I have a rear-end (seems like left side) vibration in my 2001 2wd that I'm having trouble diagnosing. Maybe one of you can help me. Here are the particulars:

- It's a low frequency rumble that sounds like something set into vibration by friction maybe
- It happens only between 45 mph and 55 mph
- It comes and goes, lasting from 1 second to maybe 3 seconds at-a-time
- It usually only happens when I first drive the car each day, for maybe 10 to 20 minutes and then I usually don't hear it the rest of the day, unless the car rests for more than 4 hours or so
- It happens in cold weather, hot weather, wet weather and dry weather
- The hub has very little, if any play in it

I recently replaced the left rear rotor. The inside surface was heavily grooved and had very little thickness left, while the outside looked nearly new. The inside pad was down to metal and the outside pad had about 1/4" left. I assumed that replacing those parts would remedy it, but no.

Any ideas?

Thanks a bunch

 

Also, I noticed the last couple of days that there is sometimes a "hoot" type sound when I'm at very slow speeds, such as in a parking lot. Sometimes it's long, sometimes it's short.

 

When the inboard pad wears faster than the outboard pad, the caliper piston is not releasing properly. There are 2 things that can cause this: 1) The caliper piston is binding in the bore of the caliper... replace the caliper. 2) The rubber flex hose is collapsed not allowing fluid to exit the caliper when you release the brakes... replace the flex hose.

The rear disc brake system on this vehicle is a great system, when it's maintained properly. Proper maintenance includes replacement of the pads, rotors, calipers, hardware and brackets with each brake service. In other words, when the pads wear out, replace all of it. If you don't, you'll have problems like you're experiencing right now

 

Thanks Captain - I really appreciate it. From what I can see, the line looks to be in good shape, so it's likely the caliper.

 

Looks can be deceiving: when/if the hose collapses, it happens on the inside and you can't tell just by looking at it It's far more common for the piston to bind.

 

Okay - so one of the slide pins was frozen. Since I'm short on cash at the moment and can't afford to replace everything, I've replaced the caliper bracket. The piston seems to be moving freely. I'm still getting the vibration.

One thing I noticed is that the new rotor is slightly burnished. Is it possible that it has warped? If so, who would I take it to to find out. The wheel turns freely, so I'm pretty sure the parking break isn't to blame.

 

If the rotor is showing signs of extreme heat, (burnishing) it's quite possible that's what's causing the vibration when braking. It would be best to replace it but an option is to resurface it. Some parts stores have brake lathes to resurface it but with the price of rotors, it's hardly worth it. Resurfacing will true it back up but, it will also weaken the rotor and increase the possibility of warping in the future.

EDIT: The frozen guide pins in the bracket will cause the outboard pads to wear faster, not the inboard pads. Flex line or caliper piston causes the inboard pad to wear faster

 

Have you checked your drive shaft u-joints?

 

Thanks guys - I really appreciate your input.

Actually, it has occurred to me that the vibration only happens when there is a load on the drive train. Never when slowing down or coasting. I think the brakes are in good shape now, so...

That's what I've been wondering lately, although I haven't noticed any clunking when putting it into gear. I'm wondering also if the differential might be dry or slipping.

The most mystifying aspects are that it only happens between 45 and 55 and usually only for the first bit of driving each day. The rest of the day it rarely, if ever, vibrates - which makes me think that once whatever it is is warmed up, it acts normal.

I did hear something on Car Talk that made me wonder if it could be the transmission lock-up. Any thoughts on that?

 

No sorry I don't. The reason I say u-joints is that my son's truck had a pretty good vibration at certain speeds on a '95 GMC 1/2 ton 4 x 4 and it turned out to be the rear u-joint. Replaced that fairly easily and it solved the problem totally.