I have a 1996 Ford 1 ton F350, 7.3L DieselQuestion:  I thought I had a bad pinion yoke I hear the famous clunk when engaging reverse to low gear.  I dropped the rear of the driveline to check the splines in the pinion yoke, they look pristine, what wrong?Answer:  Worn Spider/Side GearsExcessive wear brought on by excessive mileage, misuse or poor or contaminated lubrication. Noise show itself just like pinion yoke clunk, once you have removed the driveline from the rear differential and can't see any spline damage the problem is probably worn or damaged side/spider gears.Replace of the spider/side gears. You want to order a new “internal kit” this kit will include 2 new spider and 2 new side gears, cross shaft and locking bolt. This is probably the simplest part of the rear differential to repair, drain fluid, remove the rear cover, with the rear tires taken off, you now have to remove the axles, if you have “C” bolt axles, push the axle in slightly and look into the center section the place that the axle comes through the spider gear you will see “C” clip remove it and this will release the axle and now you can removed. Replicate same operation on the other side. Now you can remove the cross shaft locking bolt and drive out the cross shaft, the spider and side gear will fall out. Reverse this procedure to re-install these gears.  You can see the rear end part that we can provide for your differential on out site.