Hey guys, I always have turned to this site for knowledge and info regarding old chevys, but this will be the first time I have posted

My problem is this- before I left for college, I seemed to develop a fairly loud knocking sound coming from under the car anytime the wheels were in motion. It sounded like it originated anywhere from the transmission on back. I replaced the u joints, with no improvement.

Skip forward to yesterday- me and a buddy were trying to diagnose it yet again, and suspected it was coming from the rearend. We checked the fluid and it looked fine. We then lifted up the rear and ran the car in every gear. Sure enough the sound was barley audible over the exhaust, and even more so when we killed the engine and the wheels slowly rolled to a stop. However the sound was nonexistant when the brakes were applied and the wheels didnt move.

We determined that the sound was instead coming from the rear right wheel/drum, and we were able to reproduce the exact same sound when we pushed and pulled on the wheel itself. The wheel/drum has about a ~1-2mm play in it from the axle, and I wanted to clarify if a bad wheel bearing is the culprit for the loud knocking. It definetly doesnt look like the rear end/ujoint is the cause for the problem, it seems that this play between the axle and wheel is what is causing the sound. I have only driven the car since then to diagnose the problem , fearing that I might cause more damage to whatever was busted. Please advise me on what is up so I can get this thing drivable again!

thanks for any replies
scott

It's real simple to see if something is wrong with the bearings.
Just pull the rear end cover and pull the bolt that retains the pin that runs thru the carrier.
Then push the axle inward towards the center of the car and pull the C-clip off. Then you will be able to pull the axle out.
Look for damage to the bearing surface on the axle.
Use a flashlight to look at the bearing in the axle tube.
let us know what you find.
You'll need a new gasket and some new gear oil to get it back together. Or you can use a good silicone sealer in place of the gasket.

btw, it's normal to have end play with the axle. You'll see why when you pull the cover. It's the space between the axle end and the pin that retains the side gears.


Nate

Scott,
Does the knocking sound occur when going down hill and letting up on the gas?

I had a knock like that and it turned out to be the brake shoes rattling.
New brake hardware kits took care of it.

Nate- I was unaware that it was normal to have some play in the axle, but it still seems odd to me that by moving the wheel back and forth into the axle that it should produce the same sound we are looking to try and fix. I wont be able to get back under there until i get the parts, so hopefully I'll let you guys know what I find.

Dean- Yea, the sound occurs pretty much whenever the wheels are in motion. It happens in park, 1-3rd gears and neutral, and at first listen seem to come from the tranny, but when we put the rear end up in the air and put it in drive, it was evident the sound was more rear-oriented.

Hopefully this is just a wheel bearing, but what are other possibilites? Thanks for the replies so far guys

Ok, tried some more troubleshooting with my uncle this time- we both finally agreed that the amount of play in the wheels/axle was fine, but when we took off the suspect wheel, we both noticed that when we rotated the axle by hand, there is a distinctive "graveliness" and a faint clunk and rough spot when the axle hit a certain point along it's rotation. SO now I am fearing the worse- that the rearend might be damaged. It almost seems like the gears in the diff are skipping a tooth, and the roughness of turning the axle by hand is some metal debris. Havnt actaully lloked in the diff cover though. But what do you guys think? Busted rear end, or somehting else?

Meatstone...I have the same noise and have diagnosed (attempted to anyway)the same way you and others suggest. Please post your findings when you get them so I know where to look for answers. I will do the same when I find out anything. I am going to a rear end specialist soon so he can check the noise out.

Just a note, if you have a 12bolt make sure you use a new rear gasket cover instead of silicone, there is a trail in the rearend cover that lubes stuff, if you use silicone the lube wont travel in the groove and it can fry stuff after a while

take the cover off,if there is metal in the rear end oil, you need to disassemble and clean everything, I'm sure you'll find the reason for the noise easily.

Meatstone, try jacking up the rear end by the pumpkin, add jackstands, block the front wheels then putting the car in drive. While the wheels are turning, pull on the e brake cable on the suspect side (where the cable is exposed from the sheathing). Listen to see if there is any change in the pitch of the noise that you're experiencing. By putting a load on the axle, you change the "freewheeling" sound to something closer to what you would hear on the road. I've always used this method in the past to diagnose bad axle bearings and it usually proves correct.

What's keeping you from taking the cover off and having a look ???
Outer wheel bearings are not hard to replace.

Nate