Vibration under load

[Flivver250]

I am making steady progress with the tired old TJ, correcting past sins. The tires are horribly out of balance I am certain, but I do notice a vibration when you have the vehicle under load, driving down the road with foot on gas. It lessens considerably when you take your foot off the throttle (standard 5 spd). I just replaced the rear u-joints and noticed the u-joints are slightly shorter than the retaining ridge on either end of the pinion yoke. I assume the joint should be a tight fit, there may be as much as a 1/16th of an inch difference. I eyeballed it as close as I could and tightened it down. Can you tell from the picture if I have the correct rear drive shaft? The rig has a 3" suspension lift and a 2" body lift. I will be removing the 2" body lift.

 

[Fouledplugs]

Usually a 3 inch suspension lift requires a SYE (correct way to fix it, $$$) or a dropped tranfercase skid plate.(a bandaid fix, $) Which leads me to believe it’s the angle in which the rear driveshaft is riding under load causing your issue. Also the pinion angle and driveshaft angle might need adjusting if you do run a SYE which requires adjusting the rear control arms.

However having the tires rebalanced by a reputable shop will really help your troubleshooting. As of right now it certainly isnt helping you.

 

[Flivver250]

I will get the tires done soon, and probably will buy a set of 31's as well for regular driving and save the 33's for the desert. What is a SYE?

 

[Jerry Bransford]

Vibrations that start when accelerating and stop when decelerating sounds exactly like the rear axle's pinion angle is a tad too high.

Has anyone done anything to adjust the rear axle's pinion angle?

 

[Flivver250]

I have no idea what has been messed with or altered. I am going to remove the body lift and reassess with the new stock mounts in place. Tires will be balanced and or replaced. I picked up a set of stock rims and will get smaller tires as well.

 

[JMT]

Driveline issue, probably the SYE, Slip Yoke Eliminator. Needed for non-Rubicon’s with >2.5” of Suspension Lift. Replaces your slip yoke at the Transfer Case. Requires correct adjustment of the pinion angle at the rear differential. This is probably your problem.

It’s not your tires or the body lift, though both of those need to be addressed.

 

[Flivver250]

I am sure this is the problem. Would these two items be appropriate for my 2003 Manual tranny?

https://www.amazon.com/gp/product/B000FQ1YUY/?tag=wranglerorg-20

https://www.amazon.com/gp/product/B00B2AEU6W/?tag=wranglerorg-20

 

[JMT]

There are three solutions to driveline vibes caused by a 3" suspension lift

1) Best - SYE and DC (~$600). If you're going to spend almost $600, you might as well go with the BEST. Tom Wood. Been in the business forever and great one on one customer service.

http://www.4xshaft.com

2) Better - a 1" Motor Mount Lift (~$75-170). It may, and probably will, solve your vibes. There are two types. A simple 1" block that fits under your stock motor mounts. A beefy replacement mount.

https://savvyoffroad.com/product/sav-mmltj/

http://browndogindustries.com/Wrangler-TJ.aspx

3) Good - a Transfer Case Drop ($10-50). The most simple way is to buy some washers and stack them 3/4" on each of the six mounts. You'll likely need longer bolts to accommodate the drop. The more expensive route is to buy a transfer case drop from someone like Rough Country. They are just poly spacers.

 

[Flivver250]

JMT, thank you for the thoughtful advice and plan. I am going to remove the 2" body lift and raise the engine 1" and see what happens. It appears the previous owners threw parts at this rig without putting much thought into it. I am having fun making a silk purse out of a sow's ear.