals on the front axle and rounds on the back. Fronts seem to run hotter with the ovals, maybe they are not broken in yet.
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Old 07-18-2004, 02:38 PM   #5
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Quote:
Originally Posted by Pick
I have ovals on the front axle and rounds on the back. Fronts seem to run hotter with the ovals, maybe they are not broken in yet.
Ya know Pick, I think you mentioned this in another thread which dealt with IR temperature detectors. Are you sure your Airstream is riding level going down the road? If it was pitched forward a bit, the front axle bearings would run a bit hotter.

Just a thought,
Tom
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Old 07-18-2004, 02:46 PM   #6
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Quote:
Originally Posted by argosy20
Magnets worn to the screw heads are in need of replacement, as they rub on the side of the drum, creating friction which forces the shoes out to the drums. 10" and 12" refers to the inside diameter of the drums
Magnets are indeed now available only in oval, supposedly they work better, and both magnets on that axle will need to be replaced to equalize braking power.
Shoes should not need replacement as long as there is a minimum of 3/32" usable friction material left, new should be 10/32". I would replace if it was less than 5/32", so you don't have to go back in and put shoes on in six months.
Terry,

You are just plain "Da Man!" I appreciate having some actual thickness measurements to go by.

My linings appear to be in good shape, so I lean toward just replacing the electromagnets. Do you know if the ovals will "simply" pop in in place of the antique round ones? I ask because there are no trailer shops nearby to stop & compare parts.

Thanks,
Tom
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Old 07-20-2004, 12:37 PM   #7
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I think you need new backing plates

I have heard that if you want to upgrade to the newer oval magnets from the round, a complete backing plate designed to accomodate them is required.

I could be mistaken about this - can anyone clarify?
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Old 07-20-2004, 12:40 PM   #8
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Originally Posted by coriolis1
I have heard that if you want to upgrade to the newer oval magnets from the round, a complete backing plate designed to accomodate them is required.

I could be mistaken about this - can anyone clarify?
I believe that is correct. But etrailer.com still sells the round magnets.

Tom
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Old 07-20-2004, 12:44 PM   #9
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I just bought a set of round magnets from Inland RV, thus avoiding the need to change the backing plate.
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Old 07-20-2004, 12:52 PM   #10
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Ah, okay. Good to have the info out there so that folks with round magnet assemblies don't mistakenly think that they can go buy oval magnets for 'em (or vice versa). Nothing like having an extra trip to the parts house cut into our already precious weekend refurb time.

Anyone had their drums turned while they were off? Can a shop that turns auto rotors and drums handle these with no trouble?
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Old 07-20-2004, 12:57 PM   #11
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Quote:
Originally Posted by coriolis1
...Anyone had their drums turned while they were off? Can a shop that turns auto rotors and drums handle these with no trouble?
I'm willing to bet a shop could turn out bad places on the brake shoe surface area, but they probably cannot do the perpendicular magnet surface area.

Tom
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Old 07-20-2004, 06:28 PM   #12
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Quote:
Originally Posted by coriolis1
Ah, okay. Good to have the info out there so that folks with round magnet assemblies don't mistakenly think that they can go buy oval magnets for 'em (or vice versa). Nothing like having an extra trip to the parts house cut into our already precious weekend refurb time.

Anyone had their drums turned while they were off? Can a shop that turns auto rotors and drums handle these with no trouble?
I have done it on my brake lathe at my shop, but the average auto mechanic or parts store help won't be able to do it. Turning the friction part the shoes ride on isn't a problem, but the vertical part the magnets ride on is.
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Old 07-20-2004, 06:58 PM   #13
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Quote:
Originally Posted by Pick
I have ovals on the front axle and rounds on the back. Fronts seem to run hotter with the ovals, maybe they are not broken in yet.
If the brakes with oval magnets generate more braking force, those brakes should get hotter. More friction = more heat.

Bob
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Old 07-20-2004, 10:47 PM   #14
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Originally Posted by argosy20
I have done it on my brake lathe at my shop, but the average auto mechanic or parts store help won't be able to do it. Turning the friction part the shoes ride on isn't a problem, but the vertical part the magnets ride on is.
Terry

Sounds like I'll need to get on the phone to some of the machine shops here in town - someone's bound to have turned some of these somewhere...

Would think that an outfit capable of turning things like flywheels and such would know how or know someone who does. I'll check around here and see.

Thanks for the info, guys.
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Old 07-21-2004, 10:45 AM   #15
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Pick.

You "MUST" not mix the two different style backing plates.

To do so, causes the oval brake to carry more braking weight than it should, and that's assuming you have both brakes adjusted correctly.

Further, by having different braking effiency on the two axles, may also cause abnormal tire wear, since one axle is doing more stopping than the other.

Not a good idea to mix different style brakes.

Round brake magnets are still available.

Andy
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Old 07-21-2004, 12:06 PM   #16
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Considering that a backing plate for 12" brakes can be had for something like $60 it can make good sense to go this route.

If one magnet is worn, the others are suspect, too, and their cost is a good chunck of the cost of an entire backing plate.

The backing plate gets you magnets, shoes, springs, and all the other moving brake parts.

The backing plate is a simple install (although I have heard conflicting stories about whether the hub braking surfaces need turning) - this ameliorates labor costs which tends to even out overall costs.

So I am looking at new backing plates in a year or two on my 30 year old. Am I missing something?

Thanks Andy for the not mixing note - hadn't considered that one.
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Old 07-21-2004, 12:20 PM   #17
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Originally Posted by Leipper
...The backing plate is a simple install (although I have heard conflicting stories about whether the hub braking surfaces need turning) - this ameliorates labor costs which tends to even out overall costs...
Hopefully it is a simple install. I was at an SOB dealership the other day picking up common parts, and noticed they had backing plates on the shelf. Now, it might just be the brand they carry, but the man helping me told me that everything mounted on the backing plate would work on my Airstream, but the backing plate itself would not. I would need to transfer the stuff from one backing plate to another.

I tended to trust him because although he works for an SOB dealer, he tows an Airstream

Just be careful that the loaded backing plates you buy will fit your axles.

Tom
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Old 07-21-2004, 03:40 PM   #18
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Brake backing plates will fit all but the oldest of drums.

When the drum hits the backing plate, have a machine shop take about an 1/8 to 3/16 of an inch off of the inner lip.

Then have a beer, cause the problem is gone.

Andy
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Old 07-21-2004, 04:32 PM   #19
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Brake backing plates will fit all but the oldest of drums...
Trust but verify
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Old 07-22-2004, 07:01 PM   #20
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For the archive

Just came in today:
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