Hi. New here.

2000 Jeep Cherokee XJ 4.0 auto.
3.5 zone lift with Bilstein shocks
Adams rear Drive shaft and SYE kit.
137k miles on the Jeep.
31 inch BFG km3 tires
I have owned it for 2 months.
everything has under 500 miles so far
Took the jeep in to a local shop to have it Regeared from 3.55 to 4.11 to accommodate the tires.
Had a spartan LSD installed in the front
new rear carrier in the rear and all new bearings at the carriers and the wheels to basically rebuild the axle.
I picked it up last Thursday and drove 18 miles home just cruising on the streets 40ish max.
Been driving it around town the last few days and finally hit the 100 mile mark on the gears. So today I took it on the freeway and I have a good vibration from 55 mph upwards. I only got to about 67 and backed it down. Only went on the freeway about 2 miles. The vibrations only occur while accelerating and go away when I let off the gas or barely touch the gas maintaining speed.
Before the regear I did the SYE kit and I had no vibrations all the way up to 80mph. Not one it was smooth.
the pinion angle is currently at 1.5 below the driveshaft and since I had no vibrations when I installed the SYE I felt it was in a good spot.
Today I removed the front drive shaft and moved the rear drive shaft ujoint at the axle 180 degrees to see if that would do anything and nothing changed.
Am I chasing my tail thinkiing it might be pinion angle when its within the 1-3 degrees below the driveshaft angle as called out by Adams? Should I talk to the shop about the vibration? Any input is appreciated. Thanks

 

Consider two (or more) things can coincidentaly happen.

is it really driveline vibes, not wheel vibes? Wheel vibration will be 4.11 times (Differential gear ratio) slower than drive shaft vibes in your case. Maybe you lost a wheel weight? Maybe a wheel lug is loose? So make sure it is not that. I assume this is in rearwheel drive. Is your front drive shaft spinning (i.e. you have unlocked, disconnected hubs?) If hubs unlocked, AND not in front drive, that eliminates the front drive shaft as the culprit, as it wont be spinning.
.
Jack it up and inspect, any dents or missing weights on the drive shafts, are all the bolts in place, nuts tight?

I dont see a mechanism where a ring and pinion replacement failure, short of catastrophic pinion bearing failure, can cause driveline vibes. Youd see chunks of metal in the diff oil if that happened, plus an oil leak at pinion! ( have you changed the diff oil, right? If you havent already, install a drain plug, with a magnet, easy to drill and tap for a 1/4 pile tap. At the very least add a magnetic fill plug, even that can help)

Now the reassembly from a ring and pinion repair or change that is another matter.....
Other than handling damage, damage like a dent or a weight getting knocked off the shaft, there is also clocking of a drive shaft...

How the Ujoint is clocked is sometimes, very important for vibration. Each end of the U joint has four possible positions to be clocked on the end flanges to the respective diff or transfer case flange, so there are 4 x 4 possible ways to bolt the shaft to the two flanges That is 16 different mounting posibilities! That is why you are supposed to mark them prior to taking them apart.

So first thing.. confirm it is really a driveline verses wheel vibe, or really a wheel vibe.



good luck.

 

I considered the wheels and tires even though they only have 210 miles on then so I bolted up my wifes set from her Cherokee but they are goodyear assurance tires and I have the exact same vibration. I dont see how it could be the gears either but possibly the rear pinion shaft?
The SYE and rear driveshaft are new as well with only about 220 miles on them also. Im going to check the yoke run out on the rear axle and see if there is any deviation. Im aware of the phazing of the u-joints and the shaft is correctly put together as the yoke ends match on the main shaft before the double carden. Ill keep at it and see what the problem ultimately is. Thanks for the input.

 

I would suggest taking the rear of the driveline loose and clocking it 180°

 

Did that and removed the front driveline.

 

Check your motor, Trans, & tcase mounts

 

Take the rear driveshaft out and drive it in 4wd and see if the problem goes away.

 

they were replaced with new Mopar ones

 

Ill give that a try but with removing the front already and nothing changed I have Isolated the problem to the rear. Checking the run out today of the 2 rear yokes and the drive shaft. Thanks

 

Given the shaft is new and thus could not be clocked to anything, if you move the clocking of it now, you could see a change in vibration. ( better or worse!) oh that is the pessimist in me. keep in mind there are 16 variations to try to find the "best", and even the "best" may still deliver unacceptable vibration, say if the shaft itself is too out of balance, even clocking can't fix a large shaft imbalance. You can give it three tries, move it 180, then 90 to one side of and the other side of that, the thing is you can also have end to end induced vibration, so then you can try moving one end of the shaft 180, but leave the other end of the shaft where it is, as this too can influence vibration. You need to decide when to stop or keep fishing! But then again, the shaft might be so wonky that this whole exercise of clocking is futile.

If it was the old shaft being reinstalled, and it wasn't damaged, well yeah it may only had been clocked wrong, and there may be several of those 16 position that will give vibration free service. If you go this route, paint mark all four flanges as a starting point reference, and take careful notes, and test drive, a tedious process, but hey maybe you will get lucky first try and vibe will be gone.

You may find a balancing place is the only solution for you. but there are a few things you can inspect or try on your own without balancing equipment. But sometimes you need the tools,and expertise or a good balance shop.

Id hear stories all about balance from my Dad as a kid, as he ran a spin balance machine for helicopter blades, turbines, and even whole missiles, they all were spun on it... . It can be intense mathematically and scientifically. Cool equipment They could spin something around a bit, and tell you exactly where to put a certain sized weight, and your done! I saw the machine a few times. This was way back in the 70s. I'm purdy sure that the equipment is much more better now with computers and such. There was a lot of big ole computer stuff on that machine, it was huge, armored screen around it area to catch debris if something got loose, double keys required on a huge steel console to operate it. I recall it was hydraulically driven, big hoses on the ground going to it. Big crane to set things on the spin machine. Missiles were balanced standing up. I guess some things will sag if laid on their side for balance.

 

This afternoon Ill be doing the runout test on all 3 parts. Then Ill mount up my gopro and see what the axle wrap looks like under load to see if Im possibly wrapping too much causing the pinion and driveshaft to missalign too much. Once I have the results from these tests Ill report back. I also made an appointment with the shop and the vibration next week for them to check it out as well if I cant find the problem area. Thanks

 

If your drive shaft has a worn out Double Cardan that could be the culprit. I know you said it's brand new, but........? Hope it isn't inside your new gears/pumpkin? Good luck!

 

Ok but If you remove the rear driveshaft and the problem goes away then it is most likely in your rear driveshaft. If it doesn't then it is something in your rear axle.

 

Update:
runout on both yokes and driveshaft was perfect.
Took video of the resr axle/drive shaft and under load it looks like my axle wrap brings is too -1 to -2 pinion angle.
Had the shop recheck my rear gear and axle set up. They went thought it and everything looks perfect and the preloads are set correctly. They suggested having the rear shaft checked for balance and sometimes the increase in driveline speed from the gear change can highlight a slight balance issue.
Im going to pull the new Adams shaft and have the balance checked. While its out Ill drive it with just the front shaft and see how it feels. If nothing comes of that then Ill install a new rear pinion angle shim to 2.5 and see what that does. Thank for the suggestions.

 

Could it be death wobble? Just saying. They had to have tie rod and track bar out to get into the front diff. Maybe a wollered out track bar bolt holeo bad bushing. Maybe something work checking. Good luck.
PS what's the going rate for regearing with a LSD in 2021?

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