Originally Posted by A7X

A 9.75 from an 02+ FX4... 3.73 LS, disc brakes...

'97-'98 9.75 had smaller pinion bearings, smaller axle bearings and 12mm lug studs... They were thrifty and used the same bearings as the 8.8...

Your pop in the rear could be many things... From your ubolts being loose/stretched or a bad tranny mount to a bad pinion bearing...

Check ubolts, check leaf bushings and shackle eye bushings, all external parts etc...

I've seen the tranny xmember crack just under the mount where you can't see it until you pull the plate underneath, (2) 18mm bolts and take a peek... That'll make a knock when letting off the gas as well as a bad mount...

Raise the whole rear off the ground, grab the drive shaft and push up and down, feel for play in the pinion bearings...

Pull the drive shaft and lube the splined end on the slip yoke

Then pull the diff cover after you've checked everything else and take a looksee...

Originally Posted by Carcrazygts2

One correction 97-Early 00 used 8.8 axle bearings only. Still had the smaller Pinion and carrier bearings.