I've got a vibration that starts at low speed (20 mph) and increases with speed and never goes away. It is not a minor annoyance...there is something wrong and I need to find it.

The tires/wheels are well-balanced and the rear DS U-joints seem tight.

Queston #1: Any other suggestions on the likely source?
Question #2: Could I be missing something in the U-joints - like not testing them correctly for play? I crawled under the other day and twisted by hand and found zero movement.

 

sure its a drive line vibe not motor

 

No...but I can't imagine what could vibe like that in the motor...it's smooth as silk at any rpm in neutral/park.

 

bent drive shaft bent axle bent rim busted cord in tire did you check these things also

 

Do your u joints have full range of motion? Meaning do they bind at all? If you pluck the driveshaft out, your joints should move easily through out their range.

 

I have not pulled the DS...plan to but don't want to pull it twice (time is tight...winter is coming, wood to chop). If I've got bad U-joints, I'll buy them and do it all at once.

Rims are in excellent shape - American Racing Outlaws - and tires are excellent - new GY RT/s with no popped belts/cords. Vibe is the same with two different sets of wheels/tires. I changed out the original set in part because I was searching for this vibe. Sold those on C-list, bought these from a friend.

Bent axle? Hmmmm. How do I check that?

 

I plan to...but by the time I have it jacked up on stands and my wrenches in hand and the DS out, I might as well install new U-joints or a new DS. Is there any easy way to diagnose before I get the jack out?

 

have some one follow you check for wheel wobbles jack up rear of xj put on jack stands put in gera see if drive shaft wobbles is the balance weight still on shaft

 

Look at your driveshaft. There are little peices of metal like welded or somehow glued onto the shaft the size of a dime and two or 3 dimes high. If you see NONE but a white spot where something else was on there your missing balance weights..

I would balance the driveshaft or look for dents, bends etc.. Also, at 20Mph is a spot where the harmonic balancer starts to wobble when tolerances start to go out on it.. Its the pully looking thing by the serpantine belt near A/C bracket.. See if wobbling or belt looks like its bouncing a lot or something. You can see Im a real tech LOL

 

I've changed out harmonic balancers before - wouldn't that part vibrate at high RPM while in neutral?

 

I have no idea.. I see all kinds of post on harmonic balancers going out.. I would check that, drivesharft, u joints and axels.. If it builds up and gets worse while driving somehting is loose or out of balance... If it comes and goes thats another story..

 

 

I'd get the rear axle off the ground, leave it in 2wd, & run it through the gears. If it shakes, you've at least isolated it to the rear half of the drive line. If it doesn't, it's in the front.

You could also pull the wheels & do the same thing to further confirm it's in the driveline.

 

The easiest way is to pull the shaft out.