Gear change and rear end noise.

[bhedberg]

After having 4.10 gears swapped into a 1990, I am experiencing a very loud low frequency hum at highway speeds, the faster the louder. I got the gears from Al Kindler years ago. The build replaced all the seals and bearings and was performed by ctaxleservice.com in Ellington CT. The loud hum is so persistent as to make a long highway trip something not to look forward to. The noise does not appear to be related to anything except how fast the wheels are turning. It is the same regardless of the gear you are in, whether accelerating or decelerating, or just coasting. I suspect there is some issue with the setting up of the gears but I am not sure. Is it possible a wheel bearing could do that? Also, I am not sure I got the half shafts in the same orientation with respect to the yokes or not. Could something like that be related? Does anyone know who I should be looking for to have the problem properly evaluated and diagnosed? I hear people talk about gear whine or clunks etc from differentials, but have found nothing similar to what this car is doing. It is a lot of work pulling the diff, I'd hate to do it again and still not get it resolved. I am reluctant to take it back to the fellow that did the work because I am most interested in getting it fixed rather than having a battle. Any suggestions appreciated.

[Paul Workman]

Bill,
When I changed U-joints (drive shaft) I had "hum" like you describe. But, when I pulled the shaft out and reinstalled it 180º relative to the differential yoke, all was well again.

I would guess the drive shaft balance before being concerned about the half-shafts: they turn MUCH slower than the drive shaft. AND, after installing 4:10s, the drive shaft out of balance would be exacerbated due to the higher rpm/mph!

You might have to take it to a driveline shop to verify everything is OK. But, as for the setup of the ring/pinion gears...I guess you'll have a better idea after the drive/half shafts have been taken out of the picture. (Usually, there is a lot of gear howl if the ring/pinion have not been properly set up - or at least that has been my experience.

Hope this helps.

P.

[Hib Halverson]

What you do next kinda depends on how much work you want to do.

One choice would be to take the car to another rear axle service facility and either give them a ride or let them test drive the car then ask their opinion.

Another would be to buy yourself an automotive stethoscope, get the car up in the air and support it by the rear knuckles so the half-shaft angle is not too severed then have an assistant run the car in 3rd or 4th gear with you listening to the axle and/or the trailing arm bearings so see the specific source of the noise, ie: pinion bearings, side bearings and so forth.

Be careful of that hot exhaust.

The last choice would be, if you have access to "Picoscope" equipment, which is what GM dealers use to diagnose noise complaints, and that will quickly pinpoint the noise problem.

I'd say you have a 90% change the problem is in the axle and 10% something else.

A prop shaft balance problem will make a buzzing vibration you can feel and in some cases hear.

Finally, there are a few just plain "bad" gearsets out there which make noise and cannot be fixed by gear set-up.

Whatever it is, if the hum is that loud, it's going to be something major and quite obvious.

[32valvZ]

Originally Posted by bhedberg

After having 4.10 gears swapped into a 1990, I am experiencing a very loud low frequency hum at highway speeds, the faster the louder. I got the gears from Al Kindler years ago. The build replaced all the seals and bearings and was performed by ctaxleservice.com in Ellington CT. The loud hum is so persistent as to make a long highway trip something not to look forward to. The noise does not appear to be related to anything except how fast the wheels are turning. It is the same regardless of the gear you are in, whether accelerating or decelerating, or just coasting. I suspect there is some issue with the setting up of the gears but I am not sure. Is it possible a wheel bearing could do that? Also, I am not sure I got the half shafts in the same orientation with respect to the yokes or not. Could something like that be related? Does anyone know who I should be looking for to have the problem properly evaluated and diagnosed? I hear people talk about gear whine or clunks etc from differentials, but have found nothing similar to what this car is doing. It is a lot of work pulling the diff, I'd hate to do it again and still not get it resolved. I am reluctant to take it back to the fellow that did the work because I am most interested in getting it fixed rather than having a battle. Any suggestions appreciated.

In my opinion, that points more to a bearing, hard to say which, but since it appeared after the swap, Id be inclined to think either carrier or pinion bearing more so than wheel bearing...

[BYEBYE2U]

Hope the gears are not RICHMOND Gears
Notorious for noise ....no matter how well set up
3 out of 4 sets i have installed made noise
Accelerating n trailing noise still there ?
Try trailing arms n stethoscope as an easy start 1st

[bhedberg]

I think my next step will be to reorient the drive shaft as Paul mentioned. That is just 4 bolts out and back in again. If that is not the end of the story I guess I'll try to find a shop that hopefully has somebody that can quickly pinpoint the problem. If it is drive shaft balance it seems to explain the symptoms better than a problem with the gear change. Thanks for the input.

[bhedberg]

I just got back from my test drive after rotating the drive shaft 180 degrees at the differential yoke. Low and behold problem solved. No more loud low freq hum at speed. Thanks to Paul Workman who identified the solution and also to all that provided input. I had no idea that imbalance in that shaft could manifest itself in that way.

[Hib Halverson]

Originally Posted by Hib Halverson

(snip)Whatever it is, if the hum is that loud, it's going to be something major and quite obvious.

Ok.
I get to eat crow on this one.

Originally Posted by Paul Workman

Bill,
When I changed U-joints (drive shaft) I had "hum" like you describe. But, when I pulled the shaft out and reinstalled it 180º relative to the differential yoke, all was well again.(snip)

...and Paul gets a Saturday morning Beacon of Reality Award