TheSamba.com :: View topic - Bent or distorted drum brake backing plate

Fri Oct 23, 2015 2:37 pm

Went to inspect my drum brakes in search of a weird worbling noise that changed with rate of rotation of tires.

Drive side backing plate is warped/bent inboard behind bearing housing.
Distortion is 1/8"-1/4" out, or so, from the front which appears to remain in line with the drum casting.
Backing plate is flush to bearing housing as it should be.

Front brake shoe is evenly worn.
Rear brake shoe is worn as would be expected with the backing plate warped inward. The rear shoe shows an uneven angled wear.

Anyone experience this?

Possibly due to overheating drums?
What else contributes?

This may all explain a recently blown shock on the same corner, too. (overheated, perhaps?)

Thoughts?

Will post pics when I am back at the machine.

Fri Oct 23, 2015 3:20 pm

I am addressing the EXACT same issue with some brake drums from the classified section ( new) that are Centrex drums. I just ran them over to the machine shop and surfaced the rear edge .010 and just getting ready to install them. My shoe wear was good, new wheel cyl's etc.

Fri Oct 23, 2015 4:41 pm

Hiya newfisher!

Yes. I have had warped drums before.. on different vehicles.. turning them has done the trick a few times.

But in this case it is the backing plate, not the drum, that has noticeably warped.
That is the plate on which you attach the brake shoe pins, shoe pivots, brake cylinder, etc.

Although it is possible that the drum, too has been compromised.

Fri Oct 23, 2015 4:58 pm

Just back from a road test and all good. The aftermarket drums were too wide and after surfacing the edge or open face they are now not touching the backing plates around corners, building heat and scoring the plates. I recommend "turning" or surfacing any aftermarket drum or rotor before installing them, but have never had a set that were just wide enough to touch and need the lips machined to fit.....weird

Fri Oct 23, 2015 5:10 pm

So here's a shot of the backing plate in relation to the drum.
Drum is on hub flush.. but note that the backing plate flange/lip pulls away from drum to the back. (or to the bottom of frame)

Here is the uneven wear to shoe that is either the cause of, or the result of, the backing plate warpage..

No signs of contact between backing plate and drums.
Anyone?

Fri Oct 23, 2015 6:46 pm

Couldn't the backing plate simply be flattened out? I bet someone got in there with a pry bar at one point. I'd do it in the press personally just for the control factor. But one could also remove the drum, get behind it with the BFH and go to town. Not sure why it's making the weird noise, I'd think really the only issue with that would be shoe wear.

Have no idea what would cause that except if it got knocked or pushed somehow. Upon further review of the photo I see no marks from a pry bar. So this is something that happened since you've owned it?

-Kevin

Fri Oct 23, 2015 7:08 pm

61Scout wrote: Couldn't the backing plate simply be flattened out? I bet someone got in there with a pry bar at one point. I'd do it in the press personally just for the control factor. But one could also remove the drum, get behind it with the BFH and go to town. Not sure why it's making the weird noise, I'd think really the only issue with that would be shoe wear.

Have no idea what would cause that except if it got knocked or pushed somehow. Upon further review of the photo I see no marks from a pry bar. So this is something that happened since you've owned it?

-Kevin
Hey Kevin.

Correct..
Have owned this van for 12+ yrs.

No weird pry marks.. And the backing plate is safely tucked well inside big steel wheels.. I simply can not imagine how it could have been yanked on.
Its not been to a shop in years.
I do all the work.

It is something that has occurred in the last few months..
I assembled/reassembled these brakes twice some 2 yrs ago... fiddling to get better shoe contact to the new drums. Both were new at the time.
And they ran perfect for some time.

I initially put those backing plates on those Burley 16s.
They are original to this van and were in near perfect condition when installed on the Burley 16s 2 or so yrs ago.

I can't even think of how heat could have done it.. The heat goes to the drum itself, mostly.. and there is minimal contact to the backing plate from the shoes.. They "float" in there.

Perplexed.

I will likely order a new plate.. Van Cafe had them last time I looked.
But I don't want ti happening again.. These go for 90 bucks or so.

More disassembly is in order..

-jim

Fri Oct 23, 2015 7:14 pm

The hydraulics from the wheel cylinder itself would be strong enough to bend the backing plate. Same with the cable from the parking brake. But how that would happen is very strange indeed. Look forward to learning what you find out.

-Kevin

Fri Oct 23, 2015 7:22 pm

61Scout wrote: The hydraulics from the wheel cylinder itself would be strong enough to bend the backing plate. Same with the cable from the parking brake. But how that would happen is very strange indeed. Look forward to learning what you find out.

-Kevin
Something would have to be binding the shoe to do that.. yes.
I'll pull that shoe off and see what it shows.

Honestly did not think the hydraulics could manage that.. the shoe goes out flat to the drum.. Its supposed to "float" otherwise.

Something must be catching it and twisting the shoe under hydraulic pressure, maybe?

Sat Oct 24, 2015 6:47 am

Possibly the adjuster shaft was installed backwards.
This applies pressure in an assymetrical way and shows in your pad wear.

Fri Oct 30, 2015 10:25 am

So.. I received a pair of refurbished backing plates in the mail and proceed to tear down the old.

Here's what I found:

Photo 1..

the raised "slide" area of the backing plate.. where the shoe floats, was pushed out and actually torn and/or rusted thru.

I had not seen this damage before.. and the hole looks much older than 1 or 2 yrs.. Perhaps I missed this in previous servicing..

Photo 2..

Along the flange is another hole.. Looks intentionally made.
This may be a problem that has roots to previous ownership.. 12+yrs ago?

Can not tell cause and effect, here.
Obviously the backing plate shows abnormal wear.. but did that happen before the plate bent? Most likely.
Was the shoe catching on that worn area and not returning to its "floating" position. Possible..

Also worth noting.. the bearing stinks of burning.. I wonder what else lies waiting! Dragging shoe over-heat the bearing?

More work lies ahead.