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Rear Suspension
As with the front suspension, the rear suspension is very important when you’re building a
performance Restomod. These cars are supposed to be driven, and driven hard. This chapter will
go over different factory and custom rear suspension systems for your Restomods. It will also
explain how to get the best all-around performance out of your rear suspension.

There are two typical types of rear axles: live axle and independent rear suspension (IRS). The live
axle consists of a rigid housing that contains the axle shafts and differential, with wheels mounted
solidly on both ends—this is the rear end that most of us are used to seeing under cars. Any travel
or motion from the left tire directly affects the right tire, since they are both attached to the axle. A
live axle is attached to the car’s frame using links, bars, or leaf springs. There are many different
link configurations. When it comes to locating the live axle, the concept is basic. The axle needs to
have limited fore and aft movement. It also needs to have limited travel from side to side. All this is
needed, while still allowing the axle to move up and down. From those basic principals, live-axle
rear suspension gets complex.
Pinion Angle
The pinion angle is simply the angle between the rear end’s pinion shaft and a true horizontal line.
The transmission angle is the angle between the transmission’s tail shaft and a true horizontal line.
Together, these angles form the driveline’s phase angle. Pinion angles can make the difference
between a smooth ride, or a noisy and shaking ride down the freeway. Correct pinion angles are
also very important to the life of your U-joints. Over time, the angles can change and become
incorrect due to loose factory tolerances, body and frame alignment, and changes in spring rates
due to wear. You should check and correct pinion angles any time you change the ride height or
modify the rear suspension. Even changing leaf springs can change the pinion angle.

Hot rod shops and seasoned backyard mechanics commonly overlook pinion angles. When I was
doing research on this subject, I found out why it seems like there is very little information about it,
and the little bit of information available seems to be contradictory. After a lot of research, I decided
to enlist the help of Kyle Tucker (an ex-GM suspension engineer). It turns out that pinion angles are
not a Jedi secret, though they differ for each application. Family trucks, production sports cars, and
Restomods are not built for the same type of driving. I am going to cover pinion angle settings for
Restomods built for street and road course racing, since the book isn’t strictly covering drag racing,
Baja racing, swamp buggy racing, or grandma cars.

Maybe you’re building a full-tilt tube chassis to slide under a Fairlane shell. The best chassis
designers determine the ride height first by positioning the rear axle, the correct size of tires, and
the wheels under the body. Once they do that, they set the transmission height and angle, and
then build the rest of the car around that. If your car is finished or you are in the middle of a build-
up, don’t worry. These angles can be adjusted later, but it would be better if the car were designed
around the correct angles to begin with.
Examples of two different angle gauges
Checking Pinion Angle
Here are two types of angle
gauges. The analog gauge on
the left can be purchased from
most hardware stores. The
digital SmartTool is more
expensive. Both show that the
rack is very close to zero
degrees, which means the
suspension is loaded correctly.
Checking pinion angle correctly is important. Start by getting an angle gauge. A few types are
available. The most common is an analog magnetic-base protractor gauge (pictured in photos
checking angles). These are available for about the cost of a meal at your local restaurant. Other
types, such as digital angle gauges, are far more expensive. They basically do the same job, but
they’re much more precise.

Next, find a place to check your angles. Using a four-post rack or a pit is the most accurate way.
The car should be on a level surface and at ride height. To get the ride height correct, you should
fill the fuel tank. Fuel can add a lot of weight and change the ride height of the car. If the car is not
level on the rack and resting on all four tires, your readings will not be accurate.
If you don’t have access to a four-post rack or pit, you can use jack stands and/or ramps to
simulate the fully loaded ride height. Do this on a hard, flat surface and make sure the car is level.
You should place jack stands safely under the rear axle tubes. Do not use a floor-jack to support
the front of the car. This is very unsafe. The front of the car needs to be lifted exactly as much as
the rear of the car. If you are using jack stands under the front of the car, placement is very
important. If you place the stands under the frame in front of the centerline of the spindle, you will
be placing more of the vehicle’s weight on the rear suspension. If you place the jack stands under
the frame behind the spindle centerline, you will be moving some of the load off the rear
suspension. This factor will cause incorrect measurements.
Compressing the rear suspension to measure driveline angles
This is another way to lift
the car up for measuring
the pinion angle. Make
sure to do this on a flat,
safe surface. Place jack
stands safely under the
rear axle to compress the
suspension as if the car
were on the ground.
The most precise way to set your car up for measuring pinion angle, without a four-post rack, is to
use two sturdy car ramps and two sturdy jack stands. Start by driving the front of the car up on the
ramps. Safely place jack stands under the left and right rear axle housing tubes. At this point, the
front and rear of the car have to be raised evenly. If the ramps raise the front tires up 9.75 inches
off the ground, the rear jack stands should support the rear axle so the rear tires are 9.75 inches
off the ground. This will ensure you have lifted the front and the back of the car evenly for
accurately measuring pinion angles. Don’t forget: safety comes first.
Measuring the transmissions angle to calculate the driveline angles
The transmission angle can be
measured off the yoke or off
the tail-shaft seal. Here, a
straight bar was pressed up
against the seal with the
magnetic-base angle gauge
attached to read the
transmission tail-shaft angle.
The angle on the transmission is typically measured off the back of the transmission on the
driveshaft yoke’s seal surface. It can also be measured off the engine block, since the oil pan’s
gasket sealing surface is parallel to the crankshaft (just take into account that there is a 90-degree
angle difference from the transmission angle). The pinion angle on the rear end is taken from the
face of the pinion yoke. Finding the flat surface on the transmission and the pinion yoke is easy,
but there may not be space to place your gauge. If you have a metal straight edge, you can rest it
against the flat surface and attach your magnetic gauge to the straight edge.
For a car that is set up for handling around corners, the optimum pinion angle is different than if
you were setting your car up for serious drag racing. Incorrect pinion angles can cause chassis
vibration and premature U-joint wear and failure. Without the correct angles, the needle bearings in
the U-joint caps do not rotate (as shown in the U-joint section). Those needle bearings need to
rotate in order for the U-joint to operate reliably and smoothly.
Correct driveline angles for vehicles with leaf springs
This picture shows phasing angles that should be used for most leaf-spring Restomods. Notice
the pinion and transmission angles are both down.
Driveline angles as most production cars come from the factory
This picture shows how phasing angles are set up on most production passenger cars. Notice the
differential pinion angle is as many degrees up as the transmission angle is down. The angles are
parallel. Without load on the suspension, the angles total 6 degrees. These angles should add up
to a maximum of 7 degrees.
Driveline angles change with heavy acceleration
This picture illustrates the problems with running parallel phasing angles. The differential is shown
with a torsional load from acceleration. The pinion tries to push upward, causing the springs to wrap
up. At this point, the maximum tolerable angle of 7 degrees has been exceeded. This is bad for
U-joints.
Correct driveline angles for a vehicle with coil spring rear suspension
In this picture, you can see the pinion angle is set fewer degrees down than the leaf-spring set-up.
This is how short-track coil-spring suspensions should be set up. Unlike leaf-spring suspensions,
the trailing arms used in a coil-spring suspension typically minimize upward movement of the pinion.
Optimum Pinion Angle
Now that you know how to measure pinion angle, it’s time to find the optimum pinion angle. There
are many different schools of thought in this area of suspension tuning. I am going to go over
pinion and transmission angles. Both angles are equally important when it comes to optimum
suspension tuning. When referring to both angles combined and their relation to each other, they
are referred to as phasing angles.

Pinion angle depends on your application. Production passenger cars and basic street cars
operate fine with parallel pinion and transmission shaft angles. Many shops still use this old-school
design for building cars, and it’s fine for street use. However, if you are going to build a car that will
be pushed to its limits on a road course, then forget that school of thought. During acceleration,
torque causes the pinion to tilt upward. If you set your pinion angle a few degrees upward, the
pinion will want to travel even further upward during acceleration. This is explained in more detail in
the leaf spring section. The most common transmission shaft angle is 2 to 3 degrees down. Leaf-
spring suspensions allow the pinion angle to rotate upward when the springs wrap up under
acceleration. Angling the pinion downward compensates for this upward travel. Serious short-
course race cars run a pinion angle of as much as 4.5 degrees down. A downward pinion angle of
2.5 to 3 degrees is a good place to start for Restomod (high-performance street and road course)
applications.

The combined pinion and transmission angle should not exceed more than 7 degrees. A combined
pinion angle of 3 degrees and transmission angle at 2.5 degrees add up to 5.5 degrees, which
does not exceed the maximum. If you run parallel phasing angles like some old-school street
rodders have been using, you can easily run into problems. For example, think of the transmission
angle set at 3 degrees down and the pinion angle set up 3 degrees to run parallel with the
transmission. When the leaf spring wraps up, the pinion angle can rotate upward 2 or more
degrees. If you add the transmission angle at 3 degrees to the pinion angle of 3 degrees, it would
add up to 6 degrees combined. During wrap-up, the 6 degrees can become 8 or more degrees,
which exceeds the maximum allowable range totaling 7 degrees. This will dramatically shorten the
life of your U-joints.

Restomods equipped with coil-spring rear suspensions can run with less downward pinion angle.
The trailing arms on a coil-spring suspension typically limit the amount of pinion lift (where the front
of the differential tilts upward), so pinion angle can be set at 1.5 degrees down.
Pinion Angle Adjustment For Leaf-Spring Suspensions
On leaf-spring suspensions, there are a couple of ways to adjust the pinion angle. The more
common way is to install shim-style wedges, which are available in different degrees from several
manufacturers. The other method is to install a pair of adjustable leaf-spring pads. These are great
for project cars that will not be sitting at fully loaded ride height for quite some time. They can be
installed early in the process of a project, then adjusted and welded later when you’re close to
finishing the car. They’re a nice alternative to welding a stationary spring perch to the differential
housing early on in a project, and having to use shims to adjust the pinion angle later.

There is an alternative to welding the adjustable perch, too. Once they’re installed and the pinion
angle is adjusted, carefully drill a hole through each perch and axle tube. Then thread the hole in
the axle tube to accept a bolt. Disassemble the rear end to clean all metal debris from inside the
axle housing, and then reassemble the rear end. This is not the easy or preferred method, but it is
an alternative for people without welders.
Previous | Next


This has been a sample page from

How to Build Ford Restomod Street Macnines How to Build Ford Restomod Street Machines
by Tony E. Huntimer
This book Should be called
"How to Build High Performance Fords!"
This is one of the best books we've seen about building high
performance Fords. It contains sections on upgrading brakes
and suspension, improving chassis stiffness, engine choices
and engine swaps, drivetrain choices including
production and
after market transmissions, electrical
systems and even body
modifications. It even has sections
to help you find the right
project car for as little money as possible and where to find the
parts you need to complete your project. This is one of the
best, if not the best book out there about building and

modifying Fords for improved performance. Best of all, this
book is not just about the Ford Mustang as many other Ford
books are. Read the sample pages to learn more!
Click below to view samples
pages from each chapter
Chap. 1 - Shocks & Sway Bars
Chap. 2 - Front Suspension
Chap. 3 - Rear Suspension
Chap. 4 - Frames & Chassis
Chap. 5 - Engine Swaps
Chap. 6 - Transmissions
Chap. 7 - Body & Glass Mods.
Chap. 8 - Finding Parts
8-1/2 x 11"
Softbound.
144 pages
Approximately 300 b/w photos
Item: SA101P
Price: $23.95
Click here to buy now!


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