We began our journey through the drivetrain last month with an analysis of flywheels; now we move on to the clutch system. The clutch basically engages and disengages the transmission, and thus power from the engine, and allows the driver to idle in neutral and to shift gears. The conventional diaphragm clutch is known as a compressed clutch and consists of two basic components, the clutch cover and disc.
The clutch cover is an outer shell constructed from a steel stamping or casting that contains four main components: the pressure plate, diaphragm spring, pivot ring and drive strap. The pressure plate is a cast piece that provides the pivot point for the diaphragm as well as a friction surface for the clutch disc and mounting surface for the drive straps. The diaphragm is a spring-steel disc that is sandwiched between the outer cover and the pressure plate. The steel pivot ring is attached to the clutch cover, creating the fulcrum point for the diaphragm. Also manufactured from spring steel, the drive straps are used to attach the pressure plate to the clutch cover, allowing the plate to disengage from the clutch disc.
The clutch disc is the most critical component in the system. Between the flywheel and clutch, the transmission input shaft goes into the spines of the clutch disc and slides forward and backward, providing fluid engagement. All clutch discs contain a hub flange and friction material. Depending on the vehicle, the clutch disc may contain torsion springs or idle-stage dampers or a combination of both. The friction material used by most OEM manufacturers is an organic-based material, which provides smooth gear shifts and prolongs the life of the clutch system.
There are many important things to consider when upgrading your vehicle's clutch. The first and foremost factor is driveability. If the pedal is too stiff, driving in heavy traffic will be painfully uncomfortable and could cause your left calf muscle to distend to the point of bodybuilder's envy. The second thing to consider is the type of clutch disc and the material the disc is made from. Aftermarket clutch manufacturers use many different combinations of materials and disc configurations to tailor the assembly to specific uses: drag racing, road racing, daily street use, and so on, so make sure you do your homework. If you buy a race clutch disc made specifically for track use, driving that clutch on the street can cause low-end gear chatter, stalling, and decreased clutch life. For daily street use and mild track use, a full-faced organic compound with a copper weave works perfectly.
Advanced Clutch Technology has developed a three-stage clutch program, with increases in pressure plate clamping force ranging from 20 to 150 percent. An exclusive four-stage diaphragm heat treating process is employed to encompass the release bearing contact area and to reduce wear. Each clutch cover is then computer tested to ensure maximum clutch life, clamp load, and release travel.
Applications: BMW E36/E46 M3, Z3, M Coupe; Mini Cooper S; Lotus Elise; Saab 9-2X; all MkI-MkIV Volkswagen chassis except six-speed, Eurovan, Passat B4/B5
Price: From $357
Clutch Masters begins its re-engineering by increasing the clamping force through a process known as the Hi-Leverage technique. This relocates the fulcrum point closer to the pivot point, resulting in a stock-like pedal feel. Four different stages are available, from mild to extreme.
Applications: Audi A4 B5/B6 1.8T five-speed, S4/A6 2.7T; BMW E36/E46 including M, E39 M5, Z3; Mini Cooper S; Volkswagen MkI-MkIV, Passat B3, B4, B5 1.8T five-speed
Price: From $450
Clutch Masters Industries
Eurospec Sport clutch kits contain two unique clutch cover designs. The first uses a dual diaphragm to increase clamping load, while the second cover is machined from ultra light 6061-T6 alloy allowing for maximum rigidity. Clutch discs are available in ceramic or organic materials backed with high-drag-coefficient steel.
Applications: Audi; Volkswagen
Price: From $750
Owning more than 5000 clutch patents, SACHS/ZF knows clutches. The company's Power Clutch system offers the latest innovations in clutch design. With an average clamping force increase of 21 percent, the clutch provides a comfortable pedal feel as well as smooth power delivery for a balance of track-worthy performance and comfortable daily driveability.
Applications: Audi A4 B5/B6 1.8T 5-spd, TT; BMW; Mini Cooper S; Porsche 911, 944, 968, Boxster; all VW except 2.8L V6
Price: From $795
ZF Trading North America, LLC
SPEC High Clamp Load Pressure Plates are standard with all performance kits and feature clamp loads from 20 to 40 percent higher than OEM. Exclusive 360-degree pivot technology ensures a perfectly even lift and disc clamp. This kit features an integrally molded, carbon-based organic lining that provides fluid engagement and is best for street and limited track usage.
Applications: Alfa Romeo; Audi; BMW; Lamborghini Diablo; Land Rover; Mini; Porsche; Volkswagen
Price: From $409
A common misconception about the Direct Shift Gearbox (DSG) transmission is that it is an automatic containing a torque converter. It is actually a manual transmission with a dual friction-based clutch. The HPA clutch upgrade can support a claimed 470 lb-ft of torque, a significant increase from the factory rating of 258 lb-ft.
Applications: Audi A3, TT; Volkswagen Jetta GLI, GTI, Eos
HPA Motorsports Inc.