How much free play should be in the drive line? At times when shifting from 2nd to 3rd and 3rd to 4th I hear a slight thump.

I was under the truck today and there is a little play in the drive line. The U joints have no play but I noticed a small amount were the shaft comes out of the rear end.

The truck just turned 30K.. Any help would be appreciated.

 

There has to be a little play in the drive line, otherwise things would bind up. Now, how much play is something that can be difficult to measure. How'd you check the u-joints? I believe you should do it by taking all of the pressure off of them, and wiggling the drive shaft (twisting and shaking), preferrably with the wheels off the ground so you can rotate the drive shaft and wiggle in different places.
If they're OK, you will want to look elsewhere for the time being. Engine mount, tranny mount, etc. for something loose/broken.

Maybe someone else can tell you exactly how much free play should be in the pinion gear.

Chris

 

Chris,
I had the wheels off the ground and twisted the shaft and the U joints seem fine. The problem, if there is one, happens when letting off the clutch from a stop in 2nd and sometimes, not all the time, when shifting from 2nd to 3rd and 3rd to 4th. If I'm REAL careful when letting out on the clutch it wont happen.

I only have noticed it when the truck is empty..When pulling the 5th wheel trailer it never happens.

 

At 36K my truck blew the mid-ship bearing on the rear drive line, started out with light clunking, very subtle at first between shifts and during decelerating/down shifting, worsened over a few days to very noticable...thought it was a u-joint but couldn't find one that was sloppy. Had the dealer check it out and they said it was the mid-ship bearing and had to replace the entire driveline from xfer case to the rear pumkin as an entire unit (why I'll never know) but $1800+ in parts is what they charged against the warranty.. Might just be worth checking out.

Dave