Understanding
Bump-Steer,
its
effects on drive-ability, and ways to
correct the
problems and or symptoms
Why is Bump-Steer so
confusing?
Bump-Steer
can be a very complicated and confusing issue. Grasping
suspension geometry can be difficult, in and of itself, but with
Bump-Steer there are two factors that increase the complication and
cloud the real issues. The
first factor is that, when it comes to poor handling, Bump-Steer is the
"chicken" of the automotive world. In the same way that
everyone
says "that tastes like chicken", automotive enthusiasts say of a poor
handling car, "this car suffers from Bump-Steer." I find it
fascinating that simply by taking a test drive, many backyard
mechanics, car enthusiasts, and even some automotive professionals can
diagnose Bump-Steer as the problem with 100% confidence, especially
when they have a limited understanding of what Bump-Steer really is and
what causes it.
It is much like a young doctor diagnosing a
serious and complicated illness in a patient simply by asking them a
few questions instead of doing any real tests. Please
don’t
misunderstand, I am in no way saying that if a car is handling poorly
that Bump-Steer is not a possible cause. What I am saying is
that
Bump-Steer may in deed be the issue, however, it is just as likely that
the problem has another cause or a combination of causes.
Just as
a doctor must know the actual source of the problem to successfully
treat his/her patient, we, as car enthusiasts, must accurately diagnose
the true issue in our suspension and handling problems to effectively
correct them. Also, we must remember that, similar to the
medical
profession, sometimes more relief is found in dealing with the symptom
or "effect" of the problem rather than the real issue.T his brings me to
the second factor that
makes Bump-Steer such a confusing issue, and that is; the amount of
measurable Bump-Steer is not always in a direct ratio with the amount
of Bump-Steer that is actually felt when driving the
vehicle. I refer to this phenomenon as the
“Bump-Steer
Effect".
What I mean to say is, if you look at a
car’s
suspension, there are physical quantifiable measurements that can be
taken to identify the actual amount of “Measurable
Bump-Steer” that is
present. However, these numeric measurements may vary from
the
actual handling and drivability of the car. A car with large
amounts of measurable Bump-Steer may suffer from little to no actual
"effects" of Bump-Steer, or on the flip side of that coin, a car with a
small amount of or even no Measurable Bump-Steer may have horrific
handling and drivability due to extreme Bump-Steer Effect.
Don't
get me wrong, as the "measurable" amount of Bump-Steer increases, in
theory, so will the "effect", but, due to all the other suspension
parts, their role in handling, and the variables they bring to the
equation, the Bump-Steer effect can range from non-existent to
extreme. To make matters worse, even though Measurable
Bump-Steer
and the Bump-Steer Effect are two separate, yet related things, they
are almost always referred to as one in the same. This adds
tremendous confusion to the issue and, in an effort to alleviate this
confusion, from here on out it is paramount that we realize that
Measurable Bump-Steer and the Bump-Steer Effect are separate issues
and, henceforth, WILL be referred to as such.
Measurable
Bump-Steer (MBS):
Whether we like it
or not, almost all
stock early automotive suspension systems, and even many modern
suspension systems, have some degree of MBS. The measurement
of
Bump-Steer is the difference of suspension and steering components
moving in different arcs as the suspension compresses and
decompresses. Here is a simplified definition of MBS:
Measurable Bump-Steer is a situation where the suspension components
travel to a point were the distance moved is not equally compensated
for by the movement of the steering components and, thus, one or both
wheels are pulled into an unintended turning position.
Bump-Steer is
measured by comparing the
arc and the positioning of the outer tie rod and the arc of the
spindle. The spindle arc is created by a combination of
movement
of the lower control arm and the A-arm. If the
spindle arc
and the tie-rod arc are the same, then zero MBS exists. The
picture below illustrates this; the red arc to the left is the arc of
the spindle, and the inner red arc is the travel of the tie
rods.
If the two red arcs match in radius then no MBS exists, but if the arcs
differ then MBS is present. Also, in the picture, the green
arcs
illustrate the A-arm and LCA movement.
When a car is
aligned, all of the
adjustments are made with the car in a nonmoving, resting
position. That means that regardless of the amount of MBS
present, when the car is in a resting position, the wheels are pointed
in the direction they were aligned to point in, and when a car is
sitting motionless, the suspension should be at, or near, the middle of
its travel arc. In suspension systems where MBS exists, the more
extreme the suspension travel then the more severe the Bump-Steer
measurement as the suspension components move away from the position
they were in when they were aligned.
With all that
said, tie rod length is
the main factor in MBS. If you shorten the tie-rod assembly,
then
its arc decreases and, in reverse, if you lengthen the tie-rod
assembly, then its arc increases. That means that the simple
act
of adjusting the toe on your car will either add or reduce the amount
of MBS. When the arc of the tie rod is smaller than the arc
of
the spindle, then the car’s suspension system is referred to
as having
positive MBS because the distance between the two arcs increases as the
suspension moves away from its resting position. In reverse
of
that, a tie-rod arc greater than the spindle arc will result in
negative MBS.
Keep
in mind that MBS is a geometric defined phenomenon that is present or
it isn't! Almost all cars have some amount of MBS and a
Bump-Steer kit or modifying suspension and steering components, such as
the spindle steering arm or the inner tie rod location, are the only
ways to truly eliminate MBS. Also, keep in mind that to accomplish any
of the above-mentioned MBS removal techniques, special measurements are
required to insure that MBS has been removed and fine-tuning will be
required every time the car is aligned to maintain zero MBS.
Also, there are several performance “upgrades” that
increase MBS, such
as some rack and pinion units, as well as Granada disc brakes on an
early (64.5-66) Mustang. Keep in mind that such upgrades may
require other performance components that will help reduce the
Bump-Steer Effect.
The Bump-Steer Effect
(BSE):
We
have
established that adjusting tie
rod length when doing a simple alignment will change the geometry and
affect MBS. As a whole, this is not a problem because,
depending
on suspension components, variable amounts of MBS can be absorbed by
the suspension. Look at it this way: If your car is
aligned
properly, then both tires should be set with a small, yet equal, amount
of toe in. If, due to MBS, one tire is pulled further toe in
or
toe out, the other tire is still pointing in the correct direction and
will help keep the car on the road.
Even with
a
Mustang with completely
stock suspension and steering components, there will be some BSE, and
there are many things that can be done to lessen or remove the
BSE: Roller Spring Perches, Adjustable Strut Rods, 1" Shelby
Drop, and, most importantly, a Performance Alignment. As
these
modifications reduce the BSE, there are also several performance
“upgrades” that increase the BSE, such as lowered
springs, stiffer
springs, low profile and/or wider tires, some aftermarket A-arms and
some aftermarket LCAs. NOTE: I am not saying that
if you
install the above-mentioned “negative effect” parts
on your car, that
you will have horrific BSE and handling. What I am saying is
that
these parts have been shown to aggravate the BSE on vehicle with
MBS. The more modifications you can make that reduce MBS and
or
the BSE and the fewer modifications you make that increase MBS and or
the BSE, then, it stands to reason, the better the car will steer and
hold the road.
Ways
to reduce Measurable Bump-Steer (MBS), the
Bump-Steer
Effect (BSE), and why
Bump-Steer
Kit: As we have
discussed earlier Bump-Steer
is a geometric defined phenomenon that is present or it
isn't. A
Bump-Steer kit is the only way, short of major steering and suspension
modifications, to truly eliminate the problem. As I mentioned
before, there is positive and negative Bump-Steer. However,
for
all intents and purposes, positive Bump-Steer is the occurrence on most
vehicles. That means that to truly cure it, the only option
is to
lengthen the tie rod assembly. The problem with this
“solution”
is that, without other modifications, lengthening the tie rod assembly
will take the car out of alignment. That is where the advent
of
the Bump-Steer kit comes into play. A Bump-Steer kit is an
adjustable mount that lowers the connecting point of the outer tie rod
and the spindle steering arm. By lowering the connecting
point,
you are able to lengthen the tie rod assembly and, thus, increase the
tie rod arc, but still maintain the toe setting. The following (non
proportional) picture illustrates how a Bump-Steer kit
works. The
blue represents the kit, which typically consists of a stud that drops
down below the steering arm and a special connector that allows said
stud to connect to the outer tie rod. The red represents the new angle
of the tie rod assembly and the green represents the amount the tie rod
needs to be lengthened to accommodate the Bump-Steer kit.
Installing a Bump-Steer kit is simple. Calibrating it, on the
other hand, is not! To calibrate a Bump-Steer kit you must
take
many measurement with the suspension in fully extended and fully
compressed positions, which means that things like coil springs need to
be removed prior to adjustment. Also, as with other
adjustments
in alignment, the toe and the Bump-Steer kit need to be adjusted at the
same time because they affect each other. It is this
challenge in
alignment and adjustment that makes a Bump-Steer kit a non-option for
many car enthusiasts, because most alignment shops will not align a car
with a Bump-Steer kit and the individual car owners do not have the
equipment or skills required to align their car themselves.
It is
for this reason that treating the symptom rather than the
cause,
for many car enthusiasts, is a more feasible option.
Shelby
Drop: The
Shelby Drop is not only effective in
the reduction of the BSE, but is easily the most cost
effective
and one
of the most over all effective Mustang suspension upgrades.
The
beauty of it is that, other than time and tools required to perform the
modification, there is no out of pocket expense. The Shelby
Drop
works by improving the camber curve which improves the contact between
the tires and the
road. Changing the camber curve will slightly increase MBS
however that small increase in MBS is far outweighed by the
improved handling and a decrease in the BSE. The Shelby drop
also
lowers the center of gravity on the front suspension, which
decreases body roll. Keep in mind that even though the drop
is 1"
the actual change in ride height is only 1/4" to 5/8".
Information on performing this suspension modification, as
well as ordering information for steel Shelby Drop templates, can be
found at the UCA
Drop page on www.DazeCars.com and ordering information for
steel templates can be found on my For
Sale Page.
When performing a
Shelby Drop, the UCA needs to be removed and this provides a
natural opportunity to upgrade the rubberized spring perches to roller
spring perches.
Roller
Spring Perches: Improving
suspension response time and
also freeing up desirable motion in the upper A-arm springs and shocks
is very effective in the reduction of the BSE. Many vintage
Ford
cars use spring perches bolted to the upper A-arm that serves as a
bottom resting point for the coil springs. The design of the
spring perch, through its ability to rotate back and forth as the A-arm
travels up and down, allows the coil spring to move with more
consistent vertical travel through compression and
decompression.
The original spring perches found on the early Falcons had brass
bushings. This allowed for a smooth rotation but had the
downside
of needing regular greasing due to considerable friction between the
surface of the bushing and the journal it rested in. For this
reason, as well as to cut costs FoMoCo decided to replace the brass
bushings with rubber ones. Although cheaper to produce, the
rubber bushing spring perches lack the smooth, easy turning radius
afforded by the brass bushing. If you have ever
tried to
turn the center shaft in a rubber bushing spring perch, you
know
that it takes quite a bit of force to get any movement. This excess
force required for movement oftentimes causes unwanted flexing of the
springs and shocks and results in a less than consistent, less-vertical
travel during suspension compression and decompression. One
option in correcting this issue is to replace the rubber bushing with
aftermarket brass bushings, returning the perch to the initial Ford
design. This works well, but without regular greasing, brass
bushings tend to squeak. Another option is to create the
roller
spring perch. By replacing the rubber bushings with roller
bearings, a smooth turning radius can be achieved and, thus, smoother
suspension and drivability without the added friction and squeaking of
a brass bushing. More information on Roller Spring Perches,
as
well as information on building your own or purchasing a completely
fabricated set can be found at www.DazeCars.com, “Opentracker"
Roller Spring
Perches. Once the front suspension has been removed
and
reinstalled due to the replacement of the vehicle’s spring
perches, it
is important to have the suspension realigned.
Performance
Alignment:
A
performance
alignment, even without
all of the other suspension modifications, can be a very effective
means of reducing the BSE. The problem with a stock alignment
is
that it is done to Ford’s original specifications and,
frankly, those
specifications are not conducive to performance. The settings
that you should set your Mustang’s suspension to are:
0 to -.5 degrees of Camber but can be as much as -3 degrees Camber for
the track cars
1/16 to 1/8" toe in
+1.5 to +3 degrees of Caster but as much as 5 degrees Caster for the
track cars
These
Camber
settings allow the maximum
rubber to road engagement without excessive scrubbing of the
tires. Camber setting more extreme than -.5 will increase
handling, but at the expense of rapid tire wear. The more
rubber
you have in contact with the pavement, the more accurately the steering
will be. The toe setting allows the tires to spread as you go down the
road so that when you are driving, the forward pressure brings the toe
to 0. If you started with a toe setting of 0, the forward
pressure as you are going down the road will cause your tire to end up
toeing out. Caster is the big one when dealing with the
BSE. The more Caster you have, the quicker your wheels return
to
a centered forward position. That means that, due to road
condition, when MSB occurs, the quick returning to center of the
steering will minimize the BSE. A car with significant amounts of
Caster will track and hold the road much better than a car with less
Caster. Caster is one of our best weapons against the
BSE.
That is the biggest reason adjustable strut rods are a natural choice
when dealing with the BSE because it allows us to increase the caster
further than the shims can. The following account regarding
the
BSE and a performance alignment is from John Dinkel AKA Opentracker of Opentracker
Racing Products:
"A
guy I know has
a daughter with a 66 Coupe. They started working on it about 5 years
ago. They installed Granada discs, a sway bar, shocks and other
suspension mods. (Nothing too trick) The car drove like crap when they
got it on the road. It would rise at highway speeds and wander all over
the road. For 5 years, they could only drive the car around town. They
tried all kinds of things to fix it, including having it re-aligned
three times by local shops. I got a call to look at the car. It sounded
like Bump-Steer to everyone else and their next plan was to put on a
Bump-Steer kit. I asked who had done the alignments. The shops they had
used set the cars to factory settings. I told them to have the car
aligned again (they thought I was off my rocker) but it worked. They
can now drive the car 100mph if they want. No wander and no rise at
speed. The factory settings say the car only needs 1 deg of positive
caster and 1 deg of positive camber. Positive camber!! I had them set
the car to 0 to .5 neg, camber and 2.5 deg pos. caster with 1/8" toe
in. The owner was so happy he couldn't hold himself together.
Before the performance alignment his daughter was ready to sell the car
after all the work they had done because it was so hard to drive. Now
she drives it every day and loves it. "
Also,
when having
your car aligned, keep
in mind that a typical alignment shop will not correct for MBS,
because, one, they do not check for it and, two, they do not have a way
to adjust it. Like I mentioned before, the simple act of
adjusting the toe will affect MBS. The original designers
knew
this and designed the steering and suspension to absorb the effect,
that way, even though small amounts of MBS are present, the effect is
not felt. To put it simply, a performance alignment improves
the
suspension and steering ability to absorb the BSE and hold the road
better. Lastly, when it comes to alignment, factory
tolerances
allow small differences in the setting between the driver’s
and
passenger’s sides. This is to reduce the time it
takes to do the
alignment. It is extremely important that the alignment
specifications be as close as possible on both sides of the car which
will make the alignment take longer and probably cost more.
For
this reason make sure you take your car to an alignment shop you
trust!!!
Adjustable
Strut Rods: By
eliminating
unwanted suspension
movement and maximizing desirable suspension movement the BSE can be
reduced. Adjustable strut rods are an obvious choice in this
respect, due to their incredible ability to improve suspension and
handling. The function of the strut rod in a classic Mustang is to
stabilize the lower control arm in a fixed position that prevents its
movement forward and aft, but still allows it to travel vertically with
suspension compression and decompression. The stock system is designed
so that, during regular driving, the rubber bushing gives, allowing
vertical travel as the lower control arm moves up and down.
The
give in the bushings, unfortunately, has a negative side effect of
unwanted movement, as they compress and stretch during braking and
acceleration. The result of the compression and stretching of the
rubber bushings is an increase and decrease in the length of the strut
rod. As the strut rod increases and decreases in length, the lower
control arm is not held fixed and can move forward and aft a small
amount, which puts the alignment in a constant state of change during
driving. The challenge is to have a joint that freely moves
vertically, but is also fixed in such a way that it cannot shift
forward or aft. This can be easily accomplished by using a heim joint
at the bushing end of the strut rod. An added benefit of a
heim
joint system is that, by having two threaded ends with opposite thread
directions, one on the heim joint and one at the base of the strut rod,
you can use a threaded connecting tube and make the strut rods
adjustable for an easier and more fine tuned alignment. More
information on Adjustable Strut rods as well as information on building
you own set or purchasing a completely fabricated set can be found at
www.DazeCars.com, Adjustable
Strut Rods.
Granada
Disc Brakes on an early Mustang:
Granada
disc
brakes are a popular
upgrade to the classic Mustang due to affordability and availability of
parts. If the Mustang they are being installed on is a
‘67 or
newer, then the swap is very effective because the geometry of the
Granada and stock Mustang spindles are identical, which means there is
no change in MBS or the BSE. However, if the Granada discs
are
being installed on an early Mustang ‘64 &
1⁄2 to ‘66, then,
due to a different location of the spindle steering arm, MBS is
increased. It makes sense that both MBS and the BSE would be
an
issue when installing Granada disc brakes on an early Mustang because
one of the steps in this process is to shorten the adjusting sleeves,
as well as the inner and outer tie rod ends. If this modification is
not made then the tie rod ends bottom out in the adjusting sleeve and
there is not enough adjustment to correctly set the toe when performing
an alignment. As I demonstrated earlier, one of the two defining
measurements of MBS is the arc of the outer tie rod, which is a direct
result of tie rod length. All this said, it stands to reason
that
by making the tie rod assembly shorter than it was originally designed
to be, MBS would be increased. This explains why the best
option
when dealing with MBS is to utilize factory components. That
means stock Mustang spindles of the same year as the vehicle are the
most ideal option. If you want to put disc brakes on your
stock
spindles, you have several options. The first option is
original Mustang disc brake
components, which can be purchased and installed on your
original V8 drum
brake spindles. Second, there are options such as the Mustang
Steve
Cobra disc set up which allows you to put Cobra disc brakes
on original
V8 spindle. I have also seen similar kits that use "bowtie"
parts. A third option, is disc brakes from CSRP
There you will find kits based on the Granada disc brake configuration
so replacement parts are plentiful and inexpensive. What is different
about this swap and the original donor car Granada conversion is that
the
spindles are new and because of that there are spindles available that
have been reengineered to maintain the correct 1964.5 - 1966 steering
geometry.
Personal Experience with Granada
Discs on a
64 & 1⁄2 Mustang:
There
has been a
movement as of late
away from using Granada discs on an early Mustang, and some of this
movement is for good reason. However, much of this movement
has
been perpetuated from horror stories of individuals who claim (due to
the experience with their own individual cars) that no early Mustang
with Granada disc brakes will steer properly and, due to
“Bump-Steer”,
the car will be difficult to keep on the road at low speeds and
impossible to keep on the road at high speeds. I am here to
tell
you that with moderate modifications and performance up-grades this is
simply not the case. I have a 64 & 1⁄2
Mustang with
Granada discs and I have yet to feel any BSE after installing my
Granada discs and some performance suspension parts. In fact,
I
live in MT where many of the roads are filled with bumps and potholes
and, due to this fact, have put my car through some extreme suspension
travel, and yet I still have not felt any BSE. Ironically, my
car’s steering was far more erratic before I installed the
Granada
discs and the suspension up-grades, especially at high speeds when
changing lanes so as to pass. My current front end
suspension,
steering, and braking combination consists of: 6 cyl steering linkage,
Granada disc brakes, GT springs, KYB shocks, Roller Spring Perches,
1”
Shelby Drop, Adjustable Strut Rods, a 1” sway bar and a
moderate
performance alignment. My car handles like it is on rails at
all
speeds. If you are interested in installing Granada
disc
brakes on your car, you have several options. Some Mustangs
will
accept Granada tie-rod ends, making the
swap simple.
However, for other Mustangs, such as 6 cyl Mustangs, this is not an
option. MustangSteve has the solution in his Granada disc
brake Tie
Rod Bushings. He also has a very informative page
on the ins
and outs of Putting
Granada disc brakes on a Mustang.
Final
thoughts:
Keep
in mind that
every car has its own
personality, that is to say what is the perfect solution on one car may
not be as effective on another, even if they are the same year, make
and model, it is my hope, however, that the info I have provided on MBS
and BSE can be generally applied to our cars so that suspension
performance and handling can be improved. Other than dealing
with
actual MBS, there is no clear-cut answer. Our only options
are to
use the info I have outlined, a little common sense and some trial and
error to come up with the best possible handling package.
Disclaimer on Daze Tech Tips
I am not an expert
in this field. I have performed these modifications myself with very
good results. I am passing along restoration and
performance tips for the purpose of education. If you are
concerned about reliability or safety issues, I do not recommend that
you or any other individual perform these changes or attempt to modify
your cars from stock configuration except under your own
volition. I do not assume nor accept any liability for the
use of
this
information or how it is applied.
By
eliminating
unwanted suspension
movement and maximizing desirable suspension movement the BSE can be
reduced. Adjustable strut rods are an obvious choice in this
respect, due to their incredible ability to improve suspension and
handling. The function of the strut rod in a classic Mustang is to
stabilize the lower control arm in a fixed position that prevents its
movement forward and aft, but still allows it to travel vertically with
suspension compression and decompression. The stock system is designed
so that, during regular driving, the rubber bushing gives, allowing
vertical travel as the lower control arm moves up and down.
The
give in the bushings, unfortunately, has a negative side effect of
unwanted movement, as they compress and stretch during braking and
acceleration. The result of the compression and stretching of the
rubber bushings is an increase and decrease in the length of the strut
rod. As the strut rod increases and decreases in length, the lower
control arm is not held fixed and can move forward and aft a small
amount, which puts the alignment in a constant state of change during
driving. The challenge is to have a joint that freely moves
vertically, but is also fixed in such a way that it cannot shift
forward or aft. This can be easily accomplished by using a heim joint
at the bushing end of the strut rod. An added benefit of a
heim
joint system is that, by having two threaded ends with opposite thread
directions, one on the heim joint and one at the base of the strut rod,
you can use a threaded connecting tube and make the strut rods
adjustable for an easier and more fine tuned alignment. More
information on Adjustable Strut rods as well as information on building
you own set or purchasing a completely fabricated set can be found at
www.DazeCars.com, Adjustable
Strut Rods.
As we have
discussed earlier Bump-Steer
is a geometric defined phenomenon that is present or it
isn't. A
Bump-Steer kit is the only way, short of major steering and suspension
modifications, to truly eliminate the problem. As I mentioned
before, there is positive and negative Bump-Steer. However,
for
all intents and purposes, positive Bump-Steer is the occurrence on most
vehicles. That means that to truly cure it, the only option
is to
lengthen the tie rod assembly. The problem with this
“solution”
is that, without other modifications, lengthening the tie rod assembly
will take the car out of alignment. That is where the advent
of
the Bump-Steer kit comes into play. A Bump-Steer kit is an
adjustable mount that lowers the connecting point of the outer tie rod
and the spindle steering arm. By lowering the connecting
point,
you are able to lengthen the tie rod assembly and, thus, increase the
tie rod arc, but still maintain the toe setting. The following (non
proportional) picture illustrates how a Bump-Steer kit
works. The
blue represents the kit, which typically consists of a stud that drops
down below the steering arm and a special connector that allows said
stud to connect to the outer tie rod. The red represents the new angle
of the tie rod assembly and the green represents the amount the tie rod
needs to be lengthened to accommodate the Bump-Steer kit.
Installing a Bump-Steer kit is simple. Calibrating it, on the
other hand, is not! To calibrate a Bump-Steer kit you must
take
many measurement with the suspension in fully extended and fully
compressed positions, which means that things like coil springs need to
be removed prior to adjustment. Also, as with other
adjustments
in alignment, the toe and the Bump-Steer kit need to be adjusted at the
same time because they affect each other. It is this
challenge in
alignment and adjustment that makes a Bump-Steer kit a non-option for
many car enthusiasts, because most alignment shops will not align a car
with a Bump-Steer kit and the individual car owners do not have the
equipment or skills required to align their car themselves.
It is
for this reason that treating the symptom rather than the
cause,
for many car enthusiasts, is a more feasible option.
The
Shelby Drop is not only effective in
the reduction of the BSE, but is easily the most cost
effective
and one
of the most over all effective Mustang suspension upgrades.
The
beauty of it is that, other than time and tools required to perform the
modification, there is no out of pocket expense. The Shelby
Drop
works by improving the camber curve which improves the contact between
the tires and the
road. Changing the camber curve will slightly increase MBS
however that small increase in MBS is far outweighed by the
improved handling and a decrease in the BSE. The Shelby drop
also
lowers the center of gravity on the front suspension, which
decreases body roll. Keep in mind that even though the drop
is 1"
the actual change in ride height is only 1/4" to 5/8".
Information on performing this suspension modification, as
well as ordering information for steel Shelby Drop templates, can be
found at the 
Improving
suspension response time and
also freeing up desirable motion in the upper A-arm springs and shocks
is very effective in the reduction of the BSE. Many vintage
Ford
cars use spring perches bolted to the upper A-arm that serves as a
bottom resting point for the coil springs. The design of the
spring perch, through its ability to rotate back and forth as the A-arm
travels up and down, allows the coil spring to move with more
consistent vertical travel through compression and
decompression.
The original spring perches found on the early Falcons had brass
bushings. This allowed for a smooth rotation but had the
downside
of needing regular greasing due to considerable friction between the
surface of the bushing and the journal it rested in. For this
reason, as well as to cut costs FoMoCo decided to replace the brass
bushings with rubber ones. Although cheaper to produce, the
rubber bushing spring perches lack the smooth, easy turning radius
afforded by the brass bushing. If you have ever
tried to
turn the center shaft in a rubber bushing spring perch, you
know
that it takes quite a bit of force to get any movement. This excess
force required for movement oftentimes causes unwanted flexing of the
springs and shocks and results in a less than consistent, less-vertical
travel during suspension compression and decompression. One
option in correcting this issue is to replace the rubber bushing with
aftermarket brass bushings, returning the perch to the initial Ford
design. This works well, but without regular greasing, brass
bushings tend to squeak. Another option is to create the
roller
spring perch. By replacing the rubber bushings with roller
bearings, a smooth turning radius can be achieved and, thus, smoother
suspension and drivability without the added friction and squeaking of
a brass bushing. More information on Roller Spring Perches,
as
well as information on building your own or purchasing a completely
fabricated set can be found at www.DazeCars.com, 
