Rear end clunk when taking off - with a twist

[dwe8922]

First off, I have an '06 2500 duramax with the Allison, and 120,000miles. I had a '99 yukon that had the infamous clunk from the yoke, and when my '06 started doing similar, I thought it couldn't be with the Allison.

Mine only happens on take off. I recently replaced the rear end oil from Napa 75-90 Valvoline synthetic. That didn't seem to change anything; only when making a tight turn on my gravel drive; it seems to bind a bit in the diff. But, on pavement, there's no sign of binding.

From searching, I assume that my problem is from the splines on the yoke needing to be lubed. Today though, I parked in a depression, w/ one wheel in soft stuff. When I went to take off, I eased on the gas, and the wheel in the mud started to spin. I backed up a bit, then forward with more gas. A metallic pinging noise came from the rear, similar to when you go from park to drive in an old car on an incline. After the noise, the rear end hooked up, and put power to the wheel on firm ground. Does this mean anything, or am I looking at the common yoke lube problem?

Thanks!
David

[Charlie B]

The rear end locked up like it is suppose to on a slippery surface. One wheel spins and then the other locks for traction. Sometimes they do make strange noises when locking. Hopefully the truck is doing what it is made to do, some owners have alot of problems with there locking rear ends. Charlie

[freyguy]

Yup, I'm thinking that was just the rear end not locking in right away. It happens on mine if I start on the gas a bit quick. Sounds like you didn't nail it, but they are picky.

Lubing the splines is cheap and easy. I like to use synthetic marine propeller shaft grease. It seems to stay on the longest. And I always clean out the old grease with some brakeclean.

[dwe8922]

Thanks guys; I'll give the lube job a try. About how long does it take to do?

[dieselsmoker14]

when you changed the diff oil did you notice any metal shavings or particles in the oil or on the drain plug? mine was doing the same thing you are describing an the governor in the g80 had broken the splines off the small shaft making it lock rather weird on low traction surfaces.

[freyguy]

Lubing the shaft only takes about 30min. Jack up the rear end, take off the rear u-bolt straps (12mm I think), then remove the driveshaft. Take some Braklean and clean out the inside of the slip yoke, then reapply some new grease. Use a good bit too. Then re-install making sure you put the rear back on the same way it came off. You may want to mark it before taking it off. You may have to move the rear wheels to get it to line up. Mine always moves a 1/4 turn or so.

Another note, if your parked so your rear is slightly lower, sometimes when you pull out the slip yoke, a small amount of tcase fluid might come out. Might want to put a pan there just incase.