Singing Rear End

[Super 8]

I purchased my 2001 GMC 2500 HD 6.0 new, it now only has 58,000 miles. I noticed the rear-end tends to be worse as far as a singing/howling noise though second gear, which is a automatic. I have serviced it @ 20,000 miles with fresh synthetic oil. One odd thing that happened last winter when towing was my center hanger bearing went out. Any input would be great, thanks Les........

 

P.S. I know of another 2004 model that sounds the same.

[8.1HD/ALLISON]

Does it only make noise in second? or in that speed range. If it only makes noise in second, probably not the rear end.

[Super 8]

The noise quits as it shifts into second emply, thru second if I am pulling something. I even changed the muffler grasping for straws.

[ChevyTech77]

The 4L80E transmission, such as what is installed in your truck, has straight cut gears for LO or first gear instead of helaical cut gears like 2-4 and most every other auto transmission has. It is a trick taken from the Allison transmission's playbook for strength. Straight cut gears while stronger, are much noisier than their helaical counterparts therefore, you will only hear that noise in first gear and it is totally normal.

[Super 8]

The 4L80E transmission, such as what is installed in your truck, has straight cut gears for LO or first gear instead of helaical cut gears like 2-4 and most every other auto transmission has. It is a trick taken from the Allison transmission's playbook for strength. Straight cut gears while stronger, are much noisier than their helaical counterparts therefore, you will only hear that noise in first gear and it is totally normal.

 

Thanks for the input!