Joints: A universal joint is defined as a "shaft coupling
capable of transmitting rotation from one shaft to another not collinear
with it." In other words, it is a mechanical device that transmits
torque / rotary motion between two shafts that are not in a straight
There are 2 types, the:
1)Cardan style universal
joint; and the
2) Constant velocity
We shall explore them
Style Universal Joint
common type we encounter is the cardan style universal joint, developed
by Spicer, and pictured
to the left. This is the familiar "cross and caps" style
universal joint, often just referred to as a "U-joint".
Remember though, that technically it is a cardan style universal
The way the cardan style
universal joint works is as follows (and this is very important
First - why do we need
to use a universal joint in the first place? The answer is easy,
and can be surmised from the above definition.
It is because we need
to transmit torque from the transfer case to the axle pinion, and
of course, the transfer case and pinion are not collinear - they
are not in a straight line. The t-case is above the pinion (obviously)!
Therefore there is an angle between them. In order to transmit torque
or rotation between 2 shafts that are at an angle, we must use a
universal joint. In the automotive driveshaft world, 99% of the
time that means we use a cardan (cross) style universal joint.
||Because of the way the
cardan style universal joint operates when the 2 shafts it joins lie
at an angle (see pic to left - the joint cross or body rotates about
it's center, while at the same time the caps rotate around their trunnions),
the result is that the joint follows an elliptical, rather than a
To visualize how this
occurs, look down the length of a rear driveshaft at the U-joint
in the transfer case yoke. If the pinion end of the driveshaft were
unbolted from the differential and lowered to the floor, it would
create a severe angle in the forward U-joint. If the shaft were
then turned by hand, you’d then be able to see that the two
bearing caps on the U-joint center cross attached to the driveshaft
rotate in one plane while the two attached to the transfer case
yoke rotate in a different plane. All the while the center cross
is swiveling back and forth with each revolution.
The best way to illustrate
this is to hold 2 shafts coupled by a U-joint in your hand and rotate
them- you will quickly see exactly what I mean. The crude drawing
to the left may also serve to illustrate what is happening. I have
drawn in blue a representation of a second yoke on the other side
of the joint from the actual yoke pictured. Now, what happens is,
the real yoke and the blue yoke, connected by the U-joint, both
rotate around in the direction indicated by the long double-headed
arrows. To accommodate the angle between the 2 yokes, the bearing
caps each rotate around on their respective trunnions, as indicated
by the short double-headed arrow. The result of the combination
of these two motions is the U-joint swiveling back and forth each
revolution, in a sort of see-saw back-and-forth motion, as indicated
by the "V" shaped double-headed arrow. Ultimately, this
leads to the elliptical path of the bearing caps, when viewed longitudinally
down the shafts.
||If you drew what’s
happening on paper (and of course I have done that for you :-), the
two bearing caps in the transfer case yoke would appear to be traveling
in an elliptical (oval) shaped path as viewed down the length of the
driveshaft (blue ellipse). Or, from the other point of view, the two
bearing caps on the driveshaft would appear to be traveling an elliptical
path if viewed from the transfer case (red ellipse). It is this difference
in geometry that causes the driven shaft to change speed with respect
to the driving shaft.
So, we have two different
shafts, connected by a universal joint operating at an angle. Because
of this, the ends of the u-joint in each of the yokes in the 2 different
shafts (the t-case output yoke, and the yoke at the transfer case
end of the driveshaft) both travel in elliptical paths, but the
paths are 90° offset (out of phase) from one-another. In the
pic to the left, the blue ellipse represents the path of the input
shaft (t-case yoke) and the red ellipse represents the path of the
output shaft (driveshaft yoke). Because the 2 shafts are connected
to opposite bearing caps, their elliptical paths are offset 90°,
as can be seen in the pic.
Now, the problem is,
the t-case output is driven from the crankshaft by gears and/or
chain drive at a fixed rate (angular velocity) - let's say 1000
rpm for example. Of course, because the driveshaft is mechanically
connected to the t-case output, it also must be rotating at 1000
rpm. In the pic, the green arrows show where the two elliptical
paths cross, the points of intersection. At these points, the 2
shafts must be in the same place at the same time (otherwise the
assembly would come apart.) In order for this to happen, you can
see that at times the driveshaft's elliptical path (red ellipse)
is longer than the t-case yokes (blue ellipse) and vice versa. So,
in order for the assembly to remain together and driven at a fixed
rpm, the driveshaft must have to speed up and slow down at different
points along it's path in order to match the t-case yoke that is
being driven at 1000 rpm. The black arrows show where this happens.
In this case, the driveshaft will speed up and slow down a total
of 4 times per revolution. That is, it speeds up, slows down, speed
up, slows down, then repeats. This is the reason why we say a cardan
style universal joint transmits rotation/torque with a "variation
in angular velocity between the input and output shafts".
This speeding up and
slowing down can cause vibration of the driveshaft and significant
wear on the universal joints if not properly accounted for in the
driveshafts design. This "accounting for" is what we call
driveline geometry and will be discussed in great detail in part
For now, remember that
a u-joint must be used because there's an angle between the t-case
and pinion (and often a very big angle in the case of lifted 4x4s
- which is why this whole driveshaft business is so important to
us in the first place). When a u-joint is used, and operates at
an angle, the bearing caps on the input and output shafts will describe
elliptical paths offset by 90° from one-another because of the
difference in geometry between the two opposing bearing caps in
the U-joint. Since they travel in elliptical paths, and yet must
remain fixed together driven at a constant rpm the driveshaft must
therefore speed up and slow down twice each per revolution. This
difference in angular velocity between the 2 shafts causes noise,
vibration, and u-joint wear, and must be accounted for in proper
The speed changes are
not great when the angle is less than a few degrees, but as the
operating angle of the joint increases so do the cyclic vibrations
of the driven shaft as well as the back and forth motion in the
You can read about the
different types of Spicer cardan-style universal joints at spicerdriveshaft.com
(CV) Universal Joint:
In marked contrast
to the cardan style universal joint, a true constant-velocity (CV)
universal joint is one that transmits torque/rotation with an angular
velocity ratio of unity between input and output shafts. In other
words, even at an angle, the input and output shafts travel at the
same (Constant) speed (Velocity) hence the name - Constant Velocity.
CV universal joints are not common in 4x4 driveshafts, but are very
common in front wheel drive car half-shafts (axles). The pic to
the left shows a very common style of CV joint, the Rzeppa joint,
invented in 1920 by a Dana engineer named Alfred H. Rzeppa
Their common use in fwd
cars is because the joints in the half shafts must accommodate being
driven at high speeds for long times as well as changing compound
angles due to the front wheels being steered and the front wheels
cycling up and down with the suspension. As such, the inner and
outer joints in a fwd car half shaft often operate at different
angles. Whenever the wheels are turned the outer joint runs at a
much higher angle than the inner joint. This upsets the offsetting
relationship between inner and outer joint angles that’s a
necessary requirement for ordinary U-joints. What’s more,
the front wheels are required to steer at angles of up to 45 degrees—which
puts too much strain on a U-joint.
A CV joint, by comparison,
always splits the operating angle in half so the driven shaft turns
at the exact same speed as the input shaft. So no matter what the
joint angle, there are no changes in speed -- thus the name "constant
A driveshaft is a device
that connects the transfer case to the axles, transmitting torque
from the engine to the driving wheels. It is also called a propeller
shaft or prop-shaft for short (mostly by Brits and Aussies). Virtually
all driveshafts (certainly all that I know of) fit into one of two
often misunderstood broad categories. They are:
universal joint driveshafts, subdivided into:
universal joint shaft; or
universal joint shaft
|| Pictured at left - double-cardan-style
universal joint shaft on top (my new High
Angle Driveline shaft) and a single-cardan-style universal joint
shaft (the junk I took out!)
that, as you would expect, the double-cardan shaft has one end (the
transfer case end) that has a joint that contains, two cardan-style
u-joints - forming the "double-cardan" portion. More on
Velocity (CV) joint style driveshafts.
This is an important
distinction, if only academically. You see, true CV joint driveshaft
are rare in 4x4 driveshafts (some earlier Jeeps came with GKN
CV style front driveshafts that were tiny and weak)
CV joints are, however,
extremely common in FWD car half shafts (half axle shafts). Pictured
at left are some GKN half-shaft CV joints. Virtually all modern
cars have them. Virtually all are made by GKN's automotive driveshaft
There are many different
types of CV joint, including Fixed Ball, Single Roller Tripod Plunging
Joint, Ball Plunging Joint, etc. You can read about them at http://www.add.gknplc.com/products.htm
None have anything to do with our needs and heavy-duty 4x4 driveshafts.
WHAT???? You cry. But
everyone's always talking about CV driveshafts - heck the title
of your own article is "1 Ton CV driveshaft" you hypocrite!
You're right - you see,
the very common double-cardan-style universal joint shaft (pictured
above, upper shaft in pic), is properly called a "near constant
velocity, double-cardan-style universal joint shaft." (incidentally,
this "velocity" we keep referring to is the angular velocity
of the joint in the shaft). Now, what has happened is that because
"near constant velocity, double-cardan-style universal joint
shaft" is such a huge mouthful, it has become common practice
to drop the "near" , "double-cardan-style",
and "universal joint" and what we are left with is common
convention leading to a double-cardan-style universal joint shaft
simply being referred to as a CV shaft.
There - now you know
the truth, and you can amaze your friends (or getting soundly beaten
by them for being a nerdy smart-ass) at the next trail-side campfire!
So, we know that true
CV joint driveshafts are of no interest to us, so forget them now.
That leaves us with either single or double cardan style driveshafts.
The latter, I shall bow to convention, an henceforth refer to them
as CV driveshafts, simply because everyone does.
Now, whether a 4x4s driveshaft
is single cardan (also called "regular' or "single-joint"
or simply "U-joint) or CV, there is one more distinction to
All driveshaft's must
have some way of changing length, allowing the driveshaft to shorten
or lengthen as required, to accommodate suspension movement. This
is because suspension movement will cause the distance between the
output of the transfer case and the yoke on the axles pinion to
change somewhat. How much the distance changes, and therefore how
much "accommodation" you need in your driveshaft will
depend on a lot of different factors, including suspension geometry,
amount of wheel travel, whether the diff on the axle is centered
or offset, etc. For example, a 4 link coil sprung rear axle with
center limiting strap will require significantly less length change
accommodation than a soft leaf-spring-over-axle front axle with
shackle reversal, offset diff, and no limit straps. The former may
require only an inch or 2, the latter many inches. The only way
to know for sure is to flex the suspension and measure.
The 2 common methods
of accommodating this length change, or slip, are:
1 - Slip-yoke shaft.
This style is a very common late model rear driveshaft factory style.
It comes stock in a great number of 4x4s, including Jeeps, Chevy's,
and many others. The slip-yoke is an internally splined tube that
slips into the rear output of the transfer case. As the name implies,
the slip yoke slips in and out of the transfer case output housing,
to accommodate driveshaft length change. generally, this type is
not favoured by the hardcore crowd as it's drawbacks generally include:
- Small u-joint size
- Small tubing (stock)
- Limited travel in
the slip yoke
- The fact that the
transfer case output is sealed by the slip yoke, meaning that
if you break a u-joint or the shaft, and have to remove the slip
yoke, you have to have some sort of method for plugging the transfer
case output hole, otherwise the t-case will lose all its fluid.
That said, High
Angle Driveline can build you a 1350 1 Ton CV slip-yoke driveshaft.
The pic to the left is just such a shaft.
2 - Slip-member shaft. This style is common on trucks and
4x4's, especially older trucks, and is the most desirable type.
They use a splined section incorporated in the shaft itself, called
the slip-member, which allows the shaft to change length.
The pic to the
left is my new shaft installed, which is a slip-member style shaft.
The slip-member is easily visible between the red arrows.
||Now that we know all about
the different types of shafts, this picture illustrates the names
of the various parts of the drive shaft. Where there is more than
one common name, the alternate names are shown in brackets.
U-joint Series / Sizes
So we know all about
the different types, and all the parts, the last thing we need to
know before we can fully and accurately describe and talk about
driveshafts is the relative size (and therefore strength), normally
determined by and referenced to, the size (series) of the U-joints
used in the driveshaft.
A U-joint "series"
is a number that describes a group of cardan style universal joints
by common dimensional grouping. A series number is not an actual
specific part number.
The common U-joint series
used in light truck and 4x4 driveshaft construction, with dimensions
listed corresponding to the diagram are:
width (W) (inches)
diameter (D) (inches)
Duration rating (lb-ft)
- Bearing Cup Assembly
— Consists of a bearing cup with needle rollers generally
held in place by a seal guard and bearing seal. Sometimes the
assembly includes a thrust washer.
- Bearing Cup —
A cup-shaped member used as the bearing bore of a bearing cup
assembly and for positioning a thrust end of a cross trunnion.
- Bearing Seal —
A flexible member of a bearing cup assembly which prevents the
escape of lubricant from or entry of foreign matter into a bearing.
- Boot — A flexible
member which prevents the escape of lubricant from or entry of
foreign matter into the slip member assembly.
- Boot Clamp —
A thin adjustable band used to hold the boot in position on the
slip member assembly.
- Boot Seal —
- Companion Flange
— A fixed flange member that attaches a steering shaft (intermediate
shaft) to a steering gear box or steering column shaft.
- Cross — See
- Cross Hole —
A through hole in each lug ear of a yoke used to locate a bearing
- Ear— One of
two projecting parts of a yoke symmetrically located with respect
to the yoke’s rotational axis.
- End Fitting —
An end yoke or companion flange that attaches a driveshaft to
a transfer case or axle (pinion).
- End Yoke — A
yoke that attaches a driveshaft to a transfer case or axle (pinion).
- Flange Yoke —
A full-round style yoke which attaches a driveshaft to a transfer
case or axle (pinion).
- Glidecote® —
The blue, nylon, wear-resistant coating on Spicer yoke shafts.
- Grease Zerk (Nipple)
Fitting— The fitting on the shoulder or center of a journal
cross that allows for lubrication.
- Inboard Yokes —
Yokes that make up the ends of a driveshaft.
- Intermediate Shaft
— See Steering Shaft.
- Journal Cross —
The core component of a universal joint which is an intermediate
drive member with four equally spaced trunnions in the same plane.
- Lug Ear — See
- Needle Roller Bearings
— See Needle Rollers.
- Needle Rollers —
One of the rolling elements of a bearing cup assembly.
- Outboard Yokes —
Yokes that are not a part of a driveshaft (i.e. yokes that are
part of a transfer case output or axle (pinion) input.
- Phasing — The
relative rotational position of each yoke on a driveshaft.
- Pinch Bolt —
Bolt used to compress slotted end fittings for retention.
- Purge— The
act of flushing old grease and contaminants from universal joint
kits with fresh grease.
- Slip Member Assembly
— Combination of slip spline, slip yoke and boot assembly.
- Slip Spline—
A patented tubular-type, machined element consisting of internal
splines in a driveshaft assembly.
- Slip Yoke —
A slip member yoke with a female machined spline used for axial
- Slip Yoke Plug —
See Welch Plug.
- Snap Ring —
A removable member used as a shoulder to retain and position a
bearing cup assembly in a yoke cross hole.
- Snap Ring Groove—
A groove used to locate a snap ring.
- Spline — A
machined element consisting of integral keys (splined teeth) or
keyways (spaces) equally spaced around a circle or portion thereof.
Any of the four projecting journals of a cross.
- Universal Joint —
A mechanical device which can transmit torque and/or rotary motion
from one shaft to another at fixed or varying angles of intersection
of the shaft axes. Consisting usually of a journal cross, grease
zerk (nipple) fitting and four bearing cup assemblies.
- Universal Joint Kit
— See Universal Joint.
- U-Joint — See
- Welch Plug—
A plug in the slip yoke face that seals off one end of the spline
opening. Also known as a slip yoke plug.
- Yoke Lug Ear Cross
Hole — See Cross Hole.
- Yoke Shaft —
A slip member yoke with a male machined spline used for axial
So now that we know all
the terms and definitions regarding Driveshafts, what else do we
need to know to get the best, world class, bulletproof driveshaft
under our truck?
Well - the answer is
....depends. It depends on what kind of person you are. If you just
want the job done, so you can get behind the wheel, the answer is
NOTHING. You simply call up Jess
at High Angle Driveline
@ (530) 877-2875 and have a nice chat with him about your needs.
He will help you with whatever you need, discuss your options with
you, and be pleased to talk to you about driveshaft tech, and his
customer service is second to none.
However - if you're a
tech-geek like me - you want to know more.
Before we get to the
actual install of my 1 ton 1350 CV driveshaft, I'll cover the following
- Driveshaft Geometry
- How to choose
a driveshaft for your rig
- Driveshaft Maintenance
- safety, inspection,
- removal, replacement,
- U-joint Tech
- Causes and analysis
of driveshaft failure
- Spicer stock driveshaft
- Spicer driveshaft
- Spicer part number
- Driveshaft / U-joint
- Spicer driveshaft
- Spicer driveshaft
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