The 1999 Mustang boasts major refinements to its chassis, suspension, steering, and braking. The first-ever traction-control system for the Mustang is standard equipment on all models, and shares many electronic and mechanical components with the ABS. It also uses a power-train control module to limit engine torque on detection of a spinning wheel. When the ABS sensors notice excess drive-wheel spin, the power-train control reduces slippage with a combination of actions to limit torque. This reduces fuel flow through the injectors, retarding the spark timing, and cuts off spark and fuel to one or more cylinders while applying the brakes at one or both of the drive wheels.
The system works at all speeds and controls either driven wheel independently or both together. It allows optimum use of available traction while accelerating or cornering, and helps with steering control and stability if the car accelerates at mid-corner. It also has a power start feature integrated into the traction control. This allows more wheel spin compared to the normal operating strategy if the driver is attempting full acceleration on a slippery surface. Drivers control the system via a console-mounted on/off switch.
Chassis changes increase the driveline tunnel height by 1.5 in. at the rear. This allows an increase of about an inch of travel in the rear suspension before it bottoms out on bumps. Accordingly, Mustang suspension engineers specified new rear springs and retuned the springs, shocks, and stabilizer bar. This gives a smoother ride with fewer abrupt jolts. Also, the rear track is 1.4-in. wider on both the V6 and GT models for better handling. It also improves the appearance of the tire-to-fender relationship.
New springs and revised front suspension tuning gives a less harsh ride. However, the biggest change up front is in the steering. The stop position for the rack-and-pinion gear module has been changed. Ditto for the lower control arm and stabilizer bar mount. These revisions let the wheels turn farther, reducing the turning radius and making the car more maneuverable. The V6 model’s turning circle is 37 in. smaller, and the GT’s drops 31 in.
On Mustang convertibles, full-box section extensions join the front and rear chassis rails. The braces bolt to the floor pan to boost chassis rigidity, reducing flexing during acceleration, braking, and cornering.
Both the V6 and V8 power plants produce more horsepower and torque. The 3.8-liter V6 gains 40 hp and 5 lb-ft of torque. It carries a 190-hp rating at
5,250 rpm, with 220 lb-ft of torque at 2,750 rpm. The power increase comes from better engine breathing via a new intake manifold with two runners per cylinder, and flow improvements in the cylinder head. A new piston coating that reduces friction also helps boost power. A balance shaft in the V6 helps cut vibrations. Stiffening ribs on the front and rear faces of the block help minimize them as well.
The V8 boasts a 35-hp increase. It carries a 260-hp rating at 5,250 rpm. Torque is up 10 lb-ft to 302 at 4,000 rpm. Contributing to the power gain are camshafts with higher lift and longer duration, bigger valves, and intake-manifold runners that are straighter than previous versions. Also, the combustion chambers are optimized to better mix the air-fuel charge. Fuel burns more completely, optimizing power and fuel economy, and reducing emissions. Larger 3-in.-diameter dual tailpipes on the GT handle the exhaust. The ’99 V8 incorporates an ignition coil on each spark plug, providing a high-energy spark for better burn properties. Aluminum upper main, upper thrust, and rod bearings improve durability.
There are closer mesh tolerances in the slip yoke, where the steering column can collapse in a crash. This reduces free-play in the steering. The power-steering system provides more boost, giving a more direct road feel and better steering linearity, especially at highway speeds.
The front brakes now sport twin-piston aluminum calipers. The aluminum parts reduce unsprung weight and, combined with a new brake pad material, make for smoother braking. Also, an increase in the master cylinder size and a bigger brake pedal ratio for the GT reduce pedal effort and make it easier to adjust pressure on the brakes. The master cylinder size increase for both the V6 and V8 results in longer stroke due to a center valve in the traction control units.
Sound-deadening materials quiet the interior. The floor pan includes sealing around the attachment points for the rear shock towers, rocker edges, and seat attachment areas. Expanding foam insulation in the ends of the rocker panels helps block noise paths into the A and C-pillars.
New body styling includes slim, wraparound headlamps, stepped, tribar taillamps, and a rear deck of sheet-molded compound, reducing weight and eliminating corrosion. All 1999 Mustangs have a 35th anniversary version of the tricolor bar emblem on the sides of their front fender.