Strange Rear Drum Brake Noise

[cthomasparr]

I just replaced most of my brakes on my 2004 Vibe and there is one nagging issue that I cannot uncover. The rear drums make a thumping noise when I brake harder to come to a stop. If I slow more gradually, the brakes are quiet. In the rear I replaced the wheel cylinders, shoes, hardware and drums. Drums are Raybestos shoes Wagner. On the front I rebuilt the calipers and replaced pads and rotors. The brakes work well. No pulsation, no pulling. The rears are adjusted so the tires rotate freely, but the e-brake engages in about four to five clicks. If I do brake hard enough for the thumping/nocking noise to start it will match the wheel speed and pretty much continue until I come to a stop. I haven't been able to identify if it is coming from the left side, right side or both. I also really don't feel anything coming through the brake pedal.

Anybody have any ideas? I hate to leave it is as because it will be my daughter's car and when she drove it, it thumped every time she used the brakes

Not sure if it matters, but the car does have ABS. It doesn't make the typical ABS chatter noise when this happens and it continues all the way to a stop.

[Chiadog]

Have you tried braking just with the Emergency brake? This would isolate any thumping to the rears. It may be possible to remove ABS from the equation by pulling the fuse, but I'm not certain because I have very little ABS experience. I always do front/rear brake jobs separately, so I know where to look if problems arise.

[jolt]

Rear brakes making thumping noise with new drums. Were the drums trued/turned ? I have seen new drums that have been warped out of the box brand new. New/green castings can move around as the stress in the casting normalizes, which is why having your old drums turned can be a better option. It does not have anything to do with the brand of drum but with how the drums are stored before you bought them. Another thing to check are the backing plates. There are bumps in the backing plate that the brake shoes rest against when you put the hold down springs on. The shoes over time wear grooves into these pads on the backing plate. The new shoes could be catching in and out of these grooves in the backing plate. Before installing new brake shoes, the backing plate pads should be inspected. The pads on the backing plates need to be ground smooth to remove rust and any wear from the pads. Also check that the new drums are centered on the hubs and fit the hub snug. Are the hub to drum surfaces clean of rust and flat? I would set the shoes up with a light amount of drag to the drum, new brake shoes will wear in and mate up with the drums in a short amount of time. They need to knock the high spots off for full contact so starting them with a little drag is not going to hurt.

[cthomasparr]

Thanks for the replies. I guess my auto notification did not work otherwise I would have checked in sooner.

I don't think its an ABS noise because the wheel rotation speed is not irregular... no skidding. If it is ABS I have bigger issues. Also does not sound like ABS noises I am used to. There is no ABS modulator clicking going on up front.

I didn't inspect the backing plate very much.. should have checked and sanded down the contact points, but I did lubricate. I bet they are OK. I also think the drums might be the issue. I may take my original drums and get them cut at NAPA. Did that last time for about $12 each on my other vibe. Worked fine afterwards.

The only thing that makes sense to me is that the pads are being pulled away from the backing plate when they contact the drums and the green pad springs are pushing them back when they get compressed enough. This probably repeats until I come to a stop.

Hub to drum surface is a good thing to check.. I think it is good, but maybe I could check that out. the drums themselves are round, but I wonder if the braking surface is truly flat with respect to the brake pads or if the brake pads hit first at the outer edge.. that might explain my theory.

[cthomasparr]

I just got off the phone with Raybestos support and I was told that the machined finish on the new drums is like a "record player" that has fine grooves that can cause the shoe to move in and out. This pattern on the drum's braking surface can be removed by:
1. Continued use that will eventually wear the surface
2. Some kind of light cut on the surface by a machine shop. Cant remember the name he used, but not a full machining
3. Rub 80grit sandpaper in a swearly patten over the braking surface.

I will most likely try the 80 grit sandpaper when the weather clears here.

[Chiadog]

Thanks for this information! Semi-finished brake drums from Raybestos, did the support tech say WHY they don't complete the machining process?
Guess I'll be sticking to the lowest priced brake drums, Duralast, etc.

[jolt]

Some 3M sanding pads could make the sanding go faster. See link:
http://3mcollision.com/products/abrasiv ... 03050.html

I use these to knock the rust edge off the outsides of the rotors before removing brake pads. I do not think the surface finish is going to be the problem. Take the car to an open parking lot and go forward and reverse, back and forth braking at least 10 times coming to full stop in each direction. This should work the brakes shoes and the self adjusters so the shoes are set. The self adjusters have to be in the proper place with the proper springs when assembled for the self adjusters to work. Something else about self adjusters and brake shoe wear, on some systems have a primary and secondary brake shoe, one shoe will have less contact surface then the other shoe. These have to be in the proper location for the self adjusters to work. The best thing to do before taking anything apart is to take pictures so you can make sure things are back in the proper locations and holes.

If you adjust the shoes up with some drag on the drums and you try turning the tire to spin the wheel, does the wheel have even drag on it from the brakes? Does the drag go free and then get hard to spin the tire?

[cthomasparr]

I sanded the drum's braking surface with 100 grit paper enough to show visible swirls. To make it easier, I pulled the drum and mounted it with the drum facing out and hand tightened two lug nuts. I sanded and slowly turned the drum.

After replacing the drums, the noise has gone away. I did notice it during an emergency stop where I almost locked up the brakes, but that almost never happens. Overall I am happy with the drums and will probably give any future drums a good cleaning and sanding to never have this issue again. The drums that I had machined at NAPA did not have this problem, so I would guess machine shops are cutting these differently or have another step in the cutting process.