help! grinding noise unknown orgin.

[sierra559]

Hello to everyone, I have been using this forum and several others trying to figure this problem out but have not had any luck so I decided to register and ask other drivers if anyone has had this same problem. So here is the problem, I purchased a used 2008 gmc sierra 4.8 crew cab. Recently i began to have a problem with it. Sometimes when i make a complete stop and try to take off rapidly there will be a loud grinding noise but the truck will not take off until the rpms decrease. It sounds like the drive shaft is still spinning though not quite sure though. I took it to the dealer and had the drive shaft, u joints, slip yoke, differential, and transmission checked and scanned. Dealer said nothing was wrong and was unable to reproduce the problem and serviced and lubed all components. I drove the truck and today it did the same thing but this time i was driving through a wet parking lot and the floored it and it did the same thing. It sounds like something is spinning and something is trying to engage and it engages when the rpms decrease low enough for something to engage and finally the truck will take off. Can this be something having to do the traction control? I am pretty annoyed with this i have even considered trading it for a 2014 but I like the truck and would prefer to fix it and keep it. The truck has 60000 miles but is no longer under warranty. I have searched all forums and google without any luck. Amy help or suggestions or anyone with the same problem? Thanks in advance.

[8.1HD/ALLISON]

Definately not the traction control. Sounds deep to me. Guessing transmission, or transfer case. Sounds like somthing is slipping. Take back to a competent dealer and take a mechanic for a test drive so you can show them.

[sierra559]

This is the second dealer I take it to. Both have done the same exact thing and of course the damn truck doesn't do it while the tech is riding with me. I got the differential checked and it was fine i guess. Im going to get it inspected again though. Traction control crossed my mind since all the times this has happened the wheels have spun a little. Would it have a transfer case even though its a 2wd?

[ttopcamaro86]

Sounds to me like a problem with the locker differential. It will not engage at high rpm to keep from snapping things. Try searching for g80 locking differential and see if that may be the culprit. (G80 is the rpo code)

[ttopcamaro86]

http://www.gm-trucks.com/forums/topic/104344-limited-slip-rpo-g80-troubles/

[sierra559]

I just checked the rpo codes in the glove box and g80 is not one of them. Its actually a gu5 jf3

[8.1HD/ALLISON]

2 wheel drive does not have transfer case.

[sierra559]

It doesnt do it as long as i press the gas slowly and only does it when taking off from a complete stop. It feels as if the transmission kicks out of 1st gear and when i let off the gas and the rpms drop the transmission grabs and takes off. All other gears shift fine. I have been thinking of installing a shift kit to see if it might help but not sure if there is one available for this truck.