Jeep Wrangler Slip Yoke Eliminators Explained

There are two types of joints used on Wrangler's driveshafts, a universal joint (also called a Cardan joint) and double Cardan joints. The problem with a typical universal joint is that it rotates at a varying speed. This causes vibration and wear due to the constant changes in speed. A constant velocity (CV) joint gets its name from maintaining a constant speed while rotating, unlike a conventional Cardan joint. These CV joints come in many different styles however the most common one for Wranglers is a double Cardan joint which is essentially a set of universal joints mounted right next to each other on their own intermediate shaft.

The slip yoke is typically an internal splined shaft that is connected to your driveshaft by means of a universal joint. The purpose of the slip yoke is to transfer power from the transfer case to your driveshaft. It slides in and out of your transfer case allowing it to

change length in response to your Jeep's movements on and off-road.

A slip yoke eliminator (SYE) eliminates the slip yoke from your drivetrain, turning it into a fixed yoke. Why is this beneficial, you might ask? The rear driveshaft of YJ and TJ Wranglers is a fixed length shaft, so installing the slip yoke allows you to change the driveline length in order to account for suspension height changes. 

A slip yoke eliminator kit shortens your transfer case, which then necessitates a longer driveshaft. A longer driveshaft means you'll have a flatter drivetrain angle, reducing vibrations and wear on drivetrain parts if your Jeep has an agressive lift installed. An SYE also provides a slight increase in ground clearance due to the flatter drivetrain angels. With a slip yoke eliminator kit, you don't have to run a transfer case drop either.

Some manufacturers will provide a standard slip yoke eliminator kit as well as a mega short kit, shortening your transfer case even further. These kits include the back half of the transfer case, a splined shaft for the u-joints to mate too, all of the proper output shaft bearings and seals, as well as a speedometer drive gear.

If you install a large lift kit without changing the driveshaft, the first two issues that occur are the driveshaft is now too short, and second, the angles are now too extreme for this kind of joint. When you lift your Wrangler, you are changing your driveline angles. If these angles are not properly set then your Jeep may suffer from driveline vibrations and possibly wear components faster like the u-joints. When the angles become too extreme, joint life will be greatly diminished. Another drawback to slip yokes is if your suspension extends to far it can actually slide out of the transfer case while you are driving/crawling. By installing an SYE you convert the slip yoke to a fixed mounting flange which prevents the risk of your driveshaft from falling out and also allows for a CV driveshaft to be installed.

When the slip yoke slides out too far it runs the risk of falling out of your transfer case. This should never happen with a Wrangler that has not been lifted. If this does happen, not only will you lose power to the rear wheels, but the oil in your transfer case will pour out as well. The reason why CV driveshafts prevent driveline vibrations is they move at a constant velocity unlike a conventional universal joint that constantly accelerates and decelerates as it turns. In addition, CV joints are able to be used at greater angles than u-joints, making them great for lifted vehicles.

Realistically, any kind modifications to your Wrangler's suspension can have negative effects on your driveline. If you are considering installing any suspension lift over 2 inches you should strongly consider installing a SYE and a CV driveshaft. However, you may be able to get away with a transfer case drop for lifts up to 4 inches. After 4 inches its pretty much required to do an SYE and CV driveshaft. The downside to transfer case drops is if you try to drop it too much you may need to change out your engine and transmission mounts to get the right angle, and you lose ground clearance which can somewhat defeat the purpose of a lift kit. Installing an SYE and a CV will help ensure your Wrangler doesn’t experience any driveline vibrations and will keep your driveshaft from being pulled out of the transfer case. 

Rubicon Wranglers are a little better off in that they already have a type of SYE installed from the factory. If you're lifting your Rubicon, the only bit you'll have to worry about acquiring longer driveshafts appropriate to your lift.