1986 K2500 Loud clunk when in reverse

[Captain J]

I’ve a 1986 GMC Sierra K2500, with auto transmission, when in reverse a loud clunk is felt and heard in the drive shaft.
Any solutions how to fix it. Thx

[RotaryRocketeer]

Does the clunk only occur the instant it pops in gear, or the whole time it's in reverse?

If only when it pops in, check u-joints for play/slop. Spicer brand is the best you can by, in my humble opinion, should they need replacement.

[Captain J]

Originally Posted by RotaryRocketeer

Does the clunk only occur the instant it pops in gear, or the whole time it's in reverse?

If only when it pops in, check u-joints for play/slop. Spicer brand is the best you can by, in my humble opinion, should they need replacement.

Thanks for your reply, only when pops in reverse. I’ll re-checked them again.

[wilkin250r]

Get on a fairly level surface, then block the tires to keep it from rolling.

Put the transfer case and transmission in neutral, but lock the front hubs (if you can).

Then you crawl underneath and start moving and twisting driveshafts and u-joints.

I have a significant clunk when I shift into reverse, also. My clunk is a bad ring/pinion setup in my front axle, I got about 15-20 degrees of free rotation, but I haven't bothered to fix it yet.