Hi, I just replaced the pinion seal on my 82 Z28. No more leaks, but now I have a very slight whining noise when going 30+ mph with just a light touch of the accelerator. Just rolling down the road with no gas applied - no noise. Anything more than just slight gas (foot basically resting on pedal) - no noise. Not loud at all. I was very careful when I took the pinion nut off to mark it, count the threads, and put it back on exactly the same way. Could a slight noise like this be due to incorrect backlash? Perhaps I tightened it too much? I did not torque it super tight. I've only driven it 20 miles or so since replacing the seal. Not a posi. Thanks

 

You didn't change backlash at all. Most you could have done was change bearing preload on the pinion bearings. How did you mark the pinion nut? Did you check rotational force before and after?

 

Marked with paint and I did not check rotational force. Maybe its too tight?

 

Could you be 1 thread too loose? That would be a problem.
If you went too tight, you would have had to turn that nut with 250+ ft/lbs of torque to crush the crush sleeve further.
That would be a giant breaker bar with an additional 4 foot piece of pipe and all your body weight pulling on it to do so.

 

So if anything, I should try tightening it a bit to see if the noise goes away?

Forgot to mention that the pinion seal was leaking when I got the car. When I changed out the fluid and filled it up, it started leaking out of the seal so I went back in and changed the seal. I have no idea how many miles the car was driven with the fluid down to below the seal. So this differential could have been low on fluid for quite a while. I did not notice any noise before I touched it, either to replace the fluid or replace the seal. So I don't think I should have any noise (however slight) now. I can live with it, but want to make sure I'm not damaging anything. I have a feeling the nut is not tightened correctly. So a loose nut could cause a noise like this but not one a bit tighter than what it was before?

Thanks for all your input. This forum is a lifesaver.

 

I would start here. As NoEmissions said it will take some serious torque to crush the crush sleeve more, so if you can tighten it more run it up to where you can’t tighten it with any ease, say a 1/2” drive ratchet. Then check the rotational drag and see if it seems good. Then road check it again hopefully that cures your problem

 

 

It's REALLY hard to tell anything about rotational torque in a fully assembled rear axle. Not impossible; but not a high-probability task for a novice.

I'd suggest just tightening the nut A LITTLE. The reason it was loose in the first place, was because the bearings are worn. All you need is a few .001"s, to take up the wear. I'd suggest something like ½ of one flat of the nut; 1/12 of a turn. 30°. You should find that the torque on the nut remains somewhat constant for a bit, then DRAMATICALLY increases after that. The increase is due to further crushment of the crush sleeve. That's what you're looking for: you want to crush it A LITTLE BIT (sorry for the technical term: a very precisely measured quantity there) more, but not TOO MUCH (equally precise and technical). Always remember though, once the crush sleeve is crushed, it DOES NOT spring back. Therefore you want to go A LITTLE BIT at a time until EITHER you're satisfied, or until it gets worse... if you're satisfied then it's all good, but if it gets worse, that means the bearings are too far gone to just adjust out the free play. You MUST avoid getting too greedy all at once.

 

The previous posters have good advice. The issue is that your contact pattern is off very slightly and the gears are either tip or heel loaded at very light torque load as you move from lash to light contact. As you add torque, there is a little flex in the components and the contact pattern shifts, evens out, and the noise goes away as the entire tooth takes the load. If you can't fix it with a slight adjustment to the nut, I wouldn't worry. I can't guarantee anything, but in my experience it should not hurt anything. I had a car and a Suburban that did this for years at light torque and certain road speeds. Sometimes the system will actually be stronger at full torque with a little noise at light load. The gear engineers work very hard to keep the pattern centered across the full range of torque, but it is very difficult to achieve.

 

Tightened pinion nut up a bit (30 degrees or so) and noise is no better or worse, so that wasn't it. I attached a sound clip of it where I coasted and then lightly touched the gas to make the sound, then let off the gas. Did this 5-6 times. I can hear it in the audio, although it's faint. I may have to learn to live with it at least until the rear end disintegrates. It was low on fluid (down to the low edge of the pinion seal) for an unknown amount of miles so there may be some damage done.

 

Just curious , do you have tubular rear control arms and panhard bar , maybe with poly bushings ? I ask because the bushings in my factory parts went bad and I installed the aftermarket tubular parts , and every sound the rear end makes is now broadcast through the car quite loudly .

 

That's bearings. If the noise didn't change then they're probably just worn, and you can either change them out, or turn the radio up a bit.

Incidentally, the formal words for the 3 possible states of the rear end are "drive" (engine pushing the car), "coast" (car pulling the engine), and "float" (no torque in either direction. Your description sounds like you have noise in "float".

 

The Chevy shop manual for my '85 instructs to mark the pinion shaft, flange, and nut on disassembly (which you did). On reassembly, it says to tighten 1/16 of an inch past the original marks. So I wouldn't go any further than you already have or you'll apply too much preload to the bearings. It sounds as if you have classic gear whine due to the pattern being off center a little. It may be due to bearing wear, or it was always there and something changed in your suspension and bushings that is causing it to be transmitted into the cabin. Noise is either airborne or it has a mechanical path into the car (or a combination). If you changed anything else lately that could cause a "ground out" or stiffness change of suspension arms, shocks, parking brake cables, exhaust, etc, it could be providing a better transmission path into the car. If the noise stays as a light whine on light acceleration, it shouldn't be harmful. If it changes to a more constant growling / howling noise, then I would be concerned about a bearing failure approaching.

 

I'm going with the turn the radio up option. I put a really nice system in there for a reason - to drown out all the ratttles, squeaks, and whining noises. I'm sure it will let me know when it's ready to come apart, then I can swap out with another rear end. Thanks

 

Here is the way I see this:
Suppose he is actually 1 turn loose.
He would never know that because the ring gear is still there and the previous backlash was something like .010".
Now he assumes the nut is back where it belongs, but it's actually loose - which means ZERO backlash and no pinion gear preload as he is driving down the road.
Are my assumptions correct?

steveusaf - how hard was it to turn that pinion nut the additional 30 degrees? To crush that sleeve further, it takes 2 men + 1 boy.

I got that same noise in float when my ring gear bolts loosened up which caused the backlash to go to zero (I didn't use RED Loctite).

The only way you will know for sure is to pop the cover off, loosen the caps (don't remove the bolts because you do not want the entire differential to pop out - along with the side shims falling to the ground and getting mixed up), pry the diff away from the pinion gear a small amount, and then see if you can wiggle the pinion back-and-forth in the case. If so, then you are certainly too loose.

 

Tightening the nut doesn't really change the backlash. Once the nut is tight enough to take up all the bearing play, the pinion is SOLID up against the shim, and no matter how tight the nut, that doesn't change. Unless the head bearing is SO worn that the pinion can pull out (hehehehe) enough to affect it. Loose is a different matter; that will let the pinion get sucked into the housing in coast and float.

But yeah, loose carrier bearings will make noise, as well as loose (or worn) pinion ones. And they all tend to loosen up at the same times for the same reasons, like, running dry. Or water in the fluid. Or excessive heat. (*cough* exhaust that ends right in front of the axle *cough*)