Bad sound from kubota

I was doing usual evening chores this evening and while digging a bucket of grass silage from the pile I heard and felt a clunk from the rear end. It continued to clunk while moving in 4wd and runs fine while in 2wd. I'm not sure why the 4wd problems sound to be coming from the rear axle but I do know it is not good. Any thoughts to how serious it will be to fix it? I'm sure there's likely a stripped or chipped gear or input shaft but not sure why the sound is coming from the back? It's a kubota m8200

No way to know from available information.

Dean

Check all bolts on the wheels a loose one can make funny noises i would check that first

I will definitely have a look at the bolts in the morning,if it's not something easy like that there s no guessing until it's apart thank you very much.

2X wheel bolts.

For a wild guess, I would suggest jacking up and turn one rear wheel at a time with the transmission in gear (engine off) to check for a broken tooth on the bull and pinion gears. Maybe in 4WD it takes the tension off the rear bull & pinion and minimizes the "clunk".
If this is the case, DO NOT use the tractor as is.

K-Mo

I would check with a good Kubota mechanic or a Kubota dealer. They should be able to diagnose the problem from the symptoms.

If the 4wd is engaged with a clutch in the tranny, then it may well be something in the 4wd. Remember, it's gotta get it's "spin" from the tranny.
AaronSEIA

MOST common clunk is as someone suggested "Loose bolt where the wheel dish fastens to the rim. Now that being said with the fact that you noise changes from two wheel to four you probably have a different problem. Again as the other poster suggested get it jacked up off the ground and with transmission in neutral turn each rear wheel and listen for noise. Final drive or bull gear failure is very rare on that unit. Worst case is probably a bearing busted but the sooner you find and fix it the cheaper it will be.

Not too often a person gets lucky with tractor problems but this time we actually did! I took some advice on here and talked to the Kubota mechanic. The problem is luckily simple and fairly cheap. There is a drive shaft under the tractor running from the transmission to the front drive axle. On each end of that shaft there is a sliding internally splined coupler that connects the shaft at the front to the axle drive spline and at the back to the output shaft at the transmission. Those couplers once the roll pins are pushed out slide onto the drive shaft and it can be removed. The coupler at the axle end was stripped clean at the end that goes over the axle spline and that's what turns out to be the noise and loss of 4wd. The mechanic said that shaft can be removed and the shield put back in place and the tractor can be used as a 2wd while the new couplers are on their way. Apparently that is a fairly common configuration of many 4wd tractors and those couplers are made of a softer metal than the gear splines to act as a shear to protect the really expensive and hard to replace internal parts. Thank you to everyone for the help to get pointed in the right direction! We may grow old but never too old to learn something new every day lol

Diff lock partially engaged?

Hmm...