The Official SYE (Slip Yoke Eliminator) Thread *All Read*
The Official SYE (Slip Yoke Eliminator) Thread
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 Cherokee. I have taken it upon myself to talk and question some of the very well respected members of this forum so that we can have sort of a go-too place for SYE related questions. This way we can answer the “Do I need a SYE” questions without actually answering them. I hope this thread will be located in a place for the newer members to easily access it, to help them make the right choice when installing a lift on there XJ. Furthermore I thank all who have helped me during the making of this thread, you are greatly appreciated.
In this write up you will find a couple of things. The numbers represent sections of the write up, almost as a glossary, so easy information can be found.
1. Q & A about SYE’s, what they are, and when they should be used.
2. How To/Technical Aspect Of The SYE
3. Pictures of Stock NP231/NP242, SYE, and Hack N Tap Transfer Cases
4. All available SYE’s and locations that you can purchase them.
Section 1a - Q & A about SYE’s, what they are, and when they should be used.
The Following Was Written By Balloo93, and Used With His Permission (JF Moderator, Member Since 2002)
Balloo93’s Website - http://www.cardomain.com/ride/325707/1 and http://www.cardomain.com/ride/2406854/1
1. 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 84-95 design uses an output housing that contains a seal at the end that holds fluid in the housing and lubes the yoke as it skids on the output shaft. This fluid is the Transfer Case fluid. The 96 and later models use a sealed housing and the yoke is lubed with grease from the factory. A small rubber boot is attached to the housing and the yoke to keep the grease from contaminants. The downside is that this setup is longer from the rear of the case to the end of the yoke.
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 (84-95 transfer cases).
2. 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 XJ, 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 XJ and yours.
The worst possible setup you can have is a 96+ with an auto transmission, a NP242 transfer case, and an 8.25 rear axle. This combo makes for a long drivetrain and the 8.25 pinion housing is also quite long. These factors will leave you with a short rear driveshaft and even a 2" lift will see negative affects from it.
The best setup for less noticeable vibration would be a 84-95 with a manual trans, a NP231 transfer case and a D35 rear axle. The 84-95 slip yoke was shorter than the 96+. The Manual transmissions are shorter than the auto transmissions. The NP231 is shorter than a NP242 transfer case. The D35 has the shortest pinion housing, followed by the D44 and the longest is the 8.25.
3. 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. The 84-95 slip yoke housing is more prone to showing obvious signs by leaking transfer case fluid.
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.
4. What are other misc. 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.
5. Which SYE/Driveshaft combo do you recommend?
There are several different configurations for a NP231 transfer case, but only one or two for the NP207 and NP242. These options are both offered from Rubicon Express in the form of their Hack and Tap SYE. It requires you to cut the rear output shaft down to 1" and tap the end so that a flange can be slid over the splines and bolted to the output shaft. The 96+ H-n-T kits for the NP242 are much cheaper than the older style ones. The reason behind this is that the older units have a flange and a housing that must be fitted. The 96+ are sealed housings, so it only requires the flange.
The NP231 offerings are plentiful. There are a couple of flange style Hack and tap designs (RE and Currie) and even more with a shorter and tapped output shaft that use a yoke or flange. There are also Heavy Duty units that use a 32pline output shaft and a Yoke. The replacement output shaft types are more involved as far as installing them, but they also allow the easy use of a stock front driveshaft to work.
A stock front driveshaft from a 91+ auto transmission and NP231 equipped XJ can be used with either style SYE. The flange style setup will require an adapter to work, but most yoke style SYE use the same 1310 U joint that the front shafts use stock. This setup can be used for lifts ranging from 3-6" depending on which type of SYE you use. The yoke style SYE's tend to be shorter than the flange and adapter type, so a taller lift may not be possible since the stock shaft has only so much travel to it. The longer type SYE can use a stock driveshaft with more length.
Section 1b - Q & A about SYE’s, what they are, and when they should be used.
The following excerpt is from High-Performance Jeep Cherokee XJ Builder's Guide written by Eric Zappe, and used with his permission. He is also a JF Moderator (username EricsXJ) and member since 2001. For more info on this book or Eric's cherokee, visit www.ericsxj.com
"Lifting a Cherokee results in steeper driveshaft angles that can sometimes lead to driveline vibration. Some XJs are more prone to vibration than others and there's no way to know for certain if you'll get them until it's actually lifted. '96 and newer XJs are more prone to vibration than older ones due to a change that Jeep made to the slip yoke. Pre-'96 XJs have an extension housing on the back of the transfer case that encloses the slip yoke. This housing offers more support to the transfer case output shaft and is less likely to develop vibration at smaller lift heights. The '96 and newer XJs do not have the extension housing which means less support for the shaft. This makes them more sensitive to steeper driveshaft angles and some newer XJs develop vibration with as little as 3 inches of lift. Some lift kits include a transfer case drop to lessen the driveline angle, but this is really just a cheap band-aid fix that may or may not work. Besides, why give up clearance by lowering the transfer case just after lifting the Jeep to gain clearance? The real solution is a slip yoke eliminator kit, or SYE for short, and also referred to as a fixed yoke conversion or short shaft kit.
A heavy-duty SYE kit replaces the stock output shaft with a thicker and shorter output shaft with either a fixed yoke or driveshaft flange. Having a shorter output shaft also means the distance between the yoke or flange and the rear differential is increased which will lessen the angle of the driveshaft. But also, the yoke or flange will be closer to the bearing that supports the shaft. This results in not only less vibration, but less stress on the output shaft bearing. Advance Adapters, JB Conversions, Rubicon Express, and others, offer HD SYE kits for the NP231. Installation can be done without removing the transfer case from the Jeep, but some prefer to remove it to make the SYE kit easier to install.
Not only does Rubicon Express offer a HD SYE, but they also make a different version of SYE that doesn't require you to open the transfer case to swap the shaft. This kit, affectionately called the "hack-n-tap", is done by cutting the stock output shaft to shorten it, drilling a hole in the center of it, and tapping threads so that a driveshaft flange can be bolted on. As long as its installed properly, the "hack-n-tap" SYE will work well. Even though it may not be as strong as a HD SYE kit, the "hack-n-tap" is still stronger than the stock driveline. The "hack-n-tap" is a good low-cost alternative for '96 and newer XJs as its roughly $150 cheaper than a HD SYE. However, if you have a pre-'96 XJ, the cost savings is minimal so it might be better just to go with the HD kit instead. If you have the NP242 transfer case, there are less available SYE kits to choose from, so the "hack-n-tap" is a good option for you as well. Don't forget - with any SYE kit, you'll need a new CV driveshaft to go with it."
Section 2 - How To/Technical Aspect Of The SYE
As we have already learned 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. If you are going to use the front CV driveshaft out of an XJ you will need Spicer part number 211229x or Precision part number 627 which will be used to attach the CV driveshaft to the flange.
The two main transfer cases that were used during the XJ production were the NP231 and the NP 242. The NP 231 has many more SYE options then the NP 242 because with the NP 242 you basically are limited to the Hack N’ Tap style of SYE’s (unless you homebrew a SYE). Here are a few links which provide directions on the installation of both the SYE and the Hack N’ Tap style for the NP 231 and the NP 242 transfer cases. These links can also be found in our XJ FAQ section which is stickied at the top of the Cherokee Technical Forums
NP231 Replacement output shaft type SYE
NP 231/NP 242 Hack and Tap style SYE and DIY hack and tap SYE:
NP 242 - http://polytropia.com/cherokee/sye/
NP 231 - http://www.dpgoffroad.com/tech/rubiconsye.htm
DIY Hack N’ Tap - http://www.4x4getaways.com/oldmansye.htm
The following is a video of a SYE installation on a NP231 TC where the output shaft has been replaced.
Custom SYE Conversion for NP242 applications
Section 3 - Pictures of Stock NP231/ NP242, SYE, and Hack N Tap Transfer Cases
Pre 96 NP231
Pre 96 NP242
Post 96 NP231
Post 96 NP242
Slip Yoke Eliminator
Hack N Tap
Section 4 - All available SYE’s and locations that you can purchase them
Rubicon Express SYE’s
HD SYE Kit (NP231)
Heavy-duty SYE/CV driveshaft combo (NP231)
1807 SYE KIT CV TJ/XJ 96+ *Hack N’ Tap* (NP231/ NP242)
1801 SYE KIT CV TJ/XJ Pre 96 *Hack N’ Tap* (NP231/ NP242)
SYE/CV driveshaft combo *Hack N’ Tap* TJ/XJ 96+
HD SYE Kit (NP231)
Hack N’ Tap Pre 96 (NP231/ NP242)
JB Conversions SYE’s
HD SYE Kit (NP231)
I would like to thank a few people for making this thread possible
EricsXJ – Thank you for allowing me to use material out of your book, I am also very grateful for having your help in preparing this write-up. You have also have supplied me with suggestions and constructive criticism which have ultimately made this thread that much better. This thread would have been extremely harder for me to make without your expert help, and again I couldn’t thank you enough.
Balloo93 – Thank you for your participation in this thread, I can tell that you spent a long time preparing and writing your responses to the questions that I had asked you and there aren’t words for how grateful that I am for the time that you spent working on this thread. I would also like to thank you for your suggestions and ideas for my thread which have greatly changed the way this thread has turned out for the better.
Jason, aka: Jeepin.com – Thank you for your excellent knowledge on jeeps, you may not know how much you have helped me as I never directly had asked you for help but through the research that I have put into this thread I have used a lot of what you have said regarding SYE’s and driveshafts help me with this write-up. I would also like to thank you for allowing me to use a picture of your jeep in this thread.
Sharpie – You have helped me all along the way and I thank you for the knowledge that you have given to me outside of this forum. Without it I would have had a very hard time with this write-up.
1990JEEPXJ – Thank you for allowing me to use a picture of your jeep in this write-up it is much appreciated.
black2door - Thank you for allowing me to use a picture of your jeep in this write-up it is much appreciated.
wojtizzlator - Thank you for allowing me to use a picture of your jeep in this write-up it is much appreciated.
Man............bored at work today???
Good Job KYLE!
but thanks, and i hope this thread will help
Awesome right up Kyle.
Thanks for the great information!
You deserve a :trophy1:
holy god you're bored :rofl:
evidently, the castle nuts needed to be tightened down not to 35 ft lbs, but more like 100 ft lbs, which is bad. That's the only way I got the cotter pins in. I think I'm gonna get some thinner ones.
Post 96 NP242 pic doesn't work.
Good job :2thumbsup:
dopod thanks, and fixed.
when i get home today i will add that 242 image, i guess i forgot to put it in.
brian - ya grab some thinner cotterpins, and actually i have some extras in my spare hardware box in my jeep. If you want them there yours. Also if you want to wrench this afternoon i would be down. Just let me know.
excellent post, and hopefully newbies find it :)
nice tires----i mean...Post! haha
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