Inside the 2005 Mustang: combining a live axle, MacPherson struts, and a Lincoln base to build the 21st century's first pony car

Automotive Design & Production, Nov, 2004 by Christopher A. Sawyer

The Mustang platform shares its roots with the Lincoln LS and laguar S-Type (DEW98), but is far enough removed for Ford personnel to stubbornly refer to it as "unique." Gone is DEW98's expensive aluminum-intensive suspension (unequal length control arms in front and a fully independent multilink rear unit on an isolated subframe). In its place sit far more economical MacPherson front struts with "reverse-L" lower control arms and a three-link solid axle with coil springs. A retrograde step? Perhaps, but understandable given the Mustang's under-$20,000 starting price--about $14,000 less than a base Lincoln LS.

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Ford claims the front suspension's steel lower control arm--which looks more like a high-heeled boot than the letter "L"--is lighter than many comparable cast-aluminum designs. It consists of a pair of C-section pieces welded back-to-back at their perimeter to produce an I-beam cross-section. Most of the forces are carried through the arm's perimeter, which means its center can be thin for maximum lightness. Fore-aft movements feed through a fluid-filled bushing at the toe of the boot-like lower control arm, while sharper side-to-side motions feed into a stiffer bushing located in its heel. The combination permitted tuning for sharper steering response while damping the "patter," "jiggle," and harshness--often amplified by the anti-roll bar--that normally is fed into the steering wheel and cabin on uneven surfaces. MacPherson struts liberated enough engine compartment width to fit Ford's Modular V8 under the hood; the more sophisticated Lincoln LS front suspension design would have required use of Jaguar's narrower, smaller displacement V8. (The 2005 Mustang even has enough engine room to fit the Modular V10, should it see production.)

The solid rear axle--chief engineer Hau Thai-Tang insists Mustang owners demanded a live axle--has vertical coil springs, near-vertical outboard-mounted shock absorbers, a single torque control arm located along the vehicle centerline that attaches to the top of the differential housing, a tubular steel Panhard rod, an anti-roll bar (GT model only), micro-cellular urethane jounce bumpers, and lower control arms that attach to brackets located between the shocks and coil springs. In other words, it's a lot more sophisticated than the inclined shocks and leaf springs of vintage Mustangs, but not as sophisticated--or as expensive--as an independent rear suspension design. Compared to the 2004 Mustang live axle, the new version controls longitudinal and lateral forces separately, which greatly reduces head-toss and axle hop.

A good suspension design is worthless, however, if the chassis holding

the pieces together isn't strong and stable. Stiffness is up significantly, with bending measurements up a whopping 49% and torsional numbers--at 15,500 lb-ft.--a significant 31% higher. The increase comes from a number of factors, including the use of dual-phase steel in the rocker panels, high-strength steel in the integral underbody frame rails, tailor-welded B-pillar blanks, a 33% lighter #2 front crossmember, a substantial cross-car beam at the base of the rear seat pan, and a deformable front structure with octagonal rails that spreads forces through the rockers and driveline tunnel.

POWER TO THE PEOPLE

The standard powertrain mates the Explorer's 4.0-liter SOHC V6 to a Tremec T-5 five-speed manual transmission (the 5R55S five-speed automatic is a $995 option) and a Visteon-supplied slip-in-tube driveshaft. This engine, like the V8, has a Mustang-specific throttle body and intake manifold, and also receives a unique camshaft, tuned-length exhaust manifolds, flywheel, oil pan, enhanced fuel injection system, a new EGR system, and a revised cooling circuit. Output for the 12-valve V6 is 202 hp @ 5,250 rpm, and 235 lb-ft @ 3,500.

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The 4.6-liter V8 borrows its aluminum three-valve head design, variable cam timing, and electronic throttle from the F-150's 5.4-liter V8. The heads, in fact, carry the same part number and camshaft design, differing only in how the ECU regulates the variable valve timing control unit. Cast-iron tuned-length exhaust manifolds package close to the aluminum block to optimize flow, and mate to a 2.5-in. mandrel-bent stainless steel exhaust system with bolt-on mufflers. The standard gearbox is Tremec's T-3650 five-speed manual which, like the optional 5R55S automatic, joins to a two-piece driveshaft in order to reduce driveline "shunt." Power output is 300 hp @ 6,000 rpm, and 315 lb-ft @ 4,500--the first time a mainstream Mustang GT has offered this much power.

MEASURABLY DIFFERENT

Four-channel ABS and traction control are standard on the GT, optional on the base car, though both cars offer standard four-wheel disc brakes. Front rotors for each are vented and 1.2-in. thick, though the GT's front rotors are 12.4-in. in diameter versus the V6 car's 11.5-in. rotors. Both models have 1.7-in. aluminum twin-piston floating calipers up front, and 11.8-in. diameter vented rotors clamped by 1.7-in. single-piston floating iron calipers out back.