Ok, its an 1981 short box 4x4, it has always had this problem since I've owned it. Driving in 4WD (LO or HI), there is a very loud clunking / thumping / snapping sound that gets worse if I turn a sharp corner or drive straight under load (ie: up hill). It sounds like something is tightening up, then suddenly releasing, like a driveshaft 90 deg. out of line....
If I put the truck (axles) on jack stands, shift to drive 4WD, no noise whatsoever. It only happens when there is load to the front wheels. And 2WD no problems at all.
So I suspected front diff, inspected it, no problems. Eventually replaced the entire third member. Same noise. Suspected front driveshaft. U-joints were good - no play and double carden joint seems OK too. Went through the front end birfs, axle shafts, spindles, and ended up replacing the entire front diff, hub to hub, including the diff (again), with a rebuilt '85 diff & housing when I put in Hysteer, same noise. Then suspected transfer case. Replaced it, same noise.
The only thing I havn't replaced is the front drive shaft. Although the welding along the flanges does not look factory, the U-joints line up and well, can't fault it. Is there a special way to line up U-joints on double cardan shafts???
I don't have a picture of the shaft but some pics of the truck and mods here: http://81tsb.tripod.com/ Again, it was doing this before ANY mods were done. Please help! Thanks.
If I put the truck (axles) on jack stands, shift to drive 4WD, no noise whatsoever. It only happens when there is load to the front wheels. And 2WD no problems at all.
So I suspected front diff, inspected it, no problems. Eventually replaced the entire third member. Same noise. Suspected front driveshaft. U-joints were good - no play and double carden joint seems OK too. Went through the front end birfs, axle shafts, spindles, and ended up replacing the entire front diff, hub to hub, including the diff (again), with a rebuilt '85 diff & housing when I put in Hysteer, same noise. Then suspected transfer case. Replaced it, same noise.
The only thing I havn't replaced is the front drive shaft. Although the welding along the flanges does not look factory, the U-joints line up and well, can't fault it. Is there a special way to line up U-joints on double cardan shafts???
I don't have a picture of the shaft but some pics of the truck and mods here: http://81tsb.tripod.com/ Again, it was doing this before ANY mods were done. Please help! Thanks.