Hi guys, looking for a little guidance tracking down a rear end noise. Any help/direction is appreciated.
This car is 79 corvette with 13K miles. My dad bought this car back in 84 with 10K, drove it a few years and parked it. I’m trying to bring this car back to life.
I get the car on a lift for an initial inspection. The rear diff was very wet. Both side yokes and the front pinion appeared to be leaking. I pulled out the diff and had a local shop here in Illinois reseal it and go through and make sure there’s nothing wrong. Diff gets a good bill of health, new seals, new crush sleeve, bearings and clutches although original looked good. While the diff was out for service I get the car up and running, new fluids, and tune up work. I also replaced all 6 u joints.

Once the diff is back in the car I take it for an initial drive. I have what I would call a rrrrr rrrrr rrrrr noise coming from the back. The noise appears to be related to wheel speed. Not 3 times faster as if the pinion had an issue.

The noise speeds up when wheel speed increases. I don’t hear the noise going around R or L hand corners.
2 bottles of posi lube and 80/90 lube for the rest. Braking has no effect on the noise. The noise starts at about 25mph. And as a precaution I replaced the front wheel bearings as well.

With the car on the lift, support the trailing arms as if it's sitting on the ground, I let the wheels spin to see if I can hear the noise thru a screw driver. No noise whatsoever. Not sure if there needs to be directional resistance (rolling) in order for the noise to appear, but I can't hear a darn thing.

I take the car up to the shop that did the diff, they say the noise is in the wheel bearings. Back home, up on the lift, pull the trailing arms, send them out for rebuild. Re-installed. Same noise…. Ugh…. Is there some test I can do to definitively point to Diff or wheel bearings? I have the trailing arm guy pointing to the diff, I got the diff guy pointing to the trailing arm guy.

My gut says its the Diff since the noise was there before and after but I have nothing to back it up with since I can’t hear it on the lift.

What do you guys think?

 

Bottom line, I can't hear it at all.
A few friends that are Corvette enthusiasts? Local Corvette club? Meet some Corvette enthusiasts at car shows?
Get someone with some experience to ride along.
Your description doesn't say where the noise is coming from. A tire rubbing? I don't know, can't hear it.

 

hmm,
wild *** guess, diff bearing.

 

Sounds like you are shooting in the dark and so are your guys. It's ok for you since you're paying someone for the work. Grab a wheel stud, can you feel it move when you push or pull on it. Does anything look like it might be rubbing?

13k miles is low however the age of the grease in the outer bearings would be a concern and if the car sat a long time over a moisture area the bearings can seize on the shaft or to the races. Now this should have been picked up but any competent shop rebuilding TA.

The differential had oil leaks, possibly the bearings were still good, but they could have been bad from sitting. There should be no noise within the diff if all new bearings were installed and the diff setup correctly. How much endplay are in the diff axles? Were the pinion splines sealed and if so with what? If you don't know and your guy doesn't or used the wrong stuff it most certainly will be leaking again.

How old are the tires? how about alignment, rubber bushings dry rot over 45 years.

 

Unfortunately we have poor quality control - so don't count out that new parts as good. That's from experience. A little leery of store branded parts. with the exception of NAPA

 

GTR - Definitely shooting in the dark right now. Appreciate your reply. I read many of your post before.
I don't see any rubbing anywhere, tires or halfshafts.
The age of the grease in the wheel bearings was my concern as well. One of the reason I had the TA's rebuilt as well as it might have been the source or my noise.
Forgot to mention the tires are brand new. I even rotated them the other day to see if it helped.
Rear alignment is out. I know that. I was trying not to spend the money on an alignment only to rip everything apart again to correct the noise (once it's identified). It's not like it's way out tough. The car tracks pretty well.
So far no leaks from Diff, I do not know axles endplay though.
When you say grab a wheel stud, are you saying grab the wheel while it's off the ground and then push and pull?

 

With the wheel off the car, grab a wheel stud and see if you can see and feel the axle move in/out. It will give you an indication of the level of work that was done. Rear bearings are not special other than the fact they have to be a press fit correctly setup. The bearings are not high precision, expensive machinery bearings. You can buy TA rebuild all over the place and they all vary in quality from very good to let's say questionable. Point being, even setup loose within the spec, they will work somewhat but should not be causing noise.

Now with that said, I lost track on how many diff's, boxes, and TA were sent to me over the years to repair previous work from vette shops, local garage, online purchased units, they all had one thing in common- lousy work and built to sell cheap. I can't say this is what you're dealing with since I have not inspected them but if you can see and feel the axle moving by hand there is more than 003" endplay in the bearings. The cheap guys rebuilding these use the cheapest bearings they can find; I recall one customer who supplied his rebuilder with new USA Timken and later brought me the arms to fix. The bearings were all no name imported ones, no Timken's to be found. This from a trusted local garage that "knows Corvettes". Any simpleton on the street probably knows a corvette but do you want them to work on your car? Again, not saying that is what you have going on, but I have seen it countless times.

The same goes for the differential. I have pictures dating back decades of bad work, it's not new it actually worse today than ever before. Partly because of greed and also because those who know these old cars are retiring or dying and what taking their place is not impressive. This is a general statement, not directed at any particular person or place.

It is hard to pinpoint your issue, if there is an issue, without inspection. If you didn't take any pictures of the diff before and after, there's not much I can base any judgement on, sorry to say.

 

Dust shields rubbing? E brake dragging inside of hub?

 

GTR I'll give that a try. I'm out of town for work right now but will get on that as soon as I get back.'

Mr E. It's not a scraping noise and it's not that tin kinda sound. Appreciate the thought though.

 

GTR: Ok, back in town. Took the wheel off and setup a dial indicator on the rotor hat. It's tight, only .001 of movement. Should I have the caliper and pads on for this test?

Appreciate the help.

 

I would replace the wheel bearings due to the no noise when you turn the car. Since it sat for a long time maybe the bearings are damaged or corroded. Wheel bearings shouldn't be very expensive, so I think replacing them is a good idea any way you look at it. Good luck.

 

It might be better to have a conversation over the phone. If you want PM your number and I will call you.

 

Sent.

 

Have you tried 'listening' to the pinion and side bearings with it elevated? I would suggest a long wood stick/broomhandle/dowel/etc that's longer (so you're away from rotating elements). Longer works just as well.

Also, this probably isn't it, but did you 'stress-relieve' the u-joints after you installed them? (counter-tapped so the trunions aren't tightly pre-loaded). Someone suggested emergency brakes...double check that for sure. Loosen them up real well for testing purposes. Are your rotors 'true'? The caliper pistons are spring-loaded and IDK what kind of noise that might make. If the rotors are not super-true the umbrella-style seals (known as 'Lip' seals) will pump air back into the brakes, e.g. like a jellyfish moves. It's harder to get a reading on the rear rotors with a dial indicator, but I'd sure do a check. Esp if you end up with the axles unhooked.

I guess before spending any more money, if it were my car, I'd listen to the other bearings again..see if you hear anything now that you may have missed before. Then maybe unhook the driveshafts and rotate the rear spindles by hand..just to 'see'. And rotate the pinion by hand too (no side shafts)...if you happen to have them and the d/s off. Sometimes you can 'feel' things by hand. Do the side-shafts move in/out at all? (not the T/A's). Is there much/any up/down play in the transmission output bushing? Shouldn't be with the low miles your car has. There could be things like a cracked outer diff race and things like that. Dodge Ram had a recall not that long ago on 1500 pickups which developed a persistent wa-wa noise due to a batch of rear diffs which had cracked outer race during assembly. A hairline crack. You could look that up and see if the sound matches what you're experiencing. I'm sure there are y/t videos on it. Not saying that's your issue, but if all else fails, it might be worth a look. You could do that on your own. Diff's aren't that difficult to do. If you take yours apart, just keep the shims separate. There's a lot of Y/T videos on the subject. I've done a few car/truck (non vette) ones.

Back to the rotors... as you know, GM riveted the rotors to 'un-true' spindle hub flanges...and THEN turned the rotors (on the untrue hubs). That made the rotors true, regardless of hub flange specs. But if anyone has drilled out & replaced the rotors its likely you're running with new rotors on 'untrue' hub flanges which equals untrue rotors ..which also equals wobbly tires! You'll have to tighten the front spindle nut a little to get a good D/I reading (and reset afterwards). To give you an idea of what that can mean is, on mine, the hub faces were off .005" which translated into about .013 at the outer rotor area. (they should be .002 or less!). And also.... something sometimes overlooked is, some brand new rotors are machined with a 'radius' inside the hub flange mating face (inside the rotor). It's a little detail that can have big consequences. The GM design is the inner angle of the rotor should be "square-cut". If someone were to install a rotor that has a rounded inner cut, it will mount wonky ...IT WON'T FIT PROPERLY. I just typed that in caps to emphasize. You can't see it. But they end up fitting wonky so it'll mimic badly warped rotors. And if the rotor face is off by a fair amount (front or rear) ....the wheel/tire will be wobbling quite a bit going down the road and that could produce a noise. Tire run-out could be as much as 5/16" of an inch! And that could produce a wa-wa noise as the whole assembly moves the spindle in/out. I put the following drawing of a rotor and hub face together below to illustrate what I mean. And if you have the rear rotors off, and esp if the rear axle shafts are unhooked, check the rear spindle flange face with a D/I to make sure they're 'true' too. Mount a wheel and spin it freely and see that it's spinning 'true'. I bought 6 used Corvette AL wheels from a couple different internet sellers that look pretty decent, and guess what? They're all warped! And not just a little. More than i want to run. Pretty sure the sellers had no idea. Corvettes tend to get rough-housed...and wheels in my case got warped. As far as tires go, if you wanted/needed, you could have them verified on a Hunter Road Force Balancer. I'm thinking out loud here but details matter in a job like this ...sorry for the rambling..

So there's still some things to check out. Good luck. Let us know what it turns out to be.