This thread is designed for the sole purpose of informing members as to why it is important to put a SYE on your lifted Jeep Wrangler. Now we can answer the “Do I need a SYE” questions by simply pointing people to this thread. I hope this thread will help new members make the right choice when installing a lift on there TJ.
What are Slip Yoke Eliminators and why should they be used?
What is a SYE and why is it used?
SYE stands for Slip Yoke Eliminator. The Slip yoke is the yoke that slides over the output shaft of the transfer case. This is the yoke that the rear driveshaft connects to at the Transfer case.
The SYE kit replaces the stock slip yoke and housing with a sealed housing and a fixed flange or yoke. This fixed flange or yoke is what a new CV style driveshaft will bolt up to. A CV (constant Velocity) shaft uses two U joints instead of a single one and this allows for much steeper angles. These shafts also utilize a two piece design that allows for suspension travel by allowing the shaft itself to compress and extend verses the yoke sliding on the output shaft. The sealed output now also allows for the rear driveshaft to be removed from the vehicle and not allow the transfer case fluid to empty out of the transfer case.
When should a SYE be used?
The stock rear driveshaft is a fixed length unit that relies on the slip yoke to adjust when the suspension travel. When lifting an TJ, the angle between the rear axle pinion and the slip yoke become much greater. The factory setup was not intended for these variations in lift. The angle difference will be most noticeable in the fact the slip yoke will be pulled further out of the housing than before the lift.
The differences in angle can be attributed to several things, but they all revolve around this center point, the length of the rear driveshaft. You will hear various things from various people about what size lift can be ran without a SYE. The key here is to recognize the differences between their TJ and yours.
What are some of the harmful effects of not using a SYE?
The difference in the angles put a strain on the output shaft. This places load on the transfer case bearings and the seals on the output shaft.
Another, more obvious problem, are the U joint ears of the driveshaft making contact with the slip yoke as the driveshaft spins. This will make for a noticeable clanking noise and hard vibration. A transfer case drop will clear that problem up, as well as a high clearance extended slip yoke, but it will not correct the strain on the output shaft.
What are other positives does the use of a SYE provide?
As mentioned before the ability to remove the rear driveshaft if damaged and drive off a trail under the power of the front axle is a major plus. If you run a stock front driveshaft with a SYE, you can carry a spare for both the front and the rear driveshafts.
Hack N/ Tap vs. SYE
There are two different styles of SYE’s out there. There is the HD Slip Yoke Eliminator, and then there is the Hack N’ Tap. The two are relatively different but the end result is going to be relatively the same. With the HD SYE the output shaft inside the transfer case is actually going to be replaced making the SYE the stronger of the two options. With the Hack N’ Tap you actually cut the OEM output shaft then add a flange on it which will then connect to the new CV driveshaft.
In summary, a true SYE is going to be a better option versus the Hack N' Tap. However, if you are on a budget a Hack N' Tap will certainly get the job done.
Rear Shocks
After adding a SYE you may encounter some rear shock issues (especially if you're lifting it over 2 inches). When you rotate the pinion up to match the transfer case output yoke, the lower portion of the shock body may rub on the lower spring perch.
The cheap and easy way to fix it are these Currie CE-9601 Rear Lower Shock Mount Extensions.
The proper way (in my opinion) to fix it, is to relocate your spring perches using something like this. This will of course require a competent welder, but it's really not that hard of a job.
Which SYE do you recommend?
If you're fortunate enough to have the NP241OR Rock-Trac transfer case (only found in the 03-06 TJ and LJ Rubicon models) then you don't need a SYE, since this transfer case already has one from the factory.
If you're like the majority of us however and have the NP231 transfer case as found in all the other TJ and LJ Wrangler models, there are various options in regards to SYE kits, but one of the most popular and well regarded is the Advanced Adapters SYE.
There's certainly a lot of other options out there which I won't even begin to list, but the Advanced Adapters SYE is my favorite.
What if I have an LJ?
Lucky you! The LJ in most cases is fun up to about 4-4.5" of lift without a SYE or double cardan (CV) driveshaft! That's one of the benefits you get from the LJ with it's longer wheel base... much less extreme driveline angles.
What are Slip Yoke Eliminators and why should they be used?
What is a SYE and why is it used?
SYE stands for Slip Yoke Eliminator. The Slip yoke is the yoke that slides over the output shaft of the transfer case. This is the yoke that the rear driveshaft connects to at the Transfer case.
The SYE kit replaces the stock slip yoke and housing with a sealed housing and a fixed flange or yoke. This fixed flange or yoke is what a new CV style driveshaft will bolt up to. A CV (constant Velocity) shaft uses two U joints instead of a single one and this allows for much steeper angles. These shafts also utilize a two piece design that allows for suspension travel by allowing the shaft itself to compress and extend verses the yoke sliding on the output shaft. The sealed output now also allows for the rear driveshaft to be removed from the vehicle and not allow the transfer case fluid to empty out of the transfer case.
When should a SYE be used?
The stock rear driveshaft is a fixed length unit that relies on the slip yoke to adjust when the suspension travel. When lifting an TJ, the angle between the rear axle pinion and the slip yoke become much greater. The factory setup was not intended for these variations in lift. The angle difference will be most noticeable in the fact the slip yoke will be pulled further out of the housing than before the lift.
The differences in angle can be attributed to several things, but they all revolve around this center point, the length of the rear driveshaft. You will hear various things from various people about what size lift can be ran without a SYE. The key here is to recognize the differences between their TJ and yours.
What are some of the harmful effects of not using a SYE?
The difference in the angles put a strain on the output shaft. This places load on the transfer case bearings and the seals on the output shaft.
Another, more obvious problem, are the U joint ears of the driveshaft making contact with the slip yoke as the driveshaft spins. This will make for a noticeable clanking noise and hard vibration. A transfer case drop will clear that problem up, as well as a high clearance extended slip yoke, but it will not correct the strain on the output shaft.
What are other positives does the use of a SYE provide?
As mentioned before the ability to remove the rear driveshaft if damaged and drive off a trail under the power of the front axle is a major plus. If you run a stock front driveshaft with a SYE, you can carry a spare for both the front and the rear driveshafts.
Hack N/ Tap vs. SYE
There are two different styles of SYE’s out there. There is the HD Slip Yoke Eliminator, and then there is the Hack N’ Tap. The two are relatively different but the end result is going to be relatively the same. With the HD SYE the output shaft inside the transfer case is actually going to be replaced making the SYE the stronger of the two options. With the Hack N’ Tap you actually cut the OEM output shaft then add a flange on it which will then connect to the new CV driveshaft.
In summary, a true SYE is going to be a better option versus the Hack N' Tap. However, if you are on a budget a Hack N' Tap will certainly get the job done.
Rear Shocks
After adding a SYE you may encounter some rear shock issues (especially if you're lifting it over 2 inches). When you rotate the pinion up to match the transfer case output yoke, the lower portion of the shock body may rub on the lower spring perch.
The cheap and easy way to fix it are these Currie CE-9601 Rear Lower Shock Mount Extensions.
The proper way (in my opinion) to fix it, is to relocate your spring perches using something like this. This will of course require a competent welder, but it's really not that hard of a job.
Which SYE do you recommend?
If you're fortunate enough to have the NP241OR Rock-Trac transfer case (only found in the 03-06 TJ and LJ Rubicon models) then you don't need a SYE, since this transfer case already has one from the factory.
If you're like the majority of us however and have the NP231 transfer case as found in all the other TJ and LJ Wrangler models, there are various options in regards to SYE kits, but one of the most popular and well regarded is the Advanced Adapters SYE.
There's certainly a lot of other options out there which I won't even begin to list, but the Advanced Adapters SYE is my favorite.
What if I have an LJ?
Lucky you! The LJ in most cases is fun up to about 4-4.5" of lift without a SYE or double cardan (CV) driveshaft! That's one of the benefits you get from the LJ with it's longer wheel base... much less extreme driveline angles.
