Guest article by Dean Settle, aka 'Dillinger'. Contents and opinions are the author's own but are pretty much "on the mark".
Minor editing to fit new site format.

Introduction by the author:

AZ Driveline's kit doesn't address the very thing you should be after in a SYE kit. It should be a priority to REDUCE the DRIVELINE LENGTH from the output bearing on the transfer case. Therefore, you waste money when the rear bearing has to deal with more stress than just the weight of the universal joint back there. Now it's got to deal with a yoke, as well as 2 universal joints and a flange...

Can you say new transfer case at 50,000 miles? Ever seen one of these suckers sieze at 60 mph?

PLEASE READ this before attempting things to fix vibrations!!! It is very important that you understand the forces that are working on your driveline and address them CORRECTLY, and spend the minimum amount to do so.


The mechanics of the Cherokee transfer case as applied in lifted vehicles

If it's been said once, it's been said a million times : The 231 and 242 case outputs on ANY XJ out there is not intended to operate a drive shaft angle of more than 7 to 8 degrees.... with the stock slip yoke in place.

New guys will repeatedly try to "get by" without spending the coin on a reputable solution to the problem. Would they spend $10 dollars on a set of "quality" wrenches? You get what you pay for...and those other fixes will only chip away from your hard earned money that will eventually purchase a Slip Yoke Eliminator kit of some description. This article is an attempt to save your money for the tried and true fix for the problem, as well as a basic mechanical education that attempts to explain what's happening down there.

I was once forced to deal with this problem. I was at the point of determining what would work, and more importantly...what wouldn't. I disassembled the transfer case that I had just blown apart on a 1987 model with six inches of lift. There was no warning... there were no "vibes". It just seized because of the increased stress of runout had been scoring the rear bearings into their track. I replaced the case (it was completely demolished and chunks of aluminum were EVERYWHERE ) and really looked at the attributes of the transfer case output shaft design in detail for the first time. Investigating Tom Wood's SYE kit, I determined that it did place the first universal joint very close to the bearing. This introduced a limiting force (the bearing) directly at the end of the shaft, instead of many inches from it.This stopped the runout and oscillation forces cold in their tracks. All of the cheap "solutions" were also investigated, and my investigation into several cases that were subjected to these "cures" were combed through....with the following discoveries.....

A.)There is the " Transfercase drop/slop" solution.


B.)There is the "long slip yoke/joke"....

Runout of the shaft behind the bearing can only be addressed with a SYE kit that shortens the output shaft length. Why would one attempt to lengthen an already too long mainshaft, and place the universal joint even further from it's only controlling point?

Photo added to article to illustrate author's point.

This photo of a long yoke on a lifted XJ shows how much further the yoke sits on the transfer case output shaft . You can see where the shiny area that is now exposed which indicates this yoke is riding about 1 1/4" further out than before.
Photo is not original to article and was added to further illustrate the author's point.

C.) Why get a SYE?

Do not be fooled that you cannot feel any vibrations, and therefore believe that you do not need a SYE kit. Not having vibrations means ' Jack' in a lifted truck. THEY ARE JUST THE VERY NOTICABLE SIDE EFFECTS OF INCREASED RUNOUT. Runout of the shaft behind the bearing can only be addressed with a SYE kit that shortens the output shaft length and controls runout and oscillation of that shaft..

Even if you raised your vehicle 2" , this will update the rear output to a more pliable double cardan, as well as move the first universal joint in the new shaft closer to the output bearing in the case. Runout of the shaft behind the bearing can only be addressed with a SYE kit that shortens the output shaft length. It has been noted by several sources that newer Cherokees with the "new" design were delivered from the factory (and actually made it to the showroom floor) with vibrations. This indicates that the later model design is probably even more supceptible to runout and oscillation in "stock" form. Lifting will only exacerbate the problem.

Buy the SYE kit if you've lifted the truck anywhere near 2". This goes for the older models as well. If it ain't stock, you've bypassed the optimum angles for a slip yoke. Trying to get by without the purchase is going to cost you a transfer case output bearing sooner or later....hope you're not traveling at 60 mph when it seizes.....

Any mechanically inclined individual can understand what is going on, once they look at the situation.

The factory...yes , even early models are fine at static height as delivered..... It's when the driveshaft angle creeps steeper that the problems evolve. Look at the lone bearing at the output shaft ...

It's so far back from the end of the shaft in the picture, it can't begin to address the runout that occurs on an unregulated shaft that far from it's only controlling force. Every other force acting on the shaft/slip yoke union is introducing havoc and uncontrolable input.....all given from road/spring input, acceleration, compression braking, etc....

The least you can do is push the first universal joint in the equation back as close as is physically possible to the lone bit of controlling force on it. This will stop the runout that the drivelines movements are introducing. It will force the rubber bushing on the crossmember to actually do it's job, and allow the whole transfer case to move instead of the shaft union clearances taking all of the abuse.

HACK jobs.... (Hack & Tap SYE's)

The hack kit is technically a SYE. It eliminates length from the rear output shaft. This is the main defining characteristic and duty of any good SYE kit. You will still need to purchase a rear driveshaft with a double cardan design with this kit.

Whether you get Tom Woods to build a whole kit for $400 dollars(after your $200 core is returned) that includes the driveshaft already cut to measure (you give the length to Tom) or a hack job that requires you to supply the machinists part and a driveshaft to boot...... They both address the runout problem.

You're not done yet....

The Double Cardan joint driveshaft ( supplied from Tom Woods, or your choice of shop) will need shims to raise the rear pinion into the driveshaft's new angle requirements. Unlike your stock set up, the SYE shaft will require that the rear driveshaft be aimed directly at the output of the transfer case. The increments in these shims vary from 1 degree to 8 degrees on the far side. You'll need to aquire an angle finder from any building supply , such as Home Depot or Lowe's.
At the pinion, with the rear driveshaft removed, place the anglefinder against the two lips of the pinion flange. This should give you a reading. Note it and remount the driveshaft. Now place the angle against the driveshaft. This will give you another reading. Subtract the high number from the low one, halve this number...and this is what you need in shims to align the driveshaft tube with the rear of the transfercase SYE flange. Remember to allow for one degree down. This gives you room for axle wrap on acceleration, which lifts the pinion, and still doesn't get into axle pinion drop...which occurs on braking and compression braking.

Good luck on your installation. You're on your way to understanding the forces that play havoc on your driveline in a lifted (no matter how little) truck.

Thanks again to 'Dillinger' for allowing me to post his research for everyone's benefit. Was Dean's former website but is currently a dead link. You can vist a copy of the site using the "Internet Wayback Machine" as described on the downloads page.

If you have pics of your own repairs or can suggest other methods - please contribute your ideas (and pictures) to this article!

Revised on: November 21, 2006

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