Rear end Noise

tedh1 · November 3, 2002

Going to the stealer next week to have rear end noise looked at. Truck has made this noise from Day 1. Have 11,000 now. There is a high pitched noise that seems to be coming from the rear end when decelerating from highway speeed 50-65 MPH or above. When foot is taken completely off the pedal the noise can be heard even above the radio set at a moderate volume. As soon as foot is applied to accelerate, noise stops. Noise goes away when Allison downshifts below approx. 40 MPH. Noise will also go away if tranny shifted to neutral. This is a high pitched singing or whistling type noise. I suspect that rear end was set up wrong from factory, to much backlash or bad pinion bearing preload. Any ideas? I really don't want the rear end operated on internally be dealer. Should I try for a new rear end? I welcome anyone's thoughts on this one. Thanks!

SoMnDMAX · November 3, 2002

You're on the right track. Most likely the gearset was set up incorrectly, or the gears were machined incorrectly.

The dealer should be able to get a new gearset setup properly. Getting a whole new differential assembly may be a hard sell.

Shaners · November 4, 2002

A guy at work had the identical symptons on his 1500HD. The backlash was too tight (I think). His original dealer messed it up pretty bad when they tried to fix it. He took it to another dealer the second time and they fixed it right by replacing the gear set and by properly setting the backlash.

Good Luck

Kansas Kid · November 4, 2002

I would have to agree with the others in that you are on the right track. AAM seems to have a good bit of quality control problems....

MarkD · November 4, 2002

The general consensus around here is that once a gearset is noisy, it will be nearly impossible to correct. $200 worth of gears can save hours of disnosis/adjustment time.

BDBWTE · November 4, 2002

I've never heard of any toubles with AAM but that's just me..as far as your rear-end goes I would definately check the backlash and the pre-load on the rear end I've heard of them losing the pre-load in the rear-ends before...mostly Fords though..

Dihappy · November 4, 2002

Yup, sounds like the setup was goofed.

That and or the lack of GM Friction Additive.

SoMnDMAX · November 4, 2002

That and or the lack of GM Friction Additive.

GM friction additive is not necessary nor recommended in the AAM 11.5" differentials used in the 2500HD/3500's, regardless if the G80 locker is installed or not.

NJMax · November 5, 2002

Thanks to all that replied. I dread letting a dealer work on setting up new gears but with warranty work, I guess there is no choice. I'll post what I find out Wed. at the dealer. Thanks again.

Dihappy · November 5, 2002

That and or the lack of GM Friction Additive.

GM friction additive is not necessary nor recommended in the AAM 11.5" differentials used in the 2500HD/3500's, regardless if the G80 locker is installed or not.

Doh! IT is a 2500 aint it

tedh1 · November 7, 2002

Went to Maguires Chevrolet in Bordentown, N.J. yesterday. Technician said he knew what the problem was before we even went for the test drive. Seems that AAM doesn't do too good a job with the rear ends they furnish for GM trucks. They just pump them out and don't take time to set them up right. Tech says that they have to try adjustment first, i. e. take it apart and set it up using a new shim pack. Says they have done bunches of rear ends because of AAM's competence with no comebacks. I asked "What about the present wear pattern." He replied that he wouldn't know about that until he got in there. Seems to me that establishing a new wear pattern over an existing one is not the way to go. Any comments or suggestions? Taking it in next week.

SoMnDMAX · November 7, 2002

Though it's not the best way, resetting a gear set can be done. I've done it myself in 10 and 12 bolt Chevs, and 9" Fords, and have had zero failures. Just make sure everything is documented, just in case something does go wrong. Chances of success are quite high, since the gearset has relatively low mileage.

It'll be fine, IMHO.

tedh1 · November 21, 2002

Got my truck back yesterday from the dealer. Backlash was found to be too tight. Mechanic set it up to specs, test drove it and found that the noise is still present but reduced. When I picked it up, the service manager told me that they drove a new Duramax off the lot and it didn't make any noise. However when they called Chev technical assistance about my truck they were told that the noise was "normal" for a Duramax. I tried to explain to him that the truck could have a Volkswagen engine and that would have nothing to do with the rear end making noise. He then tried to tell me that the Duramax rear ends are set up differently. He stated that technically there was nothing wrong with the rear end at this point to justify a ring and pinion change which I took to mean that they had done all they were going to do for me. So I guess the next step is to write Chevrolet Customer Assistance and see if they are interested in satisfying me. The noise is a little better after it was worked on but still can be heard over the radio set at a moderate volume. Its annoying more than anything. Before it would start when coasting above 50 MPH, now it starts at about 50 and whines down to 40 MPH. I welcome anyone's advice or comments on this matter.

CMNTMXR81 · November 21, 2002

Did he check the pinion depth?

I set mine up real tight in terms of pinion depth on my 10 bolt and it howls like a S.O.B. but I have yet to pop it with 3k rpm launches (like the majority of people have been with these cars) at the strip as there is no slack in the gear.