I Hate Worms
stock drive shaft angle just doesn't cut it anymore once you
lift your Wrangler.
really can do the SYE kit in your own garage and save some
bucks. As far as mechanical modifcations go on a Jeep, it's
actually one of the easier ones to do. You may need a buddy
to help you with removal and moving the transfer case.
JB Conversions NP231 output shaft (top) and stock shaft (bottom)
are quite different on the outside end (on right). The new
shaft is much fatter, has a higher spline count, and is several
inches shorter than the stock one. Which would you rather
If you read
the Superlift Rock
Runner suspension article you know exactly what I am talking
about. Any time you make a modification to your Jeep you open a can
of worms. A suspension install can bring about a lot of worms. Two
of the biggest worms you will encounter are a change in gear ratio
and driveline vibrations. The one we are going to address here is
the driveline vibration problem. Since not all of us are mechanics
or engineers, I think the first thing we should do is define the problem.
Once we have done that we can talk about the solutions and, of course,
how JB Conversions
and Tom Wood's Custom
Drive Shafts helped us solve them.
of the greatest problems with Jeep Wranglers is a short rear drive
shaft. The combination of a short wheelbase and a long driveline
(engine, transmission, transfer case) makes for a very short rear
drive shaft. This is not much of a problem when the Jeep is at stock
height. The back of the transfer case and the front of the rear
differential are pretty close to the same height. This means that
the drive shaft itself does not need to have much of a slope. This
lack of slope allows for the u-joints at each end of the drive shaft
to move freely and without causing any vibrations.
When you lift
the Jeep to gain ground clearance, you move the tail end of the
transfer case up and away from the rear axle. This causes the operating
angle to be steeper, which in turn causes a binding effect on the
u-joints at the ends of the drive shaft, leading to vibration. The
extent of this effect can vary from Jeep to Jeep. Some may only
have a small annoying vibe, but even a little vibration can wear
out u-joints in a hurry. The effect gets much worse off-road as
your suspension flexes even farther away from the transfer case.
Broken u-joints, drive shafts and transfer cases could result in
vibrations in a Jeep are like little gremlins. It is easy to dismiss
the importance of a smooth-running rig. Since most of us Jeep owners
fancy ourselves as rugged individuals with Jeeps, we also tend to
come up with excuses for the vibes. We say things like "It's
a Jeep, its supposed to do that!" The truth of the situation
is that vibrations can rob you of some very important things.
The first thing
you lose is the comfort and smooth operation of your expensive Jeep.
The second thing you loose is reliability on and off-road. The constant
vibration and resonance of the driveline shakes bolts and u-joints
The last thing
is horsepower. Yes, horsepower! What do you think actually powers
the vibration? The power from the engine makes it through the transmission
to the transfer case and then to the rear drive shaft. If all of
that power makes it to the rear axle, you feel it as forward motion
of the Jeep. If there is something binding in the driveline, that
energy is being transferred into a vibration and not forward momentum.
The power loss may be minor in most cases but think about how many
horsepower it takes to shake your whole Jeep with a vibration. I
just installed a K&N air filter in hopes to gain 5-10 hp. What
if I am losing the same amount in my driveline due to a poor drive
we opened the can we have to deal with it right? Right! There are
several ways to deal with this vibration problem.
can typically remove those transfer case drop kit spacers
once you do a SYE kit and tuck your t-case back up where it
JB Conversions SYE kit and the Tom Wood drive shaft combine
to give you everything you need for a better driveline angle,
including a new output shaft housing for the transfer case.
stock (left) output shaft housing will be replaced with a
brand new housing (right) from JB Conversions, which will
help lengthen the driveline.
fat, beefy, stout. These are all perfect adjectives you can
use to describe the JB Conversions output shaft (top). Looking
at the realatively dinky stock shaft (bottom), you can see
why Option B+ is not the best way to go.
manufacturers are well aware of the driveline issues in Jeeps. Most
of the kits you can buy will include some sort of transfer case
drop kit. What this does is place spacers between your frame and
transfer case skid plate. This accomplishes two things. First, it
lowers the transfer case closer to the rear axle height in order
to decrease the angle of the rear drive shaft. Secondly, it tilts
the case slightly to alleviate the strain on the upper u-joint.
Drop kits also
have several negative effects, though. You lose some of your precious
ground clearance you were trying to gain by installing the lift.
Your shift levers are now shorter in the cab of the Jeep and may
even require floor trimming in some models to make them work right
in second, fourth, and reverse. This is more common in YJ's than
TJ's. It also causes an extra bind on the motor mounts since the
engine is now tilted rearward.
model 231 transfer case found in the Jeep Wrangler since 1987 is
too long and uses a slip yoke design at the back of it. The drive
shaft slips into the back of the case making the rear seal of the
transfer case. If, for some reason, you have to remove the rear
drive shaft you will lose all the fluid inside the case. This is
because there is no longer any type of oil seal. This means that
if you break that rear drive shaft or u-joint on the trail you CAN'T
limp it home in front wheel drive. Editor's note: We have seen
people plug the hole with everything from rags, to duct-taped in
plastic soda bottles.
A slip yoke
eliminator kit (SYE) uses a C/V (constant velocity) joint, which
bolts on to the back of the transfer case. The kits eliminate the
slip yoke (thus the name) and use an oil seal to keep the fluids
inside. By eliminating the slip yoke design on the back of the transfer
case, you benefit in several ways. First, you can shorten the overall
length of the transfer case output shaft by 4-6 inches. This translates
to 4-6 inches that you can use for a longer drive shaft. This alone
makes for a better drive line angle without lowering the transfer
case. It also gives you the ability to remove the rear drive shaft
should you break it.This
means that you CAN limp it back home in front wheel drive.
It also means
that your shift levers etc. stay where they were designed to be,
because in most cases, you can get rid of that transfer case drop
kit and tuck the case back up where it belongs. This actually makes
the Jeep run and drive like it was designed to do. The SYE kits
and drive shafts integrate into a Jeep seamlessly. You will have
to keep in mind, though, that the rear pinion angle needs to be
adjusted, no matter which method you use.
are several SYE kits out there on the market. Some of the options
include cutting, drilling and tapping your current output shaft
to shorten the overall length. While this is the cheapest option
and can certainly be effective, it is in my opinion a cut and paste
approach that does not seem to offer much consistency from the installer's
stand point. What if I cut wrong, drill crooked or tap it wrong?
The best approach
is to buy a kit that includes a whole new shaft to put inside the
transfer case. The kit from JB Conversions is exactly that. It is
a heavy-duty shaft made to the exact transfer case manufacturer's
specifications. This means that not only do I get to put NEW parts
in the Jeep, but I have also now increased the strength of my transfer
The JB Conversions
shaft has an 18% larger shaft diameter than the stock NP231 shaft.
The shaft also has 32 splines compared to the original 27 splines.
That gives the shaft a 54% increase in torque capacity. The JB conversions
kit comes with everything you need for the transfer case, including
a NEW rear tail housing.
The JB Conversions'
set up places the output at the shortest possible point without
sacrificing the manufacturer's design specifications. That is why
it comes with the new tail housing. This makes it the strongest
and most reliable SYE kit on the market. I don't want to have any
worries about the integrity of my transfer case on or off-road.
Doing it right the first time means that I won't have to do it again.
And as long as we are upgrading to a heavy duty transfer case, we
may as well upgrade to one of Tom Wood's heavy-duty rear drive shafts.
Conversions vs. Stock
is the stock setup. Notice how long the output shaft is and
the corresponding housing.
is the new, JB Conversions output setup. It's tucked in further
and the shaft is a lot shorter.
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