Tom Wilson
May 2, 2014

Horse Sense:
These days Maximum Mustang caster/camber plates carry a lifetime warranty—something of a rarity for aftermarket parts, which speaks volumes about their durability.

So, you put lowering springs in your Mustang and now the alignment shop has called saying they can't get the camber where it needs to be and you need a set of camber plates. What are those?

Caster/camber plates are a popular, but often-ignored Mustang bolt-on. Obviously, they allow adjustment of front-end alignment, but the details of just what caster/camber plates adjust, how they are built and installed often seem murky. To get the straight scoop we traveled to Maximum Motorsports, who are, if not the sole inventor of this alignment device, are definitely the major developer and seller of the caster/camber plate as we've known it for the last 20 years.

Since the first Fox Mustangs roamed the planet, they have had a MacPherson strut front suspension. It's an economical layout employing an over-sized shock absorber—the strut—in a dual role as both suspension damper and suspension locating device. The strut is attached to the lower control arm (via the steering spindle) at the bottom, and the chassis at its top. In fact, the round bump in the engine compartment where the strut bolts to the body is called the strut tower, and it's at the top of the strut tower where the caster/camber plate reigns.

Because the strut defines the top location of the suspension geometry it is a major player in setting the suspension's alignment. Specifically, moving the top of the strut toward or away from the center of the car adjusts camber while moving the top of the strut forward and backward along the length of the car determines caster.

One characteristic of the Fox front suspension chassis tuners soon came to understand was it did not have enough caster. Because camber and caster are interconnected, maximizing camber cost desirable negative camber when the front tires were steered away from center just when negative camber is needed—while cornering.

When a strut Mustang's ride height is lowered—think lowering springs—negative camber is increased to harmful levels on street cars. Thus, the typical Fox enthusiast who was driving hard in the corners needed some help increasing caster, and if his car was lowered, he needed help in regaining the stock Ford camber setting as well.

In the mid-'80s, Global West was the first to offer a bolt-on solution with their caster plates. These allowed adjusting in increased in caster, but they were not easily adjustable for camber. Instead, Global West offered two versions of their plate; the Street version yielded stock Ford camber, the Race version delivered increased negative camber for track cars, but in either case the camber was not readily adjustable.

Caster/camber plates provide the same basic alignment function on all Mustangs, but different Mustang chassis have different alignment needs. An S197 such as this has all the caster it could ever use on a race track while sitting on the showroom floor, for example. But it could definitely use more camber if taken to the track. A lowered Fox needs both increased caster and reduced negative camber if street driven.
This is the kit that started it all (PN MMCC7989) for ’79-’89 Mustangs. The key concept is that the flat, vaguely triangular-shaped plates set camber, while the bearing retainer with the Teflon-sealed spherical bearing and two studs set caster. Maximum notes it started buying bearings 5,000 at a time when the supplier offered the exact size desired, eliminating the need for a sleeve used previously. The black cones are bumpstops to help with lowered cars.
When Ford changed the Fox caster specification in 1990, it also changed some strut-top hardware, including the strut tower itself. This required subtle length and slot changes to the Maximum main plate, as shown by the ’79-’89 plates at top and ’90-’93 plates in the bottom row. Passenger-side plates are to the left. It’s possible to file the later strut towers to allow the earlier caster/camber plates, but they’ll sit askew to the tower and don’t give the same range or ease of adjustment. Mixing up early and late Fox caster/camber plates is a typical swap-meet problem, so beware.
Matching the early and late Fox main plates are these ’79-’89 (left) and ’90-’93 (right) bottom plates. The physical differences are too subtle to see, just a 1⁄8-inch movement in the studs, but it’s enough that the plates are not interchangeable. To keep things sorted, Maximum gives the ’90-’93 plates an identifying notch, seen on the right-hand edge here.
Conceptually identical to Fox plates, Maximum’s MMCC9994 plates for ’94-’04 Mustangs differ mainly in they use a four-bolt mount. This means drilling one hole in the strut tower, but the payoff is a vastly stronger plate that will not bend under anything less than crash conditions.

In the later '80s, Central Coast Mustang released a similar plate that gave a fixed caster—greater than stock—and fixed camber, again in two positions for either stock or lowered ride heights. Then, in 1993, Maximum Motorsport introduced the fully adjustable caster/camber plate. This is the now-familiar two-plate device that allowed adjusting caster and camber independently of each other, and gave a larger range of adjustment than Ford provided. The Maximum caster/camber plate was an instant success and has been copied many times, but never really improved upon.

Unfortunately for Maximum Motorsport, its original two-plate design was not patented—the company didn't have the money at the time for the application fee—so the concept was an open source from the beginning. Later Maximum designs are patented and offered by nearly everyone.

Of course, as Ford developed the Mustang, changes to the camber plates were necessary. Up to 1989, the Fox shock tower and camber plate was mainly unchanged, but in 1990, Ford dialed in a bit more caster (but not enough), relocating the strut-mount holes in the shock tower in the process. Many enthusiasts and some shops missed this unannounced change. Maximum, which opened for business in 1992, discovered the difference immediately while researching its original plate design, and has always offered early and late Fox caster/camber plates.

When the SN-95 Mustang debuted in 1994, it required yet another variation of the caster/camber plate from Maximum. It was similar in concept to the Fox plate, but not interchangeable.

A big change came in 1999, when Maximum added a fourth mounting bolt to its caster/camber plate. The three-bolt plates using Ford's original bolt pattern would bend under extreme pounding with coilovers, or when accidentally taken off-track at speed during spins, or as crash avoidance. The issue, found only on SN-95s, was that Ford's three-bolt pattern left the upper strut tower cantilevered off to one side with track suspension settings, overloading the plates. The solution was boxing the upper strut with a fourth plate stud. This required drilling a fourth hole in the strut tower for the new stud to pass through, but doing so increased strength greatly. The new SN-95 four-bolt caster/camber plates made the previous three-bolt units obsolete, so Maximum discontinued the earlier design for SN-95s. Fox Mustangs have never needed or had a four-bolt plate from Maximum.

When the S197 Mustang debuted in 2005, its all-new, completely non-adjustable, four-bolt upper strut mount required an entirely new plate from Maximum. Maximum's design used the same two-plate, four-bolt concept of its earlier caster-camber plates, but mounted inside the strut tower. Thus, the current Mustang's caster/camber plate from Maximum is not visible from underhood, but it does give the necessary adjustment to account for chassis aging, crash damage, and, of course, lowered ride heights from lowering springs, along with performance alignment specifications.

In 2011, Ford significantly modified the grip and thread lengths of the upper mounting threads on the struts used in the garden variety V-6 and Mustang GTs, while leaving the GT500 and FRPP struts alone. This meant Maximum had to develop two caster/camber plates for '11-and-later Mustangs, and customers had to know which struts they have on their cars. In the meantime, Maximum is working on a third S197 caster-camber plate that will work with all variations of the S197 struts. Look for the new plate later this year.

There are more details in the photos, along with a review of caster/camber plate installation, on both Fox/SN-95 and S197 chassis. Just remember caster/camber plates have a specific job, and different Mustang chassis have different need of their services.

Showy types have prompted Maximum to offer chrome plated caster/camber kits for pre-S197 cars. Just the main plates get the shiny treatment, which looks good with Maximum’s normal cad-plated hardware. To order a chrome kit put a –C after the normal Maximum part number.
Putting a stock Ford SN-95 upper strut mount next to Maximum’s lower plate for the same application best shows why Maximum’s four-bolt solution was necessary on SN-95s. On the black mount, the three studs form a triangle, but the center hole, which represents where the strut top passes through, can be just outside one leg of the triangle. This overloads two of the studs and bends plates under extreme loads. The four-bolt solution easily boxes the strut inside a rectangle, more evenly spreading the loads. On Foxes the stock three-bolt “triangle” always captures the upper strut, so a four-bolt Fox plate is not necessary.
Maximum’s S197 kit won’t be confused with the SN-95 or Fox offerings as the hardware is completely different. All but the kidney-shaped support plates at bottom end up hidden inside the strut tower with these plates.
Ford uses a ball-bearing upper spring perch on S197s. Most owners know these as the source of a popping or graunchy noise when they often fail from dirt intrusion. Maximum replaces the ball bearing with a pair of sliding plastic discs in their upper spring perches shown here. They have proven more durable, and silent.
In 2011, Ford ambushed everyone by shortening the upper strut shaft and altering the non-threaded grip length on Mustang GT and V-6 struts, while leaving the Shelby GT500 and catalog-only FRPP struts at the old spec. This requires different caster/camber plates, as shown by the early all-Mustang S197 strut at left and the ’11-and-later GT/V-6 strut at right. Maximum is working on a universal kit.
There are a surprising number of Ford applications with minor strut or tower differences affecting caster/camber plate installation, and Maximum has them all covered. This is the kit for ’03-‘04 Cobras (PN MMCC0304), which came from Ford with Bilstein struts. Because these Bilsteins have internal bumpstops, Maximum deletes its black cone-shaped bumpstops, as found in the V-6/GT kit, and adds the necessary blue dust bellows at right. This is also a handy kit for those retro-fitting Bilsteins to ’99-’04 Mustang GTs.

Caster & Camber

Don't feel bad if alignment specs aren't your strong suit; most performance fans are weak on suspension tuning.

Camber is perhaps the easier concept. It is the lean the tire takes when seen from the front or rear of the vehicle. If the top of the tire leans toward the center of the car that is negative camber; if the top leans outward compared to the bottom of the tire that is positive camber.

Some negative camber is desirable because the combination of tire construction and suspension movement means about one degree of negative camber translates into nearly zero or neutral camber at the outside front tire when cornering. This presents the tire tread flat to the pavement, maximizing grip and minimizing wear.

How much negative camber is wanted depends on how and where the vehicle is driven. On the street little negative camber is needed because most of the time the car drives straight ahead or is cornered gently. Maybe one degree of negative camber is best. Add in more and the tire wears unevenly (and rapidly), and the steering can be a little darty because a tilted tire wants to roll in a circle, not a straight line. That will tug on the steering as the suspension extends and compresses over bumps, even as the vehicle moves in a straight line.