While flying over the Pacific Ocean returning home from my brief vacation in Hawaii, I was flipping through a Japanese high-performance car magazine to kill time.
I scanned the entire magazine for photos, like most enthusiasts who are rather illiterate when it comes to Kanji. My fourth time around looking through the magazine (it was a long flight), I was surprised to see how many high-performance clutches were on the market for high-powered import cars. In just one magazine, I was able to count more than 50 different clutch manufacturers with several different clutch combinations for the exact same vehicle.
Although having more than one choice is a good thing, having too many can become a burden. This month's "Tech Scene" will help you choose the right clutch for your high-performance ride.
The first question you should ask yourself is, why do I need to replace the clutch? Is the clutch slipping? If it isn't, don't replace it. Replacing a clutch is not cheap. Parts and labor combined can run anywhere from $800 to $1,000. If it is slipping, why? Is it due to normal wear and tear? If not, is there oil in the bell housing? If there is, the vehicle could have a worn rear main seal or transmission seal. If the situation is not fixed, a new clutch will likely fail as well. Replacing the rear main seal along with the clutch install is highly recommended if it hasn't been replaced before. The part usually costs about $20 and most mechanic shops won't charge you much to install it with the transmission off. Replacing the $20 seal would prevent you from paying for another clutch and installation.
The next question you should ask yourself is, what type of driving am I going to be doing most: street, street/strip or strip?
If you are only planning to street drive your lightly modified vehicle, you probably don't want to purchase a full race clutch; the same goes for racing the vehicle. There is no such thing as "one size fits all" when it comes to clutches. Knowing the type of driving you will be doing most will help you dramatically narrow the choices. One of the mistakes of purchasing a clutch is using a four-puck unsprung strip disc on a street-oriented vehicle. Stick with a sprung-hub set-up, even if your vehicle calls for a four- or six-puck design. The sprung center disc will reduce the amount of chatter from the clutch and decrease the chances of other driveline parts failing.
Another mistake is to never try to use a dual- or triple-disc set-up on the street. Unless it's a full-race vehicle, there is no need for such a set-up. Neck-snapping shifts might be cool to you and your friends, but after a week of stop-and-go traffic, you can kiss your transmission and axles goodbye. Before purchasing the clutch from your local speed shop, try calling the manufacturer of the unit. Make sure the clutch you are purchasing suits your driving needs.
The third important point is to never skimp on wear-and-tear parts. Always replace the throwout bearing and pilot bearing (when applicable) with every clutch exchange. Some high-performance clutch packages come complete with brand-new throwout and pilot bearings. Although the combos are oftentimes a bit more expensive, the overall price is usually still cheaper than purchasing the individual parts, one by one.
Many enthusiasts often make a mistake when it comes to properly resurfacing the flywheel. Without the proper flat contact surface on the flywheel, clutch performance can be hindered. All flywheels are likely to be scored and warped from heat over time, due to normal usage. Also, when it comes time to do so, make sure a qualified technician with the proper equipment resurfaces the flywheel. A mere scoring of the contact patch with sandpaper or a hand-held grinder/sander is not recommended. Always refer to a factory service manual for flywheel resurfacing specifications (flat, step, etc.; see figure A) on your vehicle. If a flywheel is not resurfaced to the proper specifications, clamping pressure from the pressure plate can be compromised.
The greatest mistake is not following the directions and not performing the proper break-in procedures.
A brand-new clutch and resurfaced flywheel requires a break-in period of about 500 to 750 miles. The break-in procedure ensures a proper mating surface between the flywheel, clutch disc and pressure plate. If a brand-new unit is driven hard from the get-go without the proper break-in, it can suffer scoring on the clutch assembly and flywheel, which can accelerate its wear or cause catastrophic failure.
For more information on choosing the right clutch, we recommend reading "The Clutch Bible" from Centerforce.
Having a clutch installed can definitely challenge the wallet; we hope this month's "Tech Scene" will keep you from breaking the bank.