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post #1 of (permalink) Old 12-05-2005, 02:02 PM Thread Starter
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Drum brake experts

AMC 20 Rear Axle

I replaced the drums and shoes a few months ago. It seemed that ever since whenever I let off the gas and coast I have a click, click, click then it goes away when I apply the brakes. I tore it apart about a week ago and I had deep imprint into the backing plate on the passenger side. Ground it flat and reinstalled everything and it is still doing it.

I think I either have something backward like the shoes or misadjusted brakes. I looked at the shoes and I couldn't tell the thicker trailing shoe from the other except by the different setup points or notches or whatever they are called. I believe I have it installed correctly as per FSM manual but who knows.

All u-joints fully greased and checked with no issues. Rear axle bearing are new and freshly packed as I thought I had a bad bearing. Doh! Bearings good.

I am confident it is a rear brake issue. E-brake works fine and stopping is not an issue at all. I just have an annoying and possibly damaging noise when coasting and it goes away when I brake. How can I resolve this.

This stupid AMC 20 axle is pain in the butt with the two piece axle and the necessity to pull the hubs to grease the bearing. Only if I had the funds I would put the Scout axle I have in the basement in. I hate being broke.

BTW, the two piece axles are in good condition if that matters.

I need help with these darn drum brakes. This has had to been a headache someone else. Search was no help.
Enlighten me. Please.
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post #2 of (permalink) Old 12-05-2005, 02:19 PM
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Re: Drum brake experts

Hard to explain in words how the Drum brakes go togehter, but if your parking brake works, then you have the shoes on the right side..... so long as you didn't mix left side and right side. Quick check on that is the aft shoe has the ebrake lever on it and it goes on the inboard side. I'd imaigne you'd have a hell of a time getting them backwards, but you never know [img]/ubbthreads/images/graemlins/grin.gif[/img]

as for clicking.... I can't imagine anything that would click lke you're talking about. But a notched area on the backing plate.... was it there before you changed your brakes? did you fully seat your brake shoes on the post at the top of the backing plate. I like to smear a little anti-sieze on the backing plate where the shoes ride. shoould be two raised areas for each shoe on the backing plate.

As for the bearings, no, you don't have to pull the hub. Infact, I'd advize against pulling the hub. they are (from all I've HEARD) presed on from teh factory with 20 tons. I'd pulll the axle before I pulled the hub. Once you disturb that hub you're only asking for a spun hub.

Oh, and don't knock that AMC20 too hard, It's got a bad rap, but it's a decent axle with some one pieces, besides, i bet those scout axle brakes are the same just a different size. [img]/ubbthreads/images/graemlins/wink.gif[/img]
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post #3 of (permalink) Old 12-05-2005, 02:46 PM
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Re: Drum brake experts

The metal part of the brake shoes are indentical, primary or secondary. The difference isn't the thickness, but the length of the friction material. The ones with the LONGER friction material goes TO THE REAR OF THE VEHICLE. If they are identical they are interchangable. The rear one does the majority of the stopping.

But that's not the click, nor is it the wear on the backing plate.

You had the drums turned. The yo yo that did it didn't finish the job. When he cut them, he used too fast a feed, it left a fine screw thread on the inside of the drum. He should have done a fine finishing cut, almost as a polishing cut as the last cut.

When your linings first touch, that thread he left in the drum surface pulls the shoe with it, then it slips, then pulls, slips, pulls, etc - click click click - and each time it wears the backing plate a little more.

Look close at the machined surface of the drum, you'll see the tiny threads.
Rough it up with emory paper - scratch it so the threads are no longer apparent.
File/grind the backing plate notches flat again, lightly lube the spots where the shoes touch the backing plate - enjoy.

BTW - the "lifetime" lining are trash. They are super hard material to last a long time. The cheapie linings are much softer, they don't last quite as long, but they do stop nice!

Brake manufacturors seem to have forgotten -- BRAKES ARE A FRICTION DEVICE!
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post #4 of (permalink) Old 12-05-2005, 02:48 PM
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Re: Drum brake experts

Thicker shoe goes to the rear.

When you press on the brakes, the shoes want to rotate the same dir as the drum. On the left side, that is counter clockwise....this pushes the shoe against the top stop just above the brake cyl.....the rear shoe basically gets wedged in there....I believe it does about 60% of the stoping.

How do you know the bearing is good?

Is the clicking coming from the same side as the worn backing plate?
Does the click happen in exactly the same pos of wheel rotation every time?
Are your brakes adjusted correctly?
Do you get a click when backing up?

If the clicking is caused by any brake componets, something in there will wear indication on it.

If you get the clicking only when you have weight on it, I would suspect bearings.
post #5 of (permalink) Old 12-05-2005, 03:03 PM Thread Starter
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Re: Drum brake experts

Drums were new I looked at them when I had them off so now I'll give them a closer inspection. The bearings are new. I even replaced one and now I have a handy spare because it was good. When I had it jacked up it still made the noise.

I think I'll take it all apart and go from there. Third times a charm.

It's pretty cold here so I'll try to get at it later this week and give you all an update.
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post #6 of (permalink) Old 12-05-2005, 03:20 PM
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Re: Drum brake experts

[ QUOTE ]
You had the drums turned. The yo yo that did it didn't finish the job. When he cut them, he used too fast a feed, it left a fine screw thread on the inside of the drum. He should have done a fine finishing cut, almost as a polishing cut as the last cut.

When your linings first touch, that thread he left in the drum surface pulls the shoe with it, then it slips, then pulls, slips, pulls, etc - click click click - and each time it wears the backing plate a little more.

[/ QUOTE ]

Now that's pretty good Rich! I hadn't heard that one. makes sence. Good info!
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post #7 of (permalink) Old 12-05-2005, 05:39 PM
 
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Re: Drum brake experts

Just for reference:
Driver side:


Passenger side:


Yeah I know, I don't have the auto adjusters installed.

Hmmm also forgot about one of those rattle springs on the equalizer bar.
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post #8 of (permalink) Old 12-05-2005, 06:22 PM
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Re: Drum brake experts

Put the adjusters back on. And put the spring back on.
Since you say the drums are new - were they turned? Lots of shops like to turn new drums or discs.
They seem to think their little $3000 lathe is more accurate than the multi million dollar machine that made them.

When you don't put all the parts back in as designed - you can expect problems. Most likely you don't have them adjusted right - way too loose.
Of course you did center them several times when you adjusted them - No? == The rattle.

I'm a believer in doing it right - once!
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post #9 of (permalink) Old 12-06-2005, 03:44 AM
 
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Re: Drum brake experts

[ QUOTE ]
Put the adjusters back on. And put the spring back on.
...
When you don't put all the parts back in as designed - you can expect problems. Most likely you don't have them adjusted right - way too loose.
Of course you did center them several times when you adjusted them - No? == The rattle.

I'm a believer in doing it right - once!

[/ QUOTE ]

Ummm. Those are my brakes, mine work great. I was just posting a picture of how the shoes go on.
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post #10 of (permalink) Old 12-06-2005, 07:03 AM
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Re: Drum brake experts

Tsk Tsk - you know better John.

Notice the linings on the shoes are different lengths, primary vs secondary, or leading vs trailing.

I "assume" both sides were replaced at the same time, and both have equal mileage on them?

Why is the lower picture's leading shoe worn so thin, while the other side the linings are the same thickness?
Looks like the lower side was dragging - adjusted too tight, while the other side was looser. One reason for having the self adjuster working properly, they keep both sides equally adjusted.

Normally because of the crown in the road, the right side wears slightly faster than the left. The self adjusters compensate for that. That's why when you inspect them, always start with the right side.
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