Scraping sound from rear end

Maintenance/Repairs
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1

Hello,

I am in the process of finishing up a muffler change on my 2010 Grand Caravan and have a new issue. I don’t know if it’s related to the repair or not.

I am hearing a scraping sound from the rear end that can be heard at low speed. It sounds like part of a wheel is scraping on something in that the sound is only audible during part of a revolution. The rate of the sound changes with speed. I cannot hear it at speeds > 30 mph but it may just be that at this speed the sound just becomes continuous and fades into the background.

I have looked underneath and there isn’t anything touching the wheels. I have had both rear tires off and nothing looks out of place. If I spin the rear wheels, there is a definite scraping sound from the rear brake pads on the rotor. I don’t know if the caliper piston has not retracted far enough or not. If this were the source of the sound I would expect it to be a continuous scraping sound and not the chug, chug, chug I am hearing.

Also, I can smell a burnt rubber smell when I get out after driving a while. Both the sound and the smell seem to be coming from the drivers rear. I am not sure it has anything to do with the recent muffler replacements since the exhaust runs down the passengers side.

I did top off the brake fluid yesterday as it was not all the way to to the top.

There is not really much happening at the rear end of these vans so it’s hard to guess what the issue may be. The rear brake hardware, calipers, wheel bearings, and dust shields are relatively new. The rear shocks are piles of rust but they are not close enough to anything to rub.

Any suggestions as to where the sound or smell may be coming from? Any ideas as to what to try next?

LMHmedchem

2

What you might be hearing is the brake pad wear indicator touching the brake rotor.

You can see the brake pad wear indicator in this image.

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But to find out if that’s the case, you’d have to do a brake inspection.

Tester

3

Thanks, I looked at the pads from the top and they look fine. I have seen cases where there was uneven wear and the pads looked ok on one end but were worn down on the other.

I guess I will have to pull the calipers off to check that.

Any idea about the burnt rubber/plastic smell? Is there part of the pad that could smell like that if it overheated from friction?

With an older vehicle it can be hard to tell if you are looking an issue with multiple symptoms problem or two separate issues.

LMHmedchem

4

Did you put the Permatex on the exhaust?

Tester

1 Like
5

No, not yet (with the Permatex).

It has been raining pretty hard and I am also waiting for a new rail guard for my jack. I really dislike jacking up these vans that don’t have a frame. I always think that something is going to crumple. It’s really hard to find both a good jack point and a good place to put a jack stand.

LMHmedchem

6

Get a pinch weld jack pad to lift.

image

And pinch weld jack stand pads to support.

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Tester

7

The smell could come from oils being burned off of a new muffler or sticking brakes due to sticking slide pins, caliper or bad brake hose. Make sure dust shield isn’t rubbing on rotor.

8

What you might be hearing is the brake pad wear indicator touching the brake rotor.

Would this be a continuous scraping sound? I am hearing an intermittent scraping sound with a frequency that matches the wheel speed. Is that what I would expect from the wear indicator?

Get a pinch weld jack pad to lift.

This is what I am waiting on, though I have always called it a rail guard because it protects the steel rail that the scissor jack fits to. This is the one I ordered,

DIY Car Universal X-Slot Rubber Frame Rail Adapter ($15)

I will look into the fittings for the jack stands. I have rubber caps for those but not the kind that fits around the rail.

The smell could come from oils being burned off of a new muffler

Is that typical? It would be nice if that was all it was.

The smell could come from … sticking brakes due to sticking slide pins, caliper or bad brake hose. Make sure dust shield isn’t rubbing on rotor.

The rear calipers are pretty new (a year or so I don’t remember), as are the rotors and dust shields. I had to replace the rear hub and bearing assemblies so I did the shields at the same time. This is the idiotic design where you have to remove the hub to change out the dust shield so it seemed shortsighted to not do it when I had the chance.

I didn’t change out the flex hoses since I didn’t want to fool with the hard lines. The metal is rusty but they look fine otherwise. What should I look for there other then a leak?

Even so, I will take off all 4 calipers and do a close inspection. I will also spin the tires as fast as I can and see if I can replicate the sound at one of the wheels. I think that the sound is from the rear but I have been fooled before.

…that is, I will do all that if it ever stops raining.

LMHmedchem

9

Tester

10

I agree with Tester if you are lifting vehicle from pinch weld. I use these to lift my car in the front.

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11

Over the last 2 days I carefully went through the rear end to see if I could identify the issue causing the sound.

These are the steps I went through for both sides

  • jacked up the van using the frame rail adapter (that worked well)
  • placed a jack stand on the large bracket that the rear end mounts to
  • placed the jack under the rear end and jacked the wheel up to ride height
  • placed a second jack stand under the rear end to maintain ride height
  • spun the tire as fast as I could get it to go to try and replicate the sound

Both tires spin freely and I cannot replicate the shus-shus-shus sound that I hear at low speeds. There is a continuous scraping sound from the brake pads on the rotor, but this is continuous, not a pulsing sound that changes with speed, and so not the sound I am trying to diagnose. I also looked under the rear end from both sides of the wheel while spinning and the tires are not touching anything. There really isn’t anything they could touch.

The next steps were,

  • remove the tire
  • place a screwdriver so that it is almost touching the back of the rotor, but not quite touching
  • spin the rotor to make sure that there is no point where the rotor touches the tip of the screwdriver (meaning that the rotor is warped, etc)

The distance between the tip of the screwdriver and the rotor does not change meaning that the rotor is not warped.

The next steps were,

  • remove the brake caliper
  • remove the caliper bracket
  • remove the rotor
  • place a screwdriver so that it is almost touching the back of the hub, but not quite touching
  • spin the hub to make sure that there is no point where the rotor touches the tip of the screwdriver) meaning that the hub is mis-aligned/damaged

The distance between the tip of the screwdriver and the hub does not change meaning that the hub is not damaged. The hub spins very freely and straight.

The next steps were,

  • inspect the brake pads
  • inspect the rotor
  • inspect the caliper

The brake pads show very even wear as measured by a caliper (and also very little wear). The is no evidence of anything rubbing on the rotor or the inside of the tire. The caliper slide pins move easily and the is no evidence of anything leaking.

There was nothing left to do so I cleaned up the caliper, bracket, slippers, and pads with a wire brush wheel on a drill. I took the cap off of the brake fluid reservoir and used the caliper tool to screw the pistons back in. I re-greased the slide pins, slippers, and pad ears. I cleaned the rotor with brake fluid and put the brakes back together. I reinstalled the tires and torqued the lug nuts. I pumped the brake pedal back to firm.

Though I didn’t fix anything that I am aware of the sound seemed to be gone when I took it for a test drive. I still have no idea what the issue was. It did seem to be related to the brakes because it went away when I pressed on the pedal. The van was still moving, so the speed of the sound should have just slowed down and not disappeared. This is why I took the brakes apart but I still don’t know what I did to fix it.

I am going to service the front brakes as well as I like to do that once a year anyway. I will report if the sound comes back. The hubs, calipers, rotors, pads, and dust shields are relatively new so I wouldn’t expect to find problems.

Has anyone else seen anything like that?

LMHmedchem