I have a well maintained 240 Wagon with 5 Speed that has started making a rapid ticking sound from the rear end on deceleration. I checked around under there and found that the pinion flange has about a 16th of an inch of side to side movement and knock. The diff was still full of clean lubricant, and surprisingly the seal seemed to not be leaking. The diff sounds quiet on the highway, but the driveshaft does feel like it might be going off balance. The u joints seem fine and I replaced the center bearing, rubber housing, and rubber coupling last y

Is it possible, that I could get away with simply re-adjusting the pinion bearing pre-load (and maybe replacing the seal while in there)? Based on the serial number, it appears to be a non-crush sleeve model. I am hesitant to start a full diff rebuild, and any local rear axles that I might find are likely to be very rusted compared to mine. Suggestions?

UPDATE: I went ahead and disconnected the rear of the driveshaft to see if there was any scope for tightening the pinion nut. Didn't seem so. With the driveshaft off I decided to give the pinion flange a good shake to better assess how much play there was - none! I put it all back together and realized that the movement and knock was actually in the rear universal joint. I will replace both and see if the rapid ticking on deceleration goes away. Fingers crossed!

Thanks, it was indeed a bad U-Joint. Replaced both rears and knocking gone. Yay!

Had the same noise in '88 240, 185k, m47. U joints too. Year later pinion seal started leaking. Same shop replaced. Still leaked. Put in sleeved yoke. Stopped. Year later whirling noise started up getting now to a nice musical whine/ howl. Took it back, said it needed whole new bearing kits including wheel bearings. Scatter shot approach. I'm waiting for warmer temps to have a look myself.

What usually goes awry is what was last worked on. Sounds to my ear like the ring gear is not lined up with the pinion gear. An aside, a Dana rear end like this, as far as I know, should be bullet proof with our little torque and hp.

I didn't really want to say anything as I'm not very diverse in knowledge of differentials as I said in a post to Trichard a few days ago.
Most gears trains do not make a ticking sound unless there is foreign material in between some teeth. Usually an equally hard piece of tooth, bearing flakes, a cracked locking washer or even a stray sliver of shim from a careless mechanic.
Even a rag or saw dust runs quietly for a while.

A bearing can make a noise first but of an lower order of magnitude when compared to a broken tooth piece.
Gear slop clack or clunk or the term "backlash" does not usually happen to make a noise unless the load on the teeth changes directions or shifting occurs against thrust bearing surfaces.
On large helical setups preloading of tapered bearings is an important process to dial in the strike area of teeth.

Your description of ticking does sound more like a few needles in the universal joint that's gone bad. The needles suffer dryness for a long time. I have seen joints where the needles have almost rusted into dust. Its amazing how they stay quiet and then will clunk or knock and the driveshaft slip into out of balance.

I think you were paying attention and this may have prevented a castrophe from happening sometime later.

Crossing fingers, legs or eyeballs might be a technique to try in this case, so it turns out simple!
(:-)
Have a nice drive!

Phil