By John Carollo
Photos by John Carollo and Hays Clutches, action photo by Tim Marshall
11/15/07
Think of the clutch as a bridge between your engine and transmission. If it’s not strong or effective enough to let that power across, you’re not going to get: the value of the money you spent on the engine’s power, effective power to the transmission, and to kick any butt at the track or anywhere else.
If you put huge skid marks on your credit card buying a killer motor or if your current motor is an anemic wheezer, THAT will factor in choosing a clutch. So will your tranny and what rear end gear you’re running.
So how do you know what clutch to use? Well, first you need to know just how a clutch works. We already know that a clutch is designed to connect an engine that is already turning rpm to a transmission shaft that is not. Even in the case of a gear change, the two are turning at dissimilar rpm. The basic idea is to have two different rpm speeds mesh smoothly and efficiently without loss of power or momentum.
Engage a clutch and it does two things: rotate the transmission shaft as it receives rpm from the motor (initial transfer of power) and put a load on the motor (recovery rate). These factors decided by what you’ve got on either end of that clutch; the motor and the tranny. And don’t forget your rear end gears. If you’re running a tall (numerically lower ratio) gear, that has to be considered. Your particular driving style is also a factor. The best thing we can tell you about driving style and your clutch is to be honest. If you lug around town barely moving or if you think you’re Dale Jr. at Daytona, your driving style matters.
It may sound like a gratuitous trick but we’ve learned one of the best ways to find out what clutch is best for you is to take advantage of manufacturer help lines and customer service people. They have the knowledge. The materials and methods used in clutches now are miles from the long-gone asbestos days. Here’s another tip for clutch shopping. You’ll get your best results by staying with one manufacturer. A conglomeration of parts from various brands could end up with them working against each other and even wearing out faster.
Just what components are considered part of a clutch assembly? The important pieces are the clutch disc, pressure plate and throwout bearing. Ideally, keeping those parts together in design, selection and buying sequences are the keys to building a good system.
And if you’re wheels are a truck, you’ve got your own set of clutch notes to check. Like cars, the first is use. If you’re towing or hauling with your truck, you need to know that truck clutches are different from car clutches. Traditionally, aftermarket truck clutches are bigger and stronger than car versions and have as much as 10–25 percent more grip and usually a higher clamping load than OEM units. That’s because aftermarket pieces use material with a better coefficient of friction and/or a more aggressive friction material. If you use that grip wrong, it could put undue stress on your transmission and rear end. And if you don’t have enough grip in your clutch, your motor will operate at less efficiency.
Flywheel ring-gear size determines clutch size, fitting within the bolt circle of the crank and matching the pressure plate.