1999 F350 CREW 4x2 6 speed manual w/dana 3.73 DRW

Started hearing a clunk after I towed my 5th wheel (35’ 3 axle,electric brakes about 12k weight). While cruising and in any gear when I letoff the gas and then accelerate I hear a clunk. I got underneath the truck and Ican twist the drive shaft a ผ inch each way and I can hear the same noise (frominside trans). It shifts fine and its strong – not sure what the problem is orhow to fix it.

Transmission has drain plug on bottom and the fill plug is about centermiddle on driver side. Cant tell what model number it is…

Suggestions welcome!

 

From the info you posted I just have to ask this question as a formality because you seem to have checked everything, and that is what about the u-joints? Some gear slop is normal in a manual trans. If you put the trans in gear and then check for driveshaft movement, what do you hear /feel as far as excess ply ?
Did you check the lubricant level in the trans?

 

The transmission is the old E4OD. I don't think a drain/refill will help this problem. BUt, Hanky has a good point I can expand on a bit.
With the driveshaft out, twist the input (pinion) shaft and see how much play there is. While I can believe (very easily) the transmission is loose, the rear axle can duplicate this very concern and be hard to diag.

 

I tried to check oil but the plug is kinda stripped so I stopped. This will go to shop for a new plug and oil on a lift. I looked at the E4OD trans and I don't have a pan on mine. So, that's still a mystery. The joints don't seems bad but the noise is inside the trans.
I guess Ill have the shop take care of this -

 

btw - its a 1999.5 (born on 4/1999)

 

E40D is an automatic, and was gone by 99. 1999 would have a 4R100 (an upgraded/updated E4) auto. The 6 speed manual trans was the ZF..

There's going to be some 'normal lash' in the manual trans, 'excessive' may need to be determined. With the drive shaft mounted, your not really going to be able to correctly gauge movement. This isn't a 4x4?

If there's no excessive rotation/lash and no abnormal noise/s emanating from the trans, possibly just a simple lube sample to check for suspended metals or trash in the mix..

With no 'new' noises, shifts are 'clean' meaning no hard shift/grinding issues, then could be clutch/pilot/flywheel, or even out back, cross member, rear mount, joints, loose input yoke/shaft and so on..

 

Sorry, I still call the automatics by their original name. To me, there's very little difference between the E4OD and the 4R100 (except the drums; they were all always burned up and the O/D snap rings were misplaced).

 

Its not a 4x4 and its a hand shaker not an auto. Like I posted earlier - I got underneath the truck and I can twist the drive shaft a ผ inch each way and hear noise in the trans. I can pull the shaft this weekend and check joints etc....

 

Got back from shop - the oil replacement worked. However, been driving it for a couple days and it grinds in 2nd and 4th on the downshift - if I wait a few seconds its not so bad. But if I clutch and shift down it will grind.