Big clunk when engaging D or R

[Teal4x4]

I have a '93 XLT 4x4 push-button 4.0L V6 auto ext cab with 143K miles. When I shift into Drive (in 2WD), after almost half a second there's a lurching clunk as the tranny (I'm guessing) engages. Same for Reverse; - shift into R and about a half second later theres a clunk. It feels like it's taking up slack in the driveline. I looked at the U-joints and can't see any slack/play. It's a single-piece shaft. Looks clean and no signs of damage or leaks. There is no such clunk on accelerating or decelerating. Even at low speeds I can apply and let up on the gas without any slack/clunking. The truck otherwise drives smooth and tight. It only makes this clunk when the tranny is engaged.

Any ideas? I've searched the forums top no avail on this one. lots on clunks, but none with my symptoms.

thanks in advance for the help.

 

[Teal4x4]

Bump.

Any input anyone?

 

[gotmudd]

park on level ground and block your wheels, with truck OFF and in nuetral slide under and grab your driveline and shake it up, down, side to side and try to rotate. it should spin but you should feel no play at the bearing caps. visual inspection doesn't always work, it's a hands on thing. it sounds like the begining of u-joint failure, although if your u-joints are tight it may be that your idle is too high. as for there being no noise on acceleration or decelleration they may not be too bad yet. i have seen them, when bad enough, make a 'chirping' noise on acceleration accompanied by a vibration. you stated it most accurately by saying it sounds like the driveline taking up slack, your u-joints being the weak link, if they are starting to wear that is exactly what you are doing is taking up the slack. just my 0.02