I have a 2005 GMC Sierra, CC, Z71, 1/2 ton. I noticed a strange clunking noise a few days ago coming from under the truck. The noise occurs when I hit the brakes and let off quickly...almost like slack in the drivetrain. I wasn't sure if it was coming from the front or rear. However, when I got home from work today I pushed on the rear of the truck, side to side, and I could hear the noise coming from the passenger side rear wheel area.

Upon further inspection, it appears the axle is actually sliding in and out about 1/8-1/4". Basically, there is play in the passenger side axle. Is this normal for these trucks? The truck has 11k miles on it. The reason I'm asking is because I'm supposed to go on a ~ 300 mile trip tomorrow in the truck, and I wanted some opinions. If I was going to be in town, I'd just take the truck to the dealership. Thanks.

 

Sounds like you have a worn out side gear (open diff), or shot clutch plates (G80 diff, locking). Remove the diff cover and inspect the differential for any metal flakes and take a look your differentail.

 

If you have play like that there has to be some internal failure. If things have come loose enough for the c clip to fall off the end of the axle you are going to have a bad day on a 300 mile trip. The axle and wheel will walk out the housing and pass you on the highway