1999 Sierra 5.3L 4x4 with what I think is a transmission issue but I can't tell if it is that or my transfer case.

Issue: Very rapidly my truck just started grinding like crazy in reverse. It sounds like a gear stripped (sun gear or rear planetary set maybe)? I noticed my speedo is climbing as well when in reverse but i'm not moving...

The trans only has 40K on the rebuild and has the "beast" sunshell, upgraded servos, clutch packs.

Does anybody know what would cause it to grind in reverse like that? Does it sound like more of a transmission issue or transfer case?

Thanks

 

The VSS (speed) sensor is located on the trans output shaft. Therefore if your speedometer is reading but the truck is not moving, the problem is after the output shaft. So, yes, sounds like the transfer case or differential.

 

only in reverse?

 

That is puzzling, but even if the truck has the VSS somewhere else, it has to be at or after the output shaft.
Without the stranger speedometer behavior I would also suspect something in the trans, like the sunshell.

 

Thanks for the reply guys. Actually, i now noticed it is happening in drive too...but i can move a little before the grinding starts. In reverse, it won't even move.

I thought the VSS was on the transfer case for 4WD? If so, I guess that does mean my trans is spinning the output shaft?

I'm planning on trying to pinpoint the grinding to the T-case or Trans with an electronic stethoscope. Will report back.