LMTV front axle clunking in mode while turning

[Keith Knight]

I have a 2003 M1078A1 with high speed gears and a rear locker. I’ve owned the truck for 8 years. In the last year we’ve traveled over 20,000 miles I’ve used mode countless times. The last few times when in mode for off road use slight turns left and right I’m getting very obvious clunking from the front axle, something I would totally expect when fully clocked left or right but it happening with slight turns. It did not do this in the past. I can say each time was on firm ground I haven’t tested it with slippery mud or snow. Any ideas what might be causing this? I spoke with a friend that uses his LMTV extensively plowing snow and much more putting in and out of mode and he hasn’t experienced this particular problem.

 

[GeneralDisorder]

Have you checked and greased the front outer hub u-joints? You need some special adapters to get at the zerk fittings.

 

[Keith Knight]

Yes I jacked up the front axle and turned the steering and rotated the tires to grease them just before this year’s trip in January 2024. Maybe more grease.

 

[Ronmar]

How is your overall backlash in the front? With the center diff locked out in mode, it is unable to compensate for the different arc/circles traveled by the wheels front to rear. With a locker in the rear it may be loading/unloading the driveshaft as it is dealing with different arc/turn radius from left to right in the back. The driveshaft loading/unloading may be felt thru the locked center diff and smacking a sloppy backlash in u-joint, slider or gearset to make some noise up front?

 

[Keith Knight]

Not sure what you’re asking about overall backlash? Ring and pinion back lash or what?
I’ve had the locker in for 6 years and I feel this is something new.

 

[Ronmar]

Overall, but it could be that one particular item has become sloppy and is causing the clunk...

I would also look at axle bushing runout adjacent to the axle u-joints at the spindles and ends of the axle housing. slop here could cause the axle to start smacking its housings, but it would probably have eaten the seals up though, so Hmmm...

Oh, and are all your lug nuts torqued? I had this happen on a tractor once, and the clunk led me to loose lugs...

 

[Keith Knight]

Thanks, yes the lug nuts are at proper torque.

 

[Keith Knight]

I’m hoping someone else has had this experience and found a solution or a cause.

 

[shawnspeak]

It's a long shot, but I found the locker to be fairly sensitive to tire pressure differences and differences in loading side-to-side. If I fill up my fuel and water tanks (that are on the same side) the locker will unlock/lock more frequently while turning. Adjusting loading or tire pressure to keep the upper rim of the tire the same distance from the ground (mostly) eliminates the issue.

 

[Keith Knight]

Thanks, I wish it was just the locker. I only have a rear locker. And it was definitely coming from the front axle. I was experiencing this while air down to about 55 psi on a gravel forest road. I only experienced the clunk in mode/ low range with the transmission locked up. Not in high range.