With the introduction of solid metal and nylon suspension bushings from mc
˛racing,
the answer to the question "which bushings should I use" is becoming more and more complex. There are now five
materials being used to manufacture stock-style suspension bushings - stock rubber, Group N rubber, polyurethane, nylon,
and aluminum. Here are some thoughts on each material as they apply to suspension bushings.
Stock rubber
This is the rubber that is used to manufacture the bushings that were originally equipped on your vehicle. Stock rubber
easily compresses, which allows for a soft ride since shocks caused by road features (potholes, etc) are readily
absorbed. Unfortunately, bushings that easily compress lead to unwanted toe and camber deflection. Additionally, since
rubber is fused to the inner sleeve, pivot bushings made of rubber twist rather than rotate, which basically adds tons
of friction to the suspension, decreasing response time. This has a similar effect to increasing the unsprung mass of
the car. Stock rubber is only suitable for numbly-driven unmodified vehicles.
Group N rubber
This rubber was designed for FIA Rally classes that require the use of rubber suspension bushings. They are much
stiffer than stock rubber, which yields a slightly harsher ride via increased transmission of road feature shocks. The
good news is that the decreased compressibility reduces toe and camber deflections (which is why Group N rubber was
designed in the first place). However, this material is still fused to the inner sleeve, so the twisting "friction"
problem still exists. In fact, since Group N rubber is stiffer than stock rubber, the amount of force required to
displace the suspension from rest is greatly increased over stock, which means that your suspension will be less
responsive than it was straight out of the factory! Group N rubber is a good choice on daily-driven vehicles for
non-pivoting bushings such as the differential mount, the rear beam mounts, and the power steering rack bushings.
We're sad to report that long ago we purchased and sold the last of the Group N beam mount and Group N
differential mount bushings in existence, as Ford rendered these bushings "NLA".
Polyurethane
This material is similar in stiffness to Group N rubber, but since it is not fused to the inner sleeve, the twisting
"friction" effect is greatly reduced. For this reason, polyurethane-equipped suspensions will out-perform Group N
rubber-equipped suspensions by being more responsive. The polyurethane does stick to the inner sleeve a little, so
the twisting "friction" still exists, albeit much less than with rubber. The ride harshness will naturally be similar
to Group N. The down side to polyurethane bushings is the potential for squeaking since the bushing material rotates
about the inner sleeve. Polyurethane bushings must be lubricated with grease periodically to prevent this phenomenon.
Some polyurethane bushing manufacturers, such as Powerflex, use a graphite-impregnated matrix. This basically makes
the grease "built-in", eliminating the necessity to periodically grease the bushing. By all means graphite-impregnated
polyurethane bushings are the only kind of polyurethane bushing to purchase.
There are a few methods used to manufacture polyurethane bushings, including injection molding, open casting, and
compression molding. Each method can also include a post-pour oven bake. Because of the variety of methods used to
manufacture them, not all polyurethane bushings are created equal. The general rule of thumb when purchasing
polyurethane bushings for a Merkur is to purchase Powerflex. The polyurethane bushings available "unlabelled" are
well-known for squeaking, and Deflex bushings are well-known for having terrible tolerance control. In particular,
it is very well documented that Deflex bushings have terrible quality control on their outer TCA and rear beam mount
bushings, which are two of the most important bushings on the car. We all know that the outer TCA bushings control
commonly-experienced vibrations at speed, and the rear beam mount bushings basically control the entire rear
suspension. Additionally, since Powerflex uses stainless steel sleeves instead of mild steel like the others, there
is only one choice in polyurethane bushings.
Nylon
Nylon is a very stiff material that can be considered for all intents and purposes to be solid. It effectively
eliminates toe and camber deflections, and it effectively eliminates twisting "friction" at the pivot point. Ride
harshness will be maximized with the use of nylon bushings. Some nylon bushing manufacturers, such as
mc
˛racing, use a lubricant-impregnated matrix to prevent squeaking since nylon bushings
do rotate about the inner sleeve rather than twisting. Unlike rubber and polyurethane, nylon bushings must be
machined to very tight tolerances, which makes them about five times more expensive to manufacture.
Aluminum
Aluminum is a very stiff material that can be considered for all intents and purposes to be solid. It effectively
eliminates toe and camber deflections, and it effectively eliminates twisting "friction" at the pivot point. Ride
harshness will be maximized with the use of aluminum bushings. Lubricant-impregnated aluminum is basically
unavailable, so an aluminum bushing much be greased often if used at a pivot point. With the availability of
lubricant-impregnated nylon bushings, there is little reason to use aluminum for any pivot point bushing. However,
aluminum is a great choice for non-pivoting bushings such as the differential mount, the rear beam mounts, and the
power steering rack bushings. Unlike rubber and polyurethane, aluminum bushings must be machined to very tight
tolerances, which makes them about five times more expensive to manufacture.
Bushing Selection
So what bushings should you select for your car? First let's assume that you are using the stock suspension arms.
Below is a list of of bushings and a recommendation for which type of vehicle they can be used on. This list is
pretty straightforward, but there is one caveat to keep in mind. On vehicles where ride harshness is a concern, a
very stiff bushing can still be used at the rear of the car. For example, if nylon bushings are installed in the
semi-trailing arms (STAs), the road shocks will be transmitted to the rear beam. Since the rear beam is isolated
from the chassis by the beam mount bushings and the rear differential mount, the driver will continue to experience
a nice ride. Whereas it may seem like a Merkur-specific treat to be able to run a solid bushing on a daily-driven
street car, the fact that the rear wheels are controlled by two sets of bushings is ultimately a negative. The STAs
can flex about the beam, and the beam can flex about the chassis. This is why even polyurethane or Group N rubber
are
totally unsuitable to controlling the rear suspension on a performance Merkur.
|
TCA Inner Bushings
|
| Material |
Recommended Application |
| Ford Stock Rubber | Concours restoration |
| Ford Group N Rubber | Daily-driver, high-perf street, mild track, race |
| Deflex Polyurethane | Not recommended |
| Powerflex Polyurethane | Daily-driver, high-perf street, mild track, race |
| mc˛racing Machined Nylon | Discontinued |
|
|
TCA Outer Bushings
|
| Material |
Recommended Application |
| Ford Stock Rubber | Concours restoration |
| Ford Group N Rubber | Daily-driver, high-perf street, mild track, race |
| Deflex Polyurethane | SERIOUSLY not recommended! |
| Powerflex Polyurethane | Daily-driver, high-perf street, mild track, race |
|
|
Front Sway Bar Bushings
|
| Material |
Recommended Application |
| Ford Stock Rubber | Concours restoration |
| Deflex Polyurethane | Not recommended |
| Powerflex Polyurethane | Daily-driver, high-perf street, mild track, race |
|
|
Upper Strut Mount Bushings
|
| Material |
Recommended Application |
| Ford Stock Rubber | Concours restoration |
| Ford Group N Rubber | Daily-driver, high-perf street, mild track, race |
| Deflex Polyurethane | Not recommended |
| Powerflex Polyurethane | Daily-driver, high-perf street, mild track, race |
|
|
Steering Rack Bushings
|
| Material |
Recommended Application |
| Ford Stock Rubber | Concours restoration |
| Generic Polyurethane | Not recommended |
| mc˛racing Machined Nylon | Daily-driver, high-perf street, mild track, race |
|
|
STA Outer Bushings
|
| Material |
Recommended Application |
| Ford Stock Rubber | Concours restoration |
| Ford Group N Rubber | Not recommended |
| Deflex Polyurethane | Not recommended |
| Powerflex Polyurethane | Not recommended |
| mc˛racing Machined Nylon | Daily-driver, high-perf street, mild track, race |
|
|
STA Inner Bushings
|
| Material |
Recommended Application |
| Ford Stock Rubber | Concours restoration |
| Ford Group N Rubber | Not recommended |
| Deflex Polyurethane | Not recommended |
| Powerflex Polyurethane | Not recommended |
| mc˛racing Machined Nylon | Daily-driver, high-perf street, mild track, race |
|
|
Rear Sway Bar Bushings
|
| Material |
Recommended Application |
| Ford Stock Rubber | Concours restoration |
| Deflex Polyurethane | Not recommended |
| Powerflex Polyurethane | Watch out for incorrect bushing "height" |
|
|
Rear Beam Mount Bushing
|
| Material |
Recommended Application |
| Ford Stock Rubber | Concours restoration |
| Ford Group N Rubber | Discontined |
| Deflex Polyurethane | SERIOUSLY not recommended! |
| Powerflex Polyurethane | Daily-driver, high-perf street |
| mc˛racing Solid Weld Kit | Mild track, race. Requires solid diff mount |
| mc˛racing Machined Aluminum | Discontinued |
|
|
Rear Differential Mount
|
| Material |
Recommended Application |
| Ford Stock Rubber | Concours restoration |
| Ford Group N Rubber | Discontined |
| mc˛racing Polyurethane | Daily-driver, high-perf street |
| mc˛racing Solid Aluminum | Mild track, race. Requires solid beam weld kit |
|