Folks,
my jeep has always done this but I don't think it should. If I'm driving in 2WD I can rev at full throttle to the redline and everything is fine. If I do the same in 4FT I get a vibration from the floor at about 3500rpm or higher. It starts as a rumble and builds towards the redline to a vibration you can feel on the floor.
I can't _see_ anything obvious but where should I be looking, and should I be using a bar or something to check for movement?

Thanks!

edit: 1997 4.0 Auto with 242 TC. Stock suspension apart from HD rear springs. 235/75/15 tyres on stock alloys.

 

Hello,
Did you ever figure this out? I am having the exact same issue . . .

 

Any play in the front driveshaft or u-joints?

 

Nope - none. I replaced all u-joints in front and rear drive shafts and had them balanced. Other background info:
- 3.5" RE lift, sye, rear leaf spring relocation brackets for better shackle angle, 31" tires, diff fluids changed, TC fluid changed. Trans mount is tight.

The thing is, this didn't start until after I did the rear relocation brackets (FST no-lift brackets) for the leaf springs. IT only happens in 4WD - feel like it is in the front. The rear (2WD) is super smooth. Running stock shackles.

 

Are they the orginal shackles or stock replacement?

 

stock replacement

 

Driveshaft angles have changed. Might need a transfer case drop from what ive been reading elsewhere. Every XJ is different.

 

That doesn't really seem right. I didn't have the vibe before improving the rear. Adding the relocation brackets lowered the rear = improving angles. Any other ideas?

 

I'd say there is wear in the front driveshaft slip joint spline that's making the middle of it spin off center under load. Just my opinion.

 

Ummm, no. Front drive shaft is CV/double-cardon drive shaft . . . . Rear is .SYE. Appreciate the opinion though.

 

Okay, that being said, it's possible the CV is bottomed. It has a limited amount it can move and it may be bottoming out against the end plate. You can adjust the length a little at the spline in the center of the shaft by loosening the locking collar and collapsing it just a little.

 

Suprise reply! Lol.

No, it still happens a tiny amount but it's a lot better since I greased all the zerks. It has also had a new rear axle since this post which helped too. I don't think it was just the one fault but a few worn parts combined. I certainly didn't find a "magic bullet" solution. Sorry.

 

Interesting! Never considered that. Will look into it.

Thanks

 

All good. It is the first time I have gone into 4-hi in a while, maybe need to grease. Sounds like I will be on my back again this weekend. Appreciate the input!

 

Hello Scottiem303,
If you're not able to determine a solution based on suggestions from fellow forum members and you decide to address this with your dealer, please let us know via private message. We would be more than happy to provide you with an additional layer of assistance for that process.
Laura
JeepCares