Rear drum brakes vibration - any ideas?

MikeWhitney · **Joined:** Wed Aug 20, 2003 9:15 pm **Posts:** 4724

I've been trying to troubleshoot a nagging brake vibration on my 97 Subie. Feel the vibration in the seat, floor, and pedal, exactly like the feeling of a "warped" front disc. Replaced front discs, no improvement, then replaced the rear drums, no improvement. The vibration is worse when hot.

Now I know it's coming from the back axle, since I discovered that the vibration can be created by pulling the e-brake.

When I replaced the drums I checked the linings, cylinders, and springs out, everything is in fine working shape, nothing binding or worn out. I cleaned everything with brake cleaner and sprayed the sliding points with some dry-lube.

No changes, still vibrates the same under braking when hot. Any idea?

George Bright · **Posted:** Mon Jun 12, 2006 5:04 pm

Try this
If you can bolt the drum on inside facing out. rotate it with a dial indicator on the inner surface to check for run out. I would also check the hubs for run out. Do your rear wheel bearings have enough preload at this mileage? I don't know if you have half shafts or not. I would also check the U joints or CV joints for play.

MikeWhitney · **Joined:** Wed Aug 20, 2003 9:15 pm **Posts:** 4724

George Bright wrote:

Try this
If you can bolt the drum on inside facing out. rotate it with a dial indicator on the inner surface to check for run out. I would also check the hubs for run out. Do your rear wheel bearings have enough preload at this mileage? I don't know if you have half shafts or not. I would also check the U joints or CV joints for play.

Definitely good ideas George... I do have a dial indicator that I have never used, this is a good chance to try it out.

The car is AWD so it has half-shafts and they may be original with 219k on them. I also need to see if the bearings are sealed cartidges or actually adjustable.

So any idea how would play in the CVs or hub looseness cause vibrations only under "warm" braking?

George Bright · **Posted:** Tue Jun 13, 2006 4:37 pm

The only thing I can think of is that warming up the hub and brakes may cause the bearings to expand and loosen up. ALso cold greese may dampen vibration where as warm thinner greese may not. (long shot)

My old 510 had some vibration under braking. It went away when I swapped out the half shafts for units with new U joints. One of the U joints was about to come apart. It may have been from the angle the shafts were running at with no load and braking.

Chuck Frank · **Posted:** Fri Jun 16, 2006 9:30 am

My guess would be a warped or glazed drum if the hub runs true. Since drum brakes have near disappeared some of the care were could recite by rote years ago has been forgotten:
never put on the emergency brake when parking after driving for a period of time. Lightly apply the brakes just before and hold while driving thru an unexpected wet area (not only during a rainstorm but on dry days like the day after a heavy rain or around construction etc.) to reduce shocking the hot drums and to dry the shoes. Unlike disks, the shoes on drums are not continuously in contact with the drums to help disapate the heat buildup and the centers are rather thin so it's easy to warp them. Applying the emergency brake on hot drums can warp a hot drum and/or transfer friction material to the drum. Examine the inside surface for heat checks or color differences. Drum brake shoes and turning of drums is pretty cheap, and should be done together.
One other thing does it have ABS?

MikeWhitney · **Joined:** Wed Aug 20, 2003 9:15 pm **Posts:** 4724

Chuck Frank wrote:

My guess would be a warped or glazed drum if the hub runs true. Since drum brakes have near disappeared some of the care were could recite by rote years ago has been forgotten:
never put on the emergency brake when parking after driving for a period of time. Lightly apply the brakes just before and hold while driving thru an unexpected wet area (not only during a rainstorm but on dry days like the day after a heavy rain or around construction etc.) to reduce shocking the hot drums and to dry the shoes. Unlike disks, the shoes on drums are not continuously in contact with the drums to help disapate the heat buildup and the centers are rather thin so it's easy to warp them. Applying the emergency brake on hot drums can warp a hot drum and/or transfer friction material to the drum. Examine the inside surface for heat checks or color differences. Drum brake shoes and turning of drums is pretty cheap, and should be done together.
One other thing does it have ABS?

It does have ABS. Hwo do you think this could affect it?

I replaced the drums w/ new ones, same vibration from the first time I used them. That pretty much eliminates the drums themselves from the equation.

Chuck Frank · **Posted:** Fri Jun 16, 2006 1:51 pm

ABS will sometimes pulse the pedal even at low pressure, my Taurus did the same thing. Don't know if it's a characteristic of the ABS system programming or something out of whack with a sensor?

The guy you want to ask is Cortney Cormier out of VMSC club.

MikeWhitney · **Joined:** Wed Aug 20, 2003 9:15 pm **Posts:** 4724

Chuck Frank wrote:

ABS will sometimes pulse the pedal even at low pressure, my Taurus did the same thing. Don't know if it's a characteristic of the ABS system programming or something out of whack with a sensor?

The guy you want to ask is Cortney Cormier out of VMSC club.

Ah, I see. It's definitely different than ABS vibration. Something is definitely our of round/warped/etc. The vibration was occurring before I fixed the ABS as well.

Hopefully I'll get the car on the lift this weekend and start doing some tests.

George Bright · **Posted:** Fri Jun 16, 2006 4:36 pm

Warning New drums do not mean they are true. Been bit by that one before.

Brad Mackey · **Posted:** Mon Jun 19, 2006 9:10 pm

Drum brakes can easily float around in there, so it probably isn't the brake system.

Possible bearing problem, but not likely, unless you hear some other noises.

Check the CV Joint. Looks like a good place to start

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Rear drum brakes vibration - any ideas?

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