Help with weird rear wheel noise

[chevyaddict]

I've been searching the threads but I don't feel confident enough in what I read so I thought I'd pose the question. This is on the 90. When driving it honestly sounded like a rear brake metal-to-metal sound when I was going down the road but the brakes are fine. I thought maybe something came lose (like a cable) and was hitting the inside rim or something but that isn't it. But it is definitely a grinding/clinking sound that happens with regularity upon the wheel turning - not all the time... on every revolution. I just now jacked up both rear tires, put the car in neutral, and as I slowly turn the tire (rear driver's side), there is a awful sounding "clink"; kinda sounds like something is in a bind momentarily and then works itself out. The rear u-joints look perfect. No obvious movement from them (I realize that doesn't mean they aren't bad) but usually you can visibly see a shift in the u-joint when you are turning it slowly that clues you in to it being bad. It doesn't clunk like that. It sounds like something is in a bind. Is this the dreaded rear wheel hub assembly going bad? How do I know for sure? The car has 121K miles on it.

 

[Huskerman]

Is the noise coming from the brake hub area or deeper inside like in the rear end.....?

 

[chevyaddict]

Definitely seems to be coming from the hub area. I tried to do the "bearing test" but absolutely nothing seems lose whatsoever, no matter which way I try to jiggle the assembly. But I did notice some fresh oil around the rear differential.... am wondering if my rear end is low in fluid so I plan on checking that.

 

[John Robinson]

If the diff is low on oil then you might be hearing the positraction. Since you can hear the noise with the car on jack stands and turning the wheel you could have someone turn the wheel while you use a length of rubber hose to listen for the noise. That way you should be able to isolate the area were the sound is coming from. Good luck finding what it is.

 

[Hib Halverson]

Has the rear axle lubricant ever been changed?

 

[chevyaddict]

Doubtful.... I got the car with 80K on it; it has 121K now.... I guess I should probably do this regardless, eh?

 

[Hib Halverson]

Doubtful.... I got the car with 80K on it; it has 121K now.... I guess I should probably do this regardless, eh?

Yep.
Only problem is C4 drive axles do not have drain plugs so you either have to install one or siphon the old lubricant out. Once you get the old lube out, I'd use the GL5 gear lubricant of your choice along with some friction modifier then road test to see if the "binding" noise you have been experiencing is gone.

 

[chevyaddict]

By friction modifier you mean the posi-traction extra lube, correct? I put some of that in there along with the good gear oil if I recall correctly, right? I did this quite awhile ago when I rebuilt my 81 rear end.

 

[Hib Halverson]

By friction modifier you mean the posi-traction extra lube, correct? I put some of that in there along with the good gear oil if I recall correctly, right? I did this quite awhile ago when I rebuilt my 81 rear end.

Friction modifier is AKA "limited slip additive" or "posi-traction additive" and, yes, it goes in with the gear oil.

Is the transmission in this car an automatic or a manual?

 

[chevyaddict]

Is the transmission in this car an automatic or a manual?

Automatic.

 

[ltmax]

Screatchy Rear

Does the car feel like it's fighting itself when your off the brake and just starting off, light on throttle? Is that noise really scratchy / screatchy? Definitely inspect your wheel bearings as much as you can.
I had a '69 427 and when that rear bearing let go after a long highway ride, it was wild scratchy and the back end would 'sink down' as I let the clutch out to take off. I'd mash the clutch again and the back would 'relax'. It took me 8 hours at the Air Force base hobby shop when I replaced the bearing - in shreds.... what an experience!
The guys have good ideas about the rear diff too. Check it all, let us know whahappened >>>>

 

[chevyaddict]

Does the car feel like it's fighting itself when your off the brake and just starting off, light on throttle? Is that noise really scratchy / screatchy? Definitely inspect your wheel bearings as much as you can.
I had a '69 427 and when that rear bearing let go after a long highway ride, it was wild scratchy and the back end would 'sink down' as I let the clutch out to take off. I'd mash the clutch again and the back would 'relax'. It took me 8 hours at the Air Force base hobby shop when I replaced the bearing - in shreds.... what an experience!
The guys have good ideas about the rear diff too. Check it all, let us know whahappened >>>>

Nope, none of that. Car rides perfectly. I wouldn't have even known anything was wrong if I didn't happen to hear it one night as I decided to turn my stereo off!!!

 

[bb2kksy]

Broken emergency break springs ?

 

[Hib Halverson]

Ok, if it's an automatic, it's got a D36 axle and the instructions I have to install a drain plug only apply to the D44.

Best bet is to get siphon tool, siphon out the old axle lube, fill it with cheap GL5 gear lube, drive it 10 miles, siphon out all that, then put in the good stuff with bottle of GM limited slip additive. Then, drive the car 10 miles on the highway to warm the new lube. After that find an empty parking lot and drive in slow tight circles. While doing that if you feel chatter or hear loud squealing from the rear axle, the limited slip is likely shot. If you don't hear anything, changing the lube was a good thing.

Now...in re-reading the OP, I'm thinking your hear this noise driving in a straight line. If that's the case, it likely is not the differential, but, that said...with 121,000 miles on the car and no known history of rear axle service, you still need to change that lube.

 

[John Robinson]

I found a large siphon tool at Harbor Freight. It looks like a big turkey baster. You will need some hose to fit on it and go into the diff to get out the fluid in there. Be sure to buy at least 2 feet of hose for the baster.

 

[chevyaddict]

Thanks for the baster note... there are always cool funky things at Harbor Freight. Hal, I should absolutely change the gear oil so I will do that but I don't think its coming from the rear end. It definitely sounds to me like it is around the hub area. This is why I thought it was the breaks at first. I'm hoping it is just a bad u-joint... and not the bearings! I'll get back underneath it next week start taking some things a part to see if I can identify it further. I'll let everyone know what I find!

 

[89Z51]

Noises...

Thanks for the baster note... there are always cool funky things at Harbor Freight. Hal, I should absolutely change the gear oil so I will do that but I don't think its coming from the rear end. It definitely sounds to me like it is around the hub area. This is why I thought it was the breaks at first. I'm hoping it is just a bad u-joint... and not the bearings! I'll get back underneath it next week start taking some things a part to see if I can identify it further. I'll let everyone know what I find!

I read your description at the beginning, sounds much like the typical "dry u-joint" sound. But, I will mention that I've had a bearing hub fail in such a way that there was a rough "spot" in it. It would make noise while driving (sounded different turning left vs. right), but the bearing still felt "tight" when I jacked the vehicle up and rotated the wheel - until I hit just the right spot. Suddenly there was obvious play. So, don't discount the possibility of a hub. On a more positive note (or maybe not) I'll suggest that the worst part of changing a bearing hub is getting the half-shaft out of the vehicle in the first place - which will need to be done anyway if it ends up being a u-joint.

 

[WhalePirot]

Be a great idea to replace the U-joints concurrently with the half-shaft removal. Also, don't go cheap on replacement bearings. Even the so-called top brand bearings can arrive, new-in-box with excessive play. That search is NOT fun as you may read.

I believe it is NOT recommended to run the rearwheels with the engine/driveline while jacked up.

 

[Hib Halverson]

You can as long as you also support the T-arms with stands so the u-joint angles are not extreme.

 

[chevyaddict]

Finally got a chance to get into this today. Took the car out - idled down the road with my driver's door open. Sound is completely independent of the brakes and doesn't change if I zig zag left to right. Sounds like metal on metal along with some "crinking" over and over. So, jacked it up, with the suspension supported on both sides, put her in neutral and hand-turned. Its not the u-joint, pretty sure. Every two rotations or so there is a loud "correction" sound as if something has gotten in a bind and then frees. No free-play in the bearings though. I feel pretty confident its the rear hub assembly. So, doesn't seem too hard to get it out, according to the manual, but I was reading before on other threads that one has to be careful. I also think someone said to ONLY replace them with Timken hubs and nothing else, is that correct? I see them on Ecklers for $220. Does anyone happen to know the size of the nut on the outside? It appears metric on mine and is in between a 1 and 3/8 inch and 1 and 7/16 inch. I'm assuming when I get the hub out it will be obvious if that is it or not.