Modifying our Mustangs often involves trade-offs: adding top-end horsepower could sacrifice low-end torque, a high-flow exhaust may bludgeon your eardrums, and a stiffer suspension can be just that--stiff.
Well, not so fast. After installing a Maximum Motorsports coilover suspension on an '03 Mustang Cobra, we're rethinking that last assumption.
The '79-'04 Mustang's "modified...
The '79-'04 Mustang's "modified MacPherson strut" suspension puts a lot of force on the control arm bushings and ball joint. For example, a 3,500-pound car has roughly 1,000 pounds on each front wheel. Because of its location, the spring supports the car's weight with 2,000 pounds of force on the control arm, and 1,054 pounds of force on the control arm bushings and ball joint. All this force on the control arm bushings and ball joint creates friction, which hinders the suspen- sion's ability to move and absorb bumps, and results in poor ride quality.
Conventional wisdom states that installing stiffer springs will make your Mustang ride more harshly. The notion that dramatically increasing the spring rate will destroy ride comfort is akin to getting a "free lunch." However, our Maximum Motorsports coilover conversion increased handling without the usual side effects.
How is this possible? A coilover conversion increases wheel rate and improves ride quality by eliminating friction in the suspension. A '79-'04 Mustang's "modified MacPherson strut" suspension squeezes the spring between the control arm and the frame rail. This was most likely done for packaging and cost reasons, however, this arrangement puts a lot of force on the control arm bushings and ball joint.
Force creates friction, resisting the suspension's movement, and translating more ride harshness to the chassis (see Figure 1). A coilover conversion puts the spring "over" the strut so the spring acts directly through the spindle, removing the spring force from the control arm bushings and ball joint (see Figure 2). Less force on these parts reduces friction, transferring more suspension forces to the spring, and less to the chassis.
Along with matching Maximum Motorsports "Sport" shocks and struts, we installed 400-lb/in front and 650-lb/in rear coilover springs. We set our ride height about 1 1/2-inches lower than stock in the front, and 2-inches lower in the rear. Even with a wheel rate about twice that of the stock springs, we felt virtually no increase in ride harshness!
With the spring over the strut,...
With the spring over the strut, most of the suspension forces bypass the control arm on their way to the spring. The control arm bushings and are relieved of the stress of supporting the car’s weight. The remaining force is due to the strut’s angle (if the strut was completely vertical, there would be no force on the control arm bushings and ball joint). In this example, the result is nearly a 70 percent reduction in friction!
Overall, we were extremely impressed with the ride quality and handling (despite it having the wheel rate of a Grand-Am professional road racing car) after installing the Maximum Motorsports coilover kit. The springs felt perfectly matched the Maximum Motorsports "Sport" dampers, which made the car feel more controlled and "tied down" through turns and over bumps. The steering felt lighter and more accurate, thanks to less ball joint friction (earlier cars that don't have "low friction" ball joints will benefit even more than we did). Due to their continuous development from racing experience and customer feedback, the quality and attention to detail in the Maximum Motorsports parts and installation instructions was impressive. Let's get started!
Modified MacPherson Strut
For an SN-95 Mustang with...
For an SN-95 Mustang with independent rear suspension (IRS), this is what Maximum Motorsports (MM) offers to convert it to coil-overs and adjust bumpsteer. Maximum Mo- torsports recommended for 400-lb/in front and 650-lb/in rear springs and matching MM "Sport" shocks and struts.
A conventional MacPherson strut uses coil spring around a telescopic damper (strut). The '79-'04 Mustang uses a "modified MacPherson strut" arrangement, where the spring is relocated to between the control arm and the chassis. This arrangement allows the wider tires and a lower overall height at a lower cost compared to a conventional MacPherson strut.
When a coil spring is installed around a telescopic damper, it's referred to as a "coilover." A conventional MacPherson strut is a coilover.
A conventional strut consists of a body housing the damper piston and fluid, with the shaft extending out the top of the body. The shaft carries the suspension's bending forces and damper forces simultaneously.
An "inverted strut" is a conventional strut that's inverted, with the shaft encased in another tube and a guide bushing at the top. It's stronger because the suspension's bending forces when cornering are carried by the large damper and mounting body bushings, leaving the thinner damper shaft and smaller bushings to carry the damping forces. This minimizes friction and alignment changes.
1 We started by removing...
1 We started by removing the brake caliper, rotor, ABS sensor, and swaybar end-link. A tie-rod removal tool borrowed from a local auto parts store made removing the tire rod a snap.
Wheel rate is the effective suspension spring rate as measured at the wheel. Depending upon suspension arrangement and geometry, the wheel rate is usually a fraction of the spring rate. A heavier wheel/tire package increases wheel rate.
A stock '79-'04 Mustang's front wheel rate is 1/4 of the spring rate. A Mustang Cobra independent rear suspension (IRS) has a wheel rate that's 1/3 of the spring rate. For example, a stock '03 Mustang Cobra has 600-lb/in springs front and rear.
- Front wheel rate = 600 lb/in x 1/4 = 150 lb/in
- Rear wheel rate = 600 lb/in x 1/3 = 200 lb/in
Front coilovers have a wheel rate of 9⁄10 the spring rate. Rear IRS coilovers have a wheel rate that’s 1⁄2 the spring rate. For example, an ’03 Mustang Cobra with coilovers has 400-lb/in front springs and 650-lb/in rear springs.
- Front wheel rate = 400 lb/in x 9⁄10 = 360 lb/in
- Rrear wheel rate = 650 lb/in x 1⁄2 = 325 lb/in.
2 We supported the lower...
2 We supported the lower control arm with a floor jack and used a breaker bar to loosen the strut mounting bolts. After unscrewing the strut top nut, we removed the OEM strut.
3 With the strut removed,...
3 With the strut removed, we slowly lowered the control arm to unload the spring. We've never had luck using a spring compressor to remove front Mustang springs so we just used a pry bar to pop the inner edge of the spring from the control arm, but WATCH OUT! The springs you're removing will determine how much preload they'll still have, and thus how much they jump out of the control arm pocket. Soft V-6 or GT springs will pop out more than most aftermarket lowering springs, which practically fall out by themselves.
4 Note how, when compared...
4 Note how, when compared to the OEM strut, the Maximum Motorsports strut ears are heavily reinforced to keep the strut ears from twisting under heavy braking forces.
5 Here's an "exploded view"...
5 Here's an "exploded view" of the parts to assemble the front coilover. Like the OEM Cobra's Bilstein struts, the Maximum Motorsports strut is an "inverted" design. This makes the strut stiffer than a conven- tional strut because large guide bushings are used to give the strut very high bend- ing stiffness. This minimizes friction and alignment changes under hard cornering.
6 We began assembling the...
6 We began assembling the coil-over strut by installing the included clamp collar, threaded sleeve, lower spring perch, dust boot, and spring.
7 A nice touch is that Maximum...
7 A nice touch is that Maximum Motorsports uses two O-rings to keep dirt out of the upper spring perch thrust bearing. One is sandwiched between the upper spring perch and the dust boot, and the other goes in the groove on top of the upper spring perch.
8 Before we installed the...
8 Before we installed the coilover strut, we compared weights. The coilover assembly saved about five pounds over the stock setup.
9 With the coil-over assembled,...
9 With the coil-over assembled, we installed it in the car.
10 On the driver's side,...
10 On the driver's side, there's a flange that could interfere with the coilover spring. To make flattening the flange easier, Maximum Motorsports included a tool that attaches to a 3/8-inch socket. After working the tool along the flange, we had plenty of clearance between the spring and the chassis.
11 The bottom hole of the...
11 The bottom hole of the MM Bilstein struts is oversize to provide a greater range of camber adjustment. To avoid re-setting camber each time the strut is removed, MM recommended we install the strut at either the maximum negative or maximum positive position. We chose the maximum positive position for our street car.
12 For the sway bar to be...
12 For the sway bar to be effective, its ends need to be level. If the suspension is lowered, then shorter end links are required. Maximum Motorsports offers end links in various lengths.
13 We finished the front...
13 We finished the front installation by tightening the strut mounting nuts to 155 ft-lb and putting everything else back together.
14 With the front finished,...
14 With the front finished, we moved to the back. To remove the rear spring, we used an internal spring compressor that we borrowed from a local auto parts store.
15 We removed the trunk trim...
15 We removed the trunk trim panels and the shock top hardware. With the control arm supported by a floor jack, we then removed the lower shock mounting bolt and the OEM shock.
16 This "exploded view" shows...
16 This "exploded view" shows the parts included with the Maximum Motorsports rear coilover kit.
17 We began the rear coilover...
17 We began the rear coilover assembly by threading the lower spring perch onto the threaded sleeve and sliding the sleeve over the Maximum Motorsports Sport shock until it was above the Spirolox groove. To make it easier to install the Spirolock over the shock body, MM includes some shim stock that helps expand the Spirolock so it slides over the shock body and into position.
18 Next, we greased up the...
18 Next, we greased up the shock eyelet, lower shock mount bushings, and crush sleeve with the supplied grease. A coilover kit heavily loads these bushings, so Maximum Motorsports specifies a high-grade material that's four times the cost of standard
19 Next, we installed the...
19 Next, we installed the spring, upper spring perch, and snap ring.
20 Maximum Motorsports includes...
20 Maximum Motorsports includes this trick upper pivot bearing that's designed to maximize bump travel and allow the shock to pivot freely and reduce stress on the shock shaft. We lubricated the Delrin ball and hard-anodized aluminum socket with the supplied grease and installed the assembly onto the shock shaft. The grease is really nasty, sticky stuff, so we wore disposable gloves.
21 With the sub-assembly...
21 With the sub-assembly complete, we fitted the coil-over to the car and fitted the upper shock bushing and hardware.
22 To compensate for the...
22 To compensate for the gap between the bushing sleeve and the bushing, we added the supplied 1/2-inch thrust washer and torqued the lower shock bolt it to 98 ft-lb.
23a The instructions warned...
23a The instructions warned us of interference between the spring and the inner fender, which we encountered.
23b Some quick work with...
23b Some quick work with a pair of vice-grips created the clearance we needed.
24 After setting the ride...
24 After setting the ride height, we secured the lower spring perch's location with the nylon-tipped set screw. Here's the finished installation before we installed the wheel and lowered the car to the ground.
Here's a shot of the car with the stock ride height, and the new stance after lowering 1-1/2-inch in front and 2-inch in back.