Driveshaft vibration

mathew32008

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Aug 20, 2019
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North Florida
I have a 2.5 lift, transfer case lowered, and additional level for front. Jeep drove great. Back end sat an inch low. So I had a 3.5 inch springs put in the rear. Now sits level and looks good. However I now have bad vibration from driveshaft. I'm wondering if adjustable control arms will cure the problem.
 
No, adjustable length control arms will not cure those vibrations with your factory single-cardan rear driveshaft. The reason being is that your rear axle's pinion angle must remain the same as/parallel to the angle of the transfer case's output shaft.

This is your setup now and you can see how the two are at the same angle.

2joint_angle.jpg


There are three ways to eliminate that vibration. In terms of cost, least costly to most expensive.

1) Drop the transfer case more. Not a good solution.

2) Install a pair of 1" taller motor mount lifts or spacers to lift your engine 1". The effect of that is additive to what your current transfer case drop is doing, both combine to reduce the excessive angle at the driveshaft u-joints caused by your 3.5" lift. Like Savvy's motor mount spacers or Mountain Offroad Enterprises "Bombproof" 1" taller motor mount lift (MML) Kit with rubber (not polyurethane!) bushings.

3) The best method... install a SYE (slip yoke eliminator) into your transfer case and replace the stock single-cardan rear driveshaft with an aftermarket double-cardan (AKA CV) driveshaft. This third choice also requires buying adjustable length rear control arms so the pinion angle can be raised as shown below.

This is the pinion angle required for a DC (aka CV which means Constant Velocity) driveshaft installed with a SYE kit. The rear pinion angle is raised via adjustable length control arms so it points directly up the driveshaft.

CV Driveshaft Angles.gif
 
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No, adjustable length control arms will not cure those vibrations with your factory single-cardan rear driveshaft. The reason being is that your rear axle's pinion angle must remain the same as/parallel to the angle of the transfer case's output shaft.

This is your setup now and you can see how the two are at the same angle.

View attachment 361986

There are three ways to eliminate that vibration. In terms of cost, least costly to most expensive.

1) Drop the transfer case more. Not a good solution.

2) Install a pair of 1" taller motor mount lifts or spacers to lift your engine 1". The effect of that is additive to what your current transfer case drop is doing, both combine to reduce the excessive angle at the driveshaft u-joints caused by your 3.5" lift. Like Savvy's motor mount spacers or Mountain Offroad Enterprises "Bombproof" 1" taller motor mount lift (MML) Kit with rubber (not polyurethane!) bushings.

3) The best method... install a SYE (slip yoke eliminator) into your transfer case and replace the stock single-cardan rear driveshaft with an aftermarket double-cardan (AKA CV) driveshaft. This third choice also requires buying adjustable length rear control arms so the pinion angle can be raised as shown below.

This is the pinion angle required for a DC (aka CV which means Constant Velocity) driveshaft installed with a SYE kit. The rear pinion angle is raised via adjustable length control arms so it points directly up the driveshaft.

View attachment 361987

Is there a kit to get the she kit and driveshaft
 
Is there a kit to get the she kit and driveshaft

It's best to install the SYE and then measure for the driveshaft. There are several SYE'S out there. Some are offered with a driveshaft included but due to the variences from lifts and Jeeps you really want a custom one. If you ever plan on going higher than 4" of lift then get the super short SYE.
TomWoods makes excellent driveshafts and has superb customer service.
https://4xshaft.com/collections/jeep-tj
 
Is there a kit to get the sye kit and driveshaft
Yes, talk with @Shawn at Tom Wood's at www.4xshaft.com and he can provide guidance with their combination SYE and DC (CV) driveshaft packages. You won't find any organization with better pre and post-sales support.

Here's their webpage on how to make that measurement. https://4xshaft.com/blogs/jeep-drive-shaft-tech-articles/measuring-your-jeep-wrangler-tj-driveshafts

Installing the SYE kit slightly increases the space available for the rear driveshaft so it's new length needs to be a little longer than stock. That link and the below photo tells how to measure correctly before installing the SYE so the driveshaft and SYE kit can be ordered together.

Capture.JPG
 
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I experienced the same thing going up 1/2” once- a CV shaft fixed it. Vibes can cause damage - trust Jerry. He always gives sound advice.
 
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