Vibes after regearing

Yesterday I picked up my newly regeared XJ (3.07 to 4:11). I have vibrations after 60mph. It has no SYE/6.5 RC lift/ D30 & 8.25 (welded)/33 KM2's. It had a slight vibes over 60mph before the regearing. A ujoint was replaced in the rear d-shaft as well. Gear set up incorrectly?

Two things that could cause vibes.
Have you correctly set the rear axle u-joint angles using shims?
A 6.5" lift probably requires a SYE to get acceptable u-joint angles.
The front yoke angle also needs to be correct, along with the alignment.
Your drive shafts are now spinning much faster at 60 MPH and any previously existing vibes, possibly unnoticed, have been greatly increased.
Time for the fine tuning.
http://www.4xshaft.com/index.html

Could be a number of things,first off you increased your driveshaft RPM's.Second,since you have a 8.25 what brand gears did you purchase?Third,at that lift you really need a SYE kit!

LazyXJ: Thanks for the idea on the faster d-shaft spinning. I should have figured that :doh: .

RPCphx: I have had the lift in for 2+years and about 15000miles. It never had vibes until past 60 mph and even then were very slight. My commute is max speeds of 50mph and therefore was never an issue. The gears are "Motive" IIRC. I bought an SYE kit when I put in the lift and since there were no shakes, I just never got around to putting it in.

Thanks for the quick reply and info folks

nonnie said:

I bought an SYE kit when I put in the lift and since there were no shakes, I just never got around to putting it in.

Click to expand...

Looks like you have a project for the weekend.
The SYE only take a couple of hours to install if all goes right.
You will probably need to shim the rear axle so make sure you have a source. I would imagine it will be around 6 degrees, assuming that the spring perches are in the stock position.
Do you already have a CV drive shaft?

I have a front d-shaft from an AW4'd XJ. Sourced that it sould work. I'm heading out in the morning for a 4 day JEEP run. The XJ will be on the trailer for all 300miles (one way) to the run. SYE will have to wait for a week or so.