Overview

Part of the effort to reduce weight and improve handling, the 2004 TL incorporates an all aluminum-alloy subframe that holds the engine, transmission and lower suspension links.

At about 23 lbs (36 percent) lighter than before, the subframe is also more rigid and reduces NVH into the car.

Acura has paid attention to the engine and transmission mounts to make the car drive and idle smoothly. There are a pair of special fluid-filled Electronic Control Mounts which is connected to the hydroformed aluminum-alloy subframe. There is also a side mount that controls side to side motion. The 6MT adds a damper that reduces engine-rocking when during hard shifts or acceleration.

Front Suspension

• The front suspension is a classic Honda upper and lower arm with coil-over shocks.
• The upper arm is shorter in order to increase negative camber while cornering.
• The 5AT gets beefy 25.4mm hollow front anti-sway bar and a 17mm solid rear bar. The sportier 6MT gets an even larger 27.2mm hollow front bar and 20mm solid rear bar.
• There is a hollow steel bar across the shock towers to increase chassis solidity.

Rear Suspension

• The rear suspension is a 5-link independent system with struts, coil springs and anti-squat and anti-lift geometry, and is mounted to a steel subframe to reduce NVH.
• The rear suspension geometry adds "toe-in" when the suspension is compressed, improving handling stability over bumps and during hard cornering and braking.
• A stabilizer bar further improves handling by limiting body roll, while a special "pillow joint" for the lateral links improves camber rigidity.
• Rubber shims added to the leading and trailing arm bushings improve ride comfort.

Steering

• The TL uses an engine-driven variable output pump (torque-sensing) to vary the amount of steering assist to ensure a medium effort at slow speeds and linear/firm feel at high speeds.
• Hydraulic steering dampers built into the system further improve stability during cornering and at high speeds. A one-way kickback valve decreases kickback in the steering wheel that can be caused by road irregularities. The hydraulic valve closes when it senses road irregularities, impeding disturbances to the steering wheel.
• Increasing the stiffness of the steering gearbox mounting and the rear sub frame also maximizes steering linearity.

Brakes

• The 2004 TL has 4-wheel disc brakes with Electronic Brake force Distribution (EBD), Brake Assist, an Anti-lock braking system (ABS) and 4-channel Vehicle Stability Assist (VSA) including Traction control as standard equipment.
• On the 5AT, the front brakes are ventilated cast-iron discs with single-piston calipers.
• On the 6MT, Brembo rotors and aluminum-alloy front brake calipers are standard. The calipers have four pistons each, and more aggressive pad material. They are also 30 percent lighter than the standard calipers, saving 4.3 pounds per wheel.
• Cooling air flows to the brakes through the front fender air duct ahead of the front wheels which reduces the brake temperature by 84F in high-demand fade tests.
• The rear brakes are solid discs, gripped by single piston calipers.
• A single 10-inch vacuum booster is used to reduce weight, increase stiffness and deliver more direct braking feel.
• In both the automatic and manual transmission models, a hand parking brake is used instead of a foot brake.
• Stopping distances from 60 mph have improved considerably from the previous TL Type-S. In internal testing the 2004 TL with all-season tires out-brakes the Lexus ES 300, and when equipped with high-performance tires the 2004 TL out-brakes the 2003 BMW 530i (also with high-performance tires).

Electronic Brake force Distribution

A new feature for TL is Electronic Brake force Distribution, which continuously and automatically adjusts the pressure distribution between the front and rear brakes depending on how the vehicle is loaded.

Brake Assist

The concept of brake assist was developed as a result of many people not braking with full force during an emergency situation. For example, the person may be small statured and is unable to physically apply the necessary pressure on the brake pedal. The system on the TL uses a microprocessor to learn the normal pressure applied by the driver. During an emergency or sudden hard braking situation, the system will detect that the brake pedal application speed and pressure thresholds have been exceeded. The system will then apply full ABS activation.

Like most brake assist systems, full braking is only used in emergency situations. Brake Assist will deactivate when pressure is slightly released from the pedal. The TL makes do with a 3 channel ABS where the front wheels are independently modulated, while the rear is done as a pair.