something clunks when accelerating and braking in driveline

[gmc4x4can]

So after a 9 month job on my truck (new cab, disc conv on front, lots of new interior parts) I finally passed the inspection here in B.C. What a relief. Since it wasn't drivable when I got it, I'm just learning some of the quirks driving it. The big one is there is a clunk when giving it gas, then you can feel it unload when you let off or brake, and it will clunk when you give it more gas again. there is play in the driveline somewhere. I can turn the rear drive shaft quite a bit by hand before it locks, where as the front drive shaft hardly moves at all. Truck came with two sets of diff gears, and two empty boxes that said posi, wonder the clunk is a result of that?

[LockDoc]

Originally Posted by gmc4x4can

So after a 9 month job on my truck (new cab, disc conv on front, lots of new interior parts) I finally passed the inspection here in B.C. What a relief. Since it wasn't drivable when I got it, I'm just learning some of the quirks driving it. The big one is there is a clunk when giving it gas, then you can feel it unload when you let off or brake, and it will clunk when you give it more gas again. there is play in the driveline somewhere. I can turn the rear drive shaft quite a bit by hand before it locks, where as the front drive shaft hardly moves at all. Truck came with two sets of diff gears, and two empty boxes that said posi, wonder the clunk is a result of that?

Block the wheels, put the transmission in neutral and try rotating the driveshaft back and forth. You should be able to see where the slop is then. Could be U-joints, rear gears, and/or carrier bearing. Also push up on the shaft close to the carrier bearing to see if the rubber cushion is shot....

LockDoc

[silverstreak]

Have someone shift from drive to reverse with the engine running while you look under the hood. Check for broken / loose engine mounts.

[snipescastle2]

Gotta be careful with the differential gears, seen a Fellow a few years ago he put a different set of gears in the front that weren't the same as the rear end, the drivetrain started binding up as he put it in 4x4, once he put it into 2wd high.
Have a good one.
Ben

[beautimus]

form the way you describe it, i would have 2 prime suspects.
1. the u-joints. if they are worn, then they will react to loading and unloading in the manner that you describe. but then, if you have rebuilt them earlier andf they dont have a bunch of milage on them, that may not be the case.
2. problems inside the rear diff.
the ring and pinion could have a bunch of slop, as well as the cross shaft could be loose in the carrier. also, the the retaining bolt for that shaft could be loose, or broken.

please keep in mind that i am not an expert here, and these are only suggestions based on what i would check , given my limited knowledge and experience. good luck !! oh and nice truck !!