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.
SLIP YOKE ELIMINATORS
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.
TRANSFER CASE DROPS ONLY EFFECT THE ENGAGEMENT OF THE 4WD CLUSTERS AND WEAR INSIDE OF THE TRANSFER CASE. THEY ARE SELDOM AND HARD TO GET RE-ADJUSTED PROPERLY TO AVOID THIS WEAR. Add to this the fact that you just raised your vehicle. Now you'd like to LOWER a portion of it?
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? 
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.
http://www.widowmakeronline.homestead.com 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!
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Revised on:
November 21, 2006 |
