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chasing vibes on the highway

8

87baseomatic

NAXJA Forum User
Location
North Jersey
I'm getting vibrations from about 55mph and faster from my jeep.

Run down on the xj. '92 4.0 223k miles, aw4, np242, hp d30, d35. Motor and trans mounts less than a year old. Front spicer ujoints and unit bearings less than a month old. Both driveshafts have fairly new spicer ujoints and have been checked and balanced at the local driveshaft shop. BDS 3" lift with a t-case drop, 30x9.5 bfg at on cragars d windows. Wheels aren't bent and tires balance out perfectly. Tracbar is about a year old and tierods and draglink are under 2 years old. No play found anywhere in the front end or anywhere else on the truck. All the fluids are within a month old and everything looks good in the diffs when I changed them.

If I pull the front driveshaft the vibes go away and the jeep is smooth up til about 80, I haven't tried to go faster. I tried using the front shaft off my fathers 01 xj and the vibes are still there. I put my driveshaft on his xj and no vibes.

Is it possible that its being caused by the transfer case?
 
Check your front pinion/castor angles first!Also check the transfer case front output yoke for play.
 
This is the only argument for a SYE on lifts under 5", that I accept, NO QUESTIONS ASKED. While a TC drop may correct driveline angle in the rear, in the process it worsen the front angles. Do check your front axel pinion angles, get them within spec. If you still have Vibes, loose the TC drop, and either shim the rear axel to correct rear pinion or get a SYE.
 
Just pulled the xj off the aligment rack at my job. Left and right sides specs are: caster is 5.2º and 5.1º, camber is -1.1º and 0.2º and toe is -0.03º and 0.03º. Total toe is 0.00º. My stupid hollow crown automotive tie rod is weak and if you touch it the toe changes the slightest bit.

I can't find the paper with my the angles on the front driveshaft and pinions on d30 and tcase, but put it like this, if I had those measurements in the rear I wouldn't need a tcase drop even.

With the truck in park and the wheels on the ground I can turn the front driveshaft less than a 1/4" so I assume the tcase chain is good. No up and down or side to side movement at all on the front pinion on the tcase. So I guess the bearing is good.

I'm gonna try another front driveshaft from another jeep. My father now tells me he did feel a slight vibration with my front shaft on his truck. Unfortunely two weeks ago I put 1" spacers up front and oem upcountry springs on his xj. The springs havent settled yet and its a 2001 with a lp d30. So I don't know if what he felt was from my driveshaft or from the lift. I know later xj's had issues.
 
You answered all your own questions.While a t-case drop helps with the rear angles it makes the front angles worse.Also your castor is making the angles even worse.
 
Castor is in factory specs though, granted its all the way at one end of the range.

The front driveshaft angles are good though. The angles are much better than the rear driveshaft. Front is very close to parallel from pinion to pinion.

My coworker brought in his xj today. We are gonna swap shafts and see if it makes a difference.
 
Its about a 2 degree difference between the pinion on the d30 and the front output shaft on the tcase. Thats what I mean't by the front being close to parrallel.

All the ujoints are good. Spicer brand less than a year old. The lift in the front is actually 2.5" and a hair over 3" in the rear, I just went out and checked. The software on our new hunter machine called for 0 toe, but now that you mention it, I thought 4x4 xj's called for little toe in. I know the caster isn't optimal. All the tires are balanced. I rechecked them a few days ago.

I'm leaning towards it being a bad shaft. Even though it checked out good at the driveshaft shop. I don't think his balancer compensates for suspension movement, different angles and a lifted jeep.
 
Could it be the rear shaft, vibrations travel. I've been fooled many times. Sounds screwy but a rear driveshaft test, is to load up the vehicle with 5-6 passengers (to change the driveline angle) and go for a drive.
My last troublesome vibration turned out to be a front hub.
New U-joints can heat up and wear out fast if they are installed a little off center (or they forgot the grease at the factory, I've gotten dry U-joints out of the box before, Spicer knock offs often have inferior black or dark grease in them). You really need to whack them with a hammer after installation (before they rust) sometimes to take a little of the stress off of one cap or another.
I had a vibe in a front shaft, which turned out to be excess play in the slip splines. The front shaft has a odd number of U-joints and isn't often a source of vibrations.
If the T-case output shaft bearings are loose they often act like bad pinion bearings and the output shaft will have excessive sideways movement when slapped (on the side) with a plastic mallet. The front T-case seal will often leak when the bearings are going bad.
 
With the front shaft out I have no vibes. Thats with myself and a passenger in the front and also with a vw vr6 engine and trans in the trunk. No vibes with or without the extra load.

All the joints are spicers, I usually add some miltary grade waterproof grease in each cap when I install them. I was always told after you put in joints to wack each end with a hammer to make sure they are seated and to make sure the joint can move without binding or stress.

I had the front shaft rebuild by my local driveshaft guy. He did three new spicers joints and a new spicer centering section, and rebalanced and straightened the shaft. The shaft was slightly bent when I brought it in and the centering ball was very squeaky. I will check to see if the slipyoke in the shaft is loose. I completly forgot about that.

As for the tcase. No excess movement, no leaks. I thought when I put the front shaft back in that it could be a bad frount output shaft bearing in the case but I checked it for play and nothing.
 
87baseomatic said:
Its about a 2 degree difference between the pinion on the d30 and the front output shaft on the tcase. Thats what I mean't by the front being close to parrallel.
Click to expand...
Thats not even possible,nor is it the proper way to set up a CV drive shaft!
 
Since the front has a cv joint at the tcase, the pinion should be pointing directly at the CV joint, not parallel with the output from the tcase.
 
Not sure what do with the truck. I would love to just take out the t-case drop and put a set of shims in the rear leaf packs and see how it drives. Im not sure what size shim I would need. That inch gained back at the tcase would defintly help out the front shaft.

THe lift height isn't even front to back either. Its maybe at most 3/4" lower in the front. I am not sure if raising it with spacers would help at all. With the rust on the truck and the mileage I don't see getting anymore than another season out of it. I don't want to dump money on adjustable control arms or anything as the xj I will get to replace this one when the time comes will get a different treatment liftwise.
 
That front pinion angle is probably your issue - like old_man said. Since you already have vibes, what I'd do is pull the t-case drop out, make sure the front pinion angle is close to 0 again (it's 4-link suspension, so no significant angle change under torque as far as I know... correct me if I'm wrong), then figure out your required shim angle for the rear and fix it. You'll just go from front vibes to rear vibes for a while. At most I see you spending about a hundred bucks on U-bolts and shims, I've seen custom degree shims for $50 before and if you get OEM U-bolts from an aftermarket vendor (my personal favorite is Z&M jeeps, as I can just plug in OEM part numbers on their site and get exactly what I want) they'll run you less than 50. Qtec will cost you about 65 for U-bolts I think.

EDIT: oh, not sure if you put an SYE in the back already. If you didn't it could run you another 100-150 or so if you get a junkyard driveshaft and a 3103-27CV yoke + some grade-8 nuts/bolts.
 
No sye installed.

Just checked, steel shims from rubicon express are pretty cheap. I sell parts at a linc-merc dealer. Our neighbor is a mopar store. U-bolts are pretty cheap there as I pay 25% over cost. It was actually cheaper a few weeks back for me to buy oem upcountry springs from the dealer, than it was to by hd spring backs from quadratec for my fathers xj.
 
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