98 xj 5 speed 4wd about 200k miles

I was driving home from tonight and it immediately started vibrating while I was driving. I kind of feels like when the u joints in my front axle were bad, but I just replaced them a few months ago. And it stops once I put it into neutral and roll. I've had some issues with the injectors before maybe that's it? Only does it under load.

Any ideas? It's dark so I can't start looking at it tonight, just wanted to see if anyone had ideas on where to start.

Thanks

 

Get under it and check the motor mounts and trans mount. They can get old and crumbly causing the exhaust pipe to drop down on to the trans crossmember.

 

All my mounts seem good. No excessive movement in the motor mounts and no movement in the trans mount

 

Also I noticed that there is a weird thumping sound sometimes when I start to accelerate. Positive it didn't make that sound before the vibrations start

 

Sounds like a mount. Give the jeep and romp on it. See if your shifter moves at all. My 91 would move like 2" cause the motor mount was shot. Just double check it.

 

Lug nuts might be loose?

 

How close is the pipe to the crossmember?

 

The pipe looks like it's where it should be, doesn't look like it's sagging and I don't hear it leaking. But my shifter does move quite a bit when I rev it. I had to just kinda kick the trans to see if it would move but it didn't. My pry bar is at work. So I can't really check the mounts, other then visually. And My girlfriend wouldn't be able to put it in gear and power brake it, without running me over...

 

Peak thru the gap below hood and over dash when hoods open and watch motor for extra movemnet while power braking.

 

I did it, and saw no excessive movement. And if I rev or feather the gas hard, the shifter may move maybe half an inch.
I put it in 4wd today to see if my front propshaft was knocking again, but nothing there.
If it's the drive shaft, wouldn't it be a constant vibration? And that knocking noise is only from a stop and isn't everytime.

 

The jeep is also lifted 3 inches with a tom woods sye and driveshaft.

 

Sounds like exhaust on te crossmember to me. Thats what mine did when I put it in neutral. Check the motor mounts by having someone(you trust) get in and put the jeep in drive while holding the brake. Then have them hold the brake tight while hitting the gas slightly. If you see the engine rise one or both of your mounts is shot.
I would check the trans mount by supporting the trans with a jack and a block of wood under the pan, then drop the crossmember and check if the mount is cracked or worn out
Good luck

 

Can you fit your thumb between the bottom of the pipe and the crossmember?

 

Probably not haha
How much movement am I looking for on the trans mount? I got it in the air today at work, and had my prybar in there and I was able to move it pretty easily and it moved 1/2 to 3/4 of an inch up and down.

Also if it is the trans mount, where can I find a good replacement? I'm having trouble finding one that fits a inline 6 with a 5 speed threw business accounts at work.

 

Bingo!!!!

How do the engine mounts look?