miglia-spyder

Its coming from the front, and it feels like its under my feet. Its only when i take off from a start, until about 15 mph. It wont happen if i start off slow though. Its not the u-joints or wheel bearings, I changed one wheel bearing and the other was fine, the u-joints are still tight.


right now i have the stock upper control arms on it, and RC X-Flex's on the bottom, do you think the upper control arms could cause this?

djlarroc

Did you check your motor mounts?

Boxer_Bell

I had a similar problem with a vibration only at take off. After searching around, I found (2) broken studs on my transmission mount and a loose bolt that goes through the bell housing into the engine block (the one right above the starter). After I replaced the transmission mount and tightened the transmission bolt back up, the vibration was gone.

XJ's~For~Life

I have a 99XJ Sport and I had Vibration on acceleration also. It turned out to be the Fan had slack in it from a shot bearing.Grab your fan on both sides and see if it has any play in it.

XJ Stryker

Just got done helping a buddy out with this same problem. The Lower Control arms he got from Rubicon Express had faulty bushings.

There are so many thing that it could be your best bet is to have a buddy or your wife/signifcant other move it back and forth while you check everything out. It is really hard to diagnose suspension faults while in your Jeep.

Good luck.

miglia-spyder

Im leaning more towards the motor and trans mounts... I Havent really looked at those at all! I have checked all the bushings in control arm and the RC lowers are fully greased and tight and the upper bushings seem fine too. I mean i cant move the upper control arm by hand at all.

miglia-spyder

Which mount? The one over the cross member?

XJ Stryker

Hmmmm you can't move your mount by hand I hope that is a joke. Well how about a 4500lb vehicle do you think that could move them...

We could not move them either the way we found out was he was moving it back and forth and you could see the Upper bushing of the lower control arms moving. The axle would even pivot a degree or two.

Tranny mount will have vibes in the rear end if it is bad. If the motor mounts are bad you will have vibes in the front. I mean when you crank your engine you will actually see your engine pivot on the Rt mount.

Motor mounts are easy I have a write up in the write up section.

Tranny mount is easy too just make sure you support the T-case with a jack stand or something when you remove the X-member. If you have never changed your mounts I would highly recomend it that way you can rule it out plus the vehicle is getting close to 10 years old.

Boxer_Bell

Yes, the one on the cross member.

96 XJ Sport

Listen to Stryker...I am the buddy that he helped Crawl under there and let someone move it back and forth, apply brakes on and off, take it in and out of gear, put your hand on the exhaust...oh wait, don't do that . I had come up with ways to rationalize all sorts of things being loose until I actually saw it in action. FWIW, my vote is for motor mounts or tranny mount in your case. Good luck.

djlarroc

The guy who sold me my jeep, lied to me and told me it had vibes were from a too short driveshaft. The engine would idle nice, when I drove around the 10-15 mph range, it would vibrate bad. I noticed the engine was leaning to the pass side. And the tranny mount was smashed as well. I replaced the tranny mount (easy) and it was still leaning. I cked the pass motor mount and it was completely off! Guess what? The guy broke all 3 studs in the block! Took me all day to repair, but w/the new mount, all the vibration is gone.

Also, in my research, I have read motor mounts are a problem on the xjs.

miglia-spyder

No i was not talking about moving the mount... I was refering to the bushing in the upper control arm...If the bushing was bad i would think i would be able to feel it with a little arm force.

I will get to replacing the tranny mount! and see if that changes anything!

thanks guys!

XJ Stryker

Good deal. Tranny mount will run ya about 35 bucks from AZ. Be carefull taking the 4 bolts out of the X-member they are prone to snapping. Looks like you live in the rust belt like myself.

I would start by removing the 4 13mm nuts our of the middle of the X-member they are not visible. Well you can see them if you look through the small holes on the x-member. (Make sure you have a support on the T-case). Then remove the 2 nuts and 2 bolts 15mm off the X-member. You X-member will drop. Your tranny will shift a lil that is common. Then you will have 2 19mm or 3/4 inche bolts holding the mount to the tranny. After some cussing and groaning they should break loose.

Good time to clean your X-member. Reinstallation is pretty straight forward from there.

You will have to raise the t-case up a lil higher to get the new mount in place since the old one will have been a lil saggy.

You will also prolly have to pry and wiggle the t-case around some to get the 15mm studs and bolts to line back up. But it will all fit back the way it came down.

Good luck and be careful. Really insure you have a good hold on the t-case prior to dropping the X-member.

miglia-spyder

Great thanks stryker!! I will try and replace that tonight and see if it changes anything...the motor mounts will come when i get a couple free hours next week!

thanks for all the help guys! I will be back with the results!

SeriousOffroad

Before you do anything else, disconnect the front driveshaft from the axle and wrap the caps with some tape so you don't lose. Strap the driveshaft to the heep and go for a ride.

Post up your results please.