Newbie help. Driveline lash...trans or transfer case issue!?

[CapCharter]

Recently purchased a 91 Fj80 w/ 220k (loving it!) and since day 1 of owning it, when I shift into gear from park it makes a pretty good “slam”...especially if I have my foot on the brake. A similar lash or slam happens when I cruising along and take my foot off the gas then apply throttle to get back up to speed.

I always assumed it was a u-joint or something in the driveline, so I took it to a local mechanic, he put it on his lift and shows me that when the vehicle is shifted into gear, the transfer case appears to be moving a bit.

It was recommended to me to have the transfer case rebuilt, which is fine...if this is really the issue. Thoughts?
Thanks in advance

 

[SUMMIT CRUISERS]

Most 91’s and 92’s have “the clunk”. Wouldn’t worry much and don’t waste $ rebuilding your TC. Might want to check front drive flanges and driveshaft slip joints for slop.

 

[ppc]

The 91-92 models typically do make noises because they don't have the viscous coupler in the transfer case. It is caused by the combination of all the tolerances/slop of the various driveline parts. The transfer case itself is usually bullet proof provided there is no leakage from the seals or play in the output shafts.

That said there are some things to check:
A lot of the movement can be attributed to worn drive flanges/birfields on the front axle or lack of lubrication
The slip yokes and U-joints on the driveshafts that need lubrication or replacement
Turn up the volume on the radio

 

[Cruzilla]

I would check the slip yoke on the drive lines first... they do wear out!

 

[cjmoon]

Front drive flanges early ones are shorter so less spline engagement. If you go new. New birfs and flanges needed for the upgraded newer style.

 

[bajaphile]

First thing would be to start pumping grease in all the U-joints. How many pumps does it take for you to hear the popping of the old grease?

Slip yokes for me is a bit of a dark art, I usually go until I just see the yoke barely move and immediately stop. (You can remove zerk if you added too much).

I'd then go for a drive and see if there is any change. Gotta start on the super easy things first!

 

[jonheld]

he put it on his lift and shows me that when the vehicle is shifted into gear, the transfer case appears to be moving a bit.

What do you mean by "moving a bit"?
The transfer case is bolted to the transmission which is bolted to the engine. The entire assembly is rigid.

 

[Irish Reiver]

when the vehicle is shifted into gear, the transfer case appears to be moving a bit.

View attachment 2389962

Did your dude check the transmission and motor mounts? There isn't really any other way that the transfer case can move

 

[mudgudgeon]

Agreed with most of the above.
Transfer case are bullet proof for the most part.
Greasing u-joints and slip yolks can give temporary relief. If it helps, you've narrowed down the wear to u-joints.

Most likely culprit of drive line backlash is the birfs and drive flanges on the front hubs. early models had 25mm of spline engagement, 94 and later had 35mm of spline engagement with longer birfs and deeper drive flanges.

It's easy to check for slop at the drive flanges by jacking up one corner, popping off the dust cap on the hub, removing c-clip and rotating the wheel to watch for play at the end of the birfs.
Any play here is amplified