Driveshaft vibration with 2" lift

[ericweissleder]

Driveline vibration with 2" lift

Hi,

I have a 1984 CJ7 with a 2" lift and a new driveshaft - all done by a 4WD shop. After the lift/shaft were installed, I discovered a slight drivetrain vibration. I mentioned this to the shop and got the answer that "vibrations happen" and it'll be very hard to nail down. OK, well last time I go there. The vibration comes on around 35-40 mph, only when under power, and goes away above that. I know it could be anything, but could my pinion angle be slightly off? There are no shims under the rear spring plates... are they needed with a 2" lift? What should the angle be? Is there an acceptable range? To be clear, this isn't akin to a 'death wobble' or anything remotely close—it's more of an annoyance mainly because before those parts were installed, the Jeep didn't vibrate. Any advice is appreciated. Thanks!

 

[mriplaybass]

If you are running a single U joint driveshaft, the differential pinion relative to the transfer case output pinion should be no more than 1° out of parallel. The driveshaft itself should be no more than 15° of slope, and that is pushing it. More than 1° out of parallel, or more than 15° of slope, and you stand a good chance of vibration or worse.

 

[coldair]

If you are running a single U joint driveshaft, the differential pinion relative to the transfer case output pinion should be no more than 1° out of parallel. The driveshaft itself should be no more than 15° of slope, and that is pushing it. More than 1° out of parallel, or more than 15° of slope, and you stand a good chance of vibration or worse.

That is the best way I've ever heard anyone explain it.

 

[mriplaybass]

Thanks! Learned most of it the hard way.

 

[JeeperChris]

Just looking through instructions for a lift kit I'm looking at and this was at the end of it:

LIFT KIT TROUBLESHOOTING

REAR DRIVELINE:
Acceleration vibration: Caused by the pinion being too high in relation to the transfer case output shaft. On leaf sprung vehicles, install axle shims to lower pinion accordingly.

Deceleration vibration: Caused by the pinion being too low in relation to the transfer case output shaft. On leaf sprung vehicles, install axle shims to raise pinion accordingly.

Fixed yoke vibration: Caused by excessive angle at the rear transfer case yoke. Very common on vehicles with 2” or more of lift. Can typically be cured with a transfer case drop kit and shims provided (pinion adjustment may also be required- see acceleration and deceleration vibration troubleshooting above). If this does not cure it, a CV yoke and CV drive shaft may be require. Adjust pinion so it is 2 degrees below parallel with CV drive shaft

 

[ericweissleder]

Thanks for the replies. Very helpful. Next step is to check angles and add shims if needed. Hopefully, that'll do it.

 

[cglax6]

Re: Driveline vibration with 2" lift

If angles are too far off, then you'll need a double-cardan driveshaft. I needed one on mine because my pinion angle is too high. Not sure where my PO scrounged it from, but my angles are pretty extreme.

I had terrible vibration before, but after the new driveshaft, it's almost smooth as butter.

If you use one, geometry will be a little different. The pinion and the driveshaft should be within a degree or two of each other and pointing toward the output yoke on the transfer case. In other words, the pinion and the driveshaft should be lined up and pointed at the TC yoke.

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[jp360cj]

If you are running a single U joint driveshaft, the differential pinion relative to the transfer case output pinion should be no more than 1° out of parallel. The driveshaft itself should be no more than 15° of slope, and that is pushing it. More than 1° out of parallel, or more than 15° of slope, and you stand a good chance of vibration or worse.

Very good and simple explanation here. You shouldn't need a tcase drop or double cardan driveshaft for only 2" of lift.

What lift did you use? How long are your shackles?


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[Lumpy Grits]

Rotate the rear pinion 3*-4* up, with a shim under the axle's spring pads.
You will need a longer spring bolt-
Use steel shims, and not the POS zinc based ones.
NEVER-EVER go back to that shop again!
LG