Clunk! and Sliiiiiiide -- Where to start?

[77Jimmy]

Ok, I’ve searched the forums and couldn’t find my exact problem (or problems as it might be). Please help me understand if the two issues below are related or not.

The Clunk
When I go from Park to Reverse, I get a loud clunk. From Reverse to Drive it’s a bit smoother. No clunks, clicks or any weird sounds when I'm driving, only happens when I move through the gears (auto tranny). I suspected U-joints after reading some other posts. So a while back, while I had it in the repair shop for something else, I had them check out the U-joints while they had it up on the rack. They said the U-joints were fine and that it was normal for there to be some slack in the rear end. I am getting uneasy about driving it around not knowing what the exact problem and solution is, not to mention it just bothers the heck out of me. Where would you suggest I start looking for the problem?

The Slide
Starting from a stop light/sign, I can feel the entire truck kind of slide back a bit until it, for lack of a better term, “catches” or comes to rest on something. I try to accelerate slowly so I don't blow something up. I’m thinking something in the driveline?

Thanks!

 

[76chevy]

Put your emergency brake on, then put the trasmission and transfercase in nuetral. Get underneath your rig and shake the rear and front drivelines by the slip yokes. If you have movement then you probably need your slip yoke replaced.

Also check your idle. If it is high you can get the clunk. The clunk is pretty common on these trucks. If it is severe then you have a problem. I'd also have the pinion checked.

 

[Butch]

Other possibility might be loose U-bolts.

 

[Blue85]

Usually "the clunk" comes from loose spider gears in the rear differential. Some is normal. It will of course be the worst when chaging from forward to reverse or vice versa. Is your truck full-time 4WD?

As for "the slide", could it be that the rear brakes are hanging up a little?

 

[77Jimmy]

I'll check the spider gears. Assuming they are really loose, do I have to get a whole new axle? Sorry, that may be a dumb question, kind of new to this. I have part-time 4WD through a converted np203.

The slide doesn't feel like a brake thing. It's hard to explain, just feels like the truck slides back and sits down.

 

[CooknwithGas]

I had that exact same problem and changed out five U-joints - three on the front drive shaft and two on the rear driveshaft and it took a lot of the clunk out of it. The old u-joints didn't appear to have that much play in them, but maybe all together, it makes a difference.

I hope this is your problem too, because it's relatively easy to fix. I'll give you some tips on the u-joint change if you need them.

Right now I've got that heavy-pig of a transfer case out of the truck so there's no clunking going on at all!

Good luck.