4 wheel drive rear axle noises

[nyjet29]

I bought my trac used with about 40k miles on it. Ever since i got it, ive noticed that when I'm driving on soft dirt in 4 wheel high I hear a lot of clunking sounds coming from the back axle. It doesn't happen in 2 wheel drive at all. Any ideas on what that might be would be appreciated.

 

[ncranchero]

Either a bad U-joint or excessive pinion backlash. I'd say u-joints first. When in 2WD the rear drive shaft and differential is doing all the work, when in 4WD it has help from the front. Thus driving on soft terrain allows one end or the other to slip a bit with the "work" going back and forth between the two. On a 4WD vehicle the front gear set ratio is a point or two higher so it will always be "pulling" instead of the rear end "pushing".

That's my story ................ and I'm sticking to it!