guys,

I have an 05 Tahoe Z71 with 84k on it. last couple weeks, I've been getting a pretty substancial vibration when the engines at lower RPM's and lugging. If I make it downshift or start to coast, it quits. I changed the rear diff fluid as a machanic suggested that anyhow. THe fluid level was a little low, but there were no shavings in it and the gears all looked good. I know with the limited slip diffs, there's clutches in there, but have no idea how to check them. Also check U-joints, they are all tight and look good. Checked fluid in the transfer case and it looks good. Any suggestions??

 

Did you change your exhaust recently?

 

no, it's original as far as I know. All looks good, no rust or holes.

 

Flexplate issue?

 

maybe, is that common in the GM's? I've never had one go bad on any vehicle. Could the limited slip diff be the cause? I'm not sure exactly how they work or how to check them.

 

I asked if you changed your exhaust because I though you might have been experiencing Drone which is sometimes perceived as vibrations.

Since you say vibe goes away on decel it is most likely U-joints,slip joint on drive shaft,trans tail shaft bearing.

Unlikely would be broken leaf spring or even worn shocks.

You see when you accelerate the differential pumpkin rotates upward throwing something out of phase which produces the vibration if any of the above are toast.

When you let off the gas everything goes back to static-being unloaded and the vibe goes away.

Chasing down vibes can be a daunting task and takes a lot of patience.
Even added and 2* angled shim above the leaf spring mount can work in some cases.

 

The G80 diff is a locking, not limited slip, diff.

Eaton G80

 

The truck only vibrates when i am on the gas, but running at low rpm's, so the trucks lugging. when it's at higher rpms, or has no load on it and coasting, its fine. I tried turning the tow mode on, which should no allow the truck to go into overdrive, correct? It still does it.