u-joint, transfercase, or what?

I have an 86 s-10 blazer that is making a clanking sound when I put it in drive or reverse. I got under it and moved the drive line back and forth and it does'nt seem to move. I haven't noticed any vibration or anything. I't seems to be getting worse. Any help would be appreciated.

I had the same problem when shifting to drive or reverse, it would make a clank/ping noise. Get back under there and grab one end of the drive shaft at a time with both hands and lift up, pull down, pull right, and push left. Then grab it with both hands and try to rotate it back and forth, while observing the universal joints at the receiver and carrier for any amount of play

Are they original stock joints? Being an 86 they should have been changed at least once or twice.

Do the joints have grease zirk nipples. If they do they should be greased on interval with a chassis lube.

I just went back under there and tryed to move it around but nothing, it fills real solid. As far as I know they are original joints. They don't have grease zirk nipples.

How many miles are on the truck and does it make any clunking or clanking noises while you are driving or if you hit a bump. Especially if you hit a bump while taking a corner?

My Blazer has about 170,000 Miles on it. It does'nt make any noise while driving or when I hit a bump. I'm not sure what it could be. hopefully it's not nothing to bad. By the way NOVA71 nice Nova.

I still have this problem can some one help?

You can also, besides the U-joits, Have excess clearance between the ring and pinion gears in the differential. Jack the rear off the ground ( safely ) and twist the drive shaft back and forth. You will feel the gears slap together. The number of degrees you have to turn the drive shaft across the tooth gap is the play you have in the gears. Too much play creats the backlash when switching from forward to reverse. Shows that the pinion gear is worn badly or out of adjustment.

I took the drive shaft off and wiggled the pinion and it seems fine. there is a little noise coming from the transfercase though. Any idea what it could be?