Rear axle clunk

I assume my 76 m880 has a Dana 60 in the rear. The thing has a significant clunk when shifting between reverse and drive. Was this normally a fairly tight axle? I've a parts truck I could switch axles with (assuming it is in any better shape). I don't think I've the know how or tools to rebuild the differential.

...or should I just drive the beast and not worry about it?

Any input will be appreciated.

Check The u-joint at the rear of the drive shaft.....It is usually the first thing to go and easy to replace.

The u-joint is a good place to start. Check the pinion shaft to see if it can be moved side to side, indicating loose bearings. If this is happening, many times you will see oil leakage at the diff front seal. If all u-joints are tight and the pinion shaft seems OK, remove the axle fill plug and try to sample the oil to see if there are metal particles in it. Best yet, remove the rear cover and check it out. Spider gear problems are the most common cause if the problem is in the gear set. If the shaft comes out of the spider gear set, it can lock up the axle, sending you skidding out of control. You do not need a cover gasket to replace it, get all parts clean and dry and use an RTV sealant.

Can also be a worn chain in the transfer case

Yup, those did stretch and clunk the rear a bunch especially when the 318 was cold and the carb on high idle of about 1600

Well its been awhile, but I finally got a good look under there. The ujoints actually look good. I can't discern free play in any of the ujoints, though there appears to be everywhere else.

There is a bit of free play in both the front and rear differentials, there is some free play between the front and rear of the the transfer case that I will assume is the chain, and the splines on the rear drive shaft have a bit of play as well. I hadn't revisited this thread and forgot to check for side to side play in the pinion shaft. I noted that the seal on the front differential is leaking a bit, but the rear is not, though that is definitely where the loudest sound is coming from. When I shift into reverse, I can really hear two clunks in quick succession.

A suppose it wouldn't hurt to replace the pinion bearings/seals in both differentials, as well as the chain in the transfer case. How difficult is the job on pulling those bearings? Is there a particular brand of bearing that is hardier than others? For ujoints I like to go with Spicer, but just have not had to replace many bearings over the years.

Any extra input or comments will be appreciated.

If you are not familiar working on axles, I'd pass the bearing job on to someone else. They require a few specialized tools that the average mechanic doesn't have, such as cone bearing pullers and torque wrenches in the 250lbs + range. As for bearing brand, dig around and find or order Timkin bearings online. they are the OEM bearings and are well worth the extra money. I'd replace the driveshaft or have it rebuilt with a new spline shaft and yoke before I did anything. I would bet that is the majority of your problem. The accumulated slack in all the rear driveline will normally cause a clunk noise of some magnitude but the worn splines will multiply the issue and will only get worse as it tries to kink the shaft when force is put on it. Just be happy you have a Dana 60 rear and no the 9 1/4" axle that came in the 1/2 ton Dodge trucks.

And if you don't want to fool with that, CItizensoldier has new axles or at least he did.

Rebuilt my rear on my F350, and I agree with Elwenil; you would probably need speacial tools, I had to be creative and it was a true PITA. Course I repaced everything so I had shim everything and use micrometers, no fun. But the rear is much better now.

I ended up picking up a military rebuilt axle, as well as a rebuilt transmission. Took care of the problem. Appreciate all the input I received.

I never had a Dodge with an automatic transmission that did not clunk when you droped it in gear.
If it's not got too much slop you can feel & the U joint is good it's normal in my book

The "Dodge clunk" that is typically found on Dodge trucks is in 1/2 ton models and is a result of the pinion crush sleeve losing preload in the 9 1/4" rear axle. It's so common it's considered just a quirk by many. The D60 should not have enough slack in it to cause a clunk and if there is it should be addressed ASAP.