Noise from the rear

[SharkPilot]

Yesterday on the way to work I started hearing a scraping noise from the rear. It had the same rythem as the wheel speed and almost sounded like something was caught up in there and rubbing against the tire. I heard it a couple of times and then it was quiet. Seven miles later after exiting the freeway it was back a couple more times.
On the way home it did it again and there was also a "clink" sound when I started moving. When I was close to home I opened the left side window and could plainly hear it on the outside too.
There was one intreresting clue... While it was making the noise on the freeway (about 35mph) I ran over a small road joint and the noise instantly stopped.
This morning I turned the car around to back it into the garage. Each time I changed direction I could hear that "clink" sound.
Pulled off the left rear wheel and found nothing unusual. I was thinking the hub bearing would be noticably loose or perhaps the axle shaft u-joints but they all look okay. The right side doesn't look any different. Both rear wheel bearings have similar play and I can't feel or see any movement in the u-joints. I have not looked at the driveshaft but this sounded like it was connected with wheel speed.
Oh, and the car has 40,000 miles on it.
You guys have seen (heard?) bearing failures before. Is that what this sounds like? I'm kind of puzzled since there is no smoking gun under there but I'm new to C4's so there is still a lot to learn.

As always, thanks for the help. SharkPilot.

[rhipsher]

Mmmm! The next thing I would check would be to see if maybe the drive shaft might be rubbing against the Cbeam. But I would also suspect a bad ujoint. You can't tell by just looking if one of the bearings are froze up on one. That can also cause ticking. When I replaced all of my ujoints one of the half shaft ujoint bearings was totally froze up and wouldn't turn anymore. But replacing them took care of any noise. But if you noticed a clink noise when turning the front wheels that usually means a bad ball joint from my experiance. Jack the front of the car up and put one hand on the top of the tire and the other hand on the bottom of the tire and move it side to side. If the wheel feels loose then ball joint. It may only have 40k on it but it's still 19 years old. Time will also cause failure on parts.

[jonszr1]

what was the amnt of play on the bearings?

[SharkPilot]

When the wheels were still on there might have been 1/8" or less play at the shoulder of the tire. Both sides felt the same.

I also checked and see no evidence of the driveshaft touching the C-beam. I would think that would be a rather ominous thing to find.

But if you noticed a clink noise when turning the front wheels that usually means a bad ball joint from my experiance.

The noise wasn't related to steering the front wheels. It happened when starting to move forward and reverse and seems very much to come from the rear. Left rear especially.

Right now I'm thinking u-joints. They are old and it's not a huge job to pull them out and at least check them out of the car where I could readily detect any stiffness or other issues.

[batchman]

Originally Posted by SharkPilot

When the wheels were still on there might have been 1/8" or less play at the shoulder of the tire. Both sides felt the same.

Those wheel bearings are shot. There should be no discernible play. The FSM allows for .005", which is not much at all. I wind up changing these once or twice a season on both my wife's and now this autocross car. PITA but there are no good alternatives, it's inherent in the design. Of course with our application we're um, a little harder on them than most folks LOL.

Todays' sticky DOT slicks are waaaay past anything that was imagined back when this design was penned.

Best,
- Jeff

[jonszr1]

have you thought about trying the new tapered bearing thats out . might help if you are hard on them

[rhipsher]

Then it might be U-joints. If visually inspecting them tells you nothing then jack up the rear end and put it on jack stands. Have a freind get in and turn the car on and put it in 1st gear. Slide under it on a creeper and you can really see whats going on there. Then have him put the breaks on and put it in reverse then you will be able to see and hear what it is. Its kinda scarry but I've had to do it.

[flyin ryan]

Friend of mine who doesn't come on here much, craigs427, has 95 AB Zee #103. He's a GM Tech. Last year he kept telling me he was hearing a noise going around corners from the rear end area...sometimes? I heard it a little bit, but not really bad/obvious. He just had the rear end out & we put some 4.10 'Viper' gears in it. Well a couple posi clutch plates were broken at the tabs & the clutch 'Clips' were laying in the bottom of the case. Fixed that, went for a drive about four hours ago, works killer & no noise. Not saying this is your problem...just saying .

[SharkPilot]

Interesting... thanks for the idea.

This noise happens going straight and mostly at low speed. Though as it got worse it was happening at progessively higher speeds. Considering how quickly it showed up and worsened, it was a little scary.
At first I thought it was something rattling inside the car because it sounded like it was coming from right behind me inside the car. That was the 'clink' sound. Then I heard the rubbing sound and also heard it echoing back at me from outside. I figured the cause would be real obvious when I started looking but I was incorrect.
I have heard of the hub bearings making some odd noises so that's why I was asking. I've never heard them myself. My Sharks have real greased bearings so they're different.

I like the idea of running it up in the air. Even though it will take some courage to roll under there and listen.

[ittlfly]

I had a similar problem on the left side. I found the clicking came from the worn out teflon washer (it is # 5 in the picture). When I replaced it no more clicking....although, I'm not saying it isn't a u joint. The clicking is a common problem with a lot of C-4's. The clunk does sound like a u joint going bad though. If you R&R it and still have the 'click', then change out the washer.