Crazy drivetrain vibrations. Feels like it's falling apart

1994 Cherokee xj 4.0
175k miles
3.5" lift
No sway bars
Stock tranny, tc, and driveshafts.

So, I recently installed a new motor and re-installed the tranny. When re-installing the driveshafts I made no effort to mark them installed them back. Driving around the neighborhood (not chancing road speeds) it shakes and vibrates pretty bad. Very noticeable. Let off gas while coasting downhill and problem didn't change. Seems to be the worst between 10-15 mph.

I'm guessing I have multiple issues here given the other problems I've had. I know it has no sway bars (front or back) and a couple of the shock bushings are failed up front. I'm thinking this issue is coming from the transfer case, u joints, or driveshafts.

I'm going to pull off the front driveshaft and see what happens on a road test. If no change, I guess I could pull the rear driveshaft and drive in 4hi to test that. Any other ideas?

I'm going to remove the front shaft then check this post.

I have old mud terrains with flat spots on it now. It's hard to diagnose road noise from car noise. Maybe jacking up rear and driving in place would help? I don't have street tires to swap.

As already noted in another thread, I have a tendency to reinstall things incorrect. It's possible I did that here. Not ruling anything out. You guys were awesome in helping me diagnose my transmission install screw up! Thanks in advance!

You might have unseated one of teh driveshaft u-joint caps in the yoke, that will shake things pretty good

Another thing you can do is put the transfer case in Neutral and run the trans in Drive, won't go anywhere but it will tell you if teh shakes are coming from inside the trans (probably not)

It's worth a shot. I'll inspect closer. Just looked for play a minute ago. Couldn't really find any except at the slip joint going into the transfer case. It wiggled a little. Yanked the rear out first as I wasn't sure about that play.

Stupid question: if I pull the rear driveshaft, fluid comes out. How could I drive with just the front driveshaft and not leak a crazy amount of fluid? Just emptied the tcase fluid. Going to buy more. Thought I had enough dex 3. Figured if I was down there, might as well change it. Going to topp off the diffs too. But one at a time. Want know exactly what my issue is instead of fixing everything at once.

And I don't suspect the tranny, but, who knows. Worth a shot.

some people have been able to put a juice bottle cap in the seal to keep it from pumping out, but I never could find anything that worked that well

Yea. I'm not going to try it. A quick search and i could have saved myself the trouble. Ha.

On a good note the u-joints look great. Smooth rolling. Inside the teeth look good on the driveshaft. I did notice this...see the pic. I can't find a corresponding groove in the transfer case. Did I not look close enough? Looks like this should only be lined up the right way....

that doesn't matter

all you did was swap engines? I'd look there. Motor mount loose, bad vibration dampener, something like that

Yes. Just swapped engines. Well, a year ago. It's been sitting for a while as I tinker with it. Engine mounts are brand new. It's definitely coming from the transmission back. Feel it more up front. I'll know more once I jack it up and let the wheels spin. Started raining here so I was cut off from progress.

Anyone know what size bolts hold the front driveshaft to the transfer case? Looks like 8mm, but, I can't get them off. A lot of play. I can't fit a socket in there and my wrenches only go down to 8mm. Might have to hammer a 7mm on there if I can find one.

They are old school 5/16 almost 8mm but not quite the same

I use a ratcheting gearwrench for the ones on the tcase, and sockets for the ones at the axle end

Well that won't work either. It's waay loose. And it's rounded. I just saw a video where the guy said he was using a 6.8mm wrench. I've never heard of that size....

Well, I got the bolts off for the front driveshaft. Had to heat up the bolts and grab them
With some good channel locks. Got the front driveshaft off. Cooked the u-joints. Can't tell if anything was bad now. The cv joint is very tight. A cap came off the ujoint. When I looked inside, it appeared to be missing a single roller bearing. Could have fallen out. Can't find it though.

I now have a much worse problem as well. The motor isn't happy and is now VERY rough to start. So much so it developed a knock. Might not be rolling on its own anytime soon to verify.