We lift the curtain on the black art of clutches
With so many people chasing big power and towing big loads with their 4WDs it’s not surprising to see weak points starting to pop up all throughout modern drivelines. From axle studs to free wheeling hubs we’ve just about seen them all, but one modification that’s starting to become more and more common is clutch upgrades. Just a few years ago a clutch upgrade was something you’d rarely see outside of an engine converted 4WD or people pushing their rigs to the extreme towing loads bordering on illegal. The poor bugger stomping on the clutch pedal would usually end up with a left leg that’d look right at home on an Olympic weight lifter just from the excessive pedal pressure required to engage and disengage the clutch. Nowadays, clutch upgrades are a little more routine, and a whole lot better in the results department. Combine that with the increasing demands we’re putting on our 4WDs and it’s pretty obvious why they’re becoming such a popular upgrade. But how exactly do they work, what makes the stock unit not up to the task, and when should you look for an upgrade? Well you’ve come to the right place to find out.
HOW DOES A CLUTCH WORK
Before we can get too caught up on the ins and outs of upgrading clutches it’s important to know exactly how they work. From the driver’s seat it’s just a push on a pedal and you’re off and running, but the actual mechanics are a little more involved. To stop your engine stalling as soon as you stop and facilitate smooth gear shifts you need a way to physically disconnect the engine from the rest of your driveline, this is where clutches come in. At the back of your engine (if you have a manual gearbox) you’ll find a large metal disc called a flywheel.
Bolted to that are the two major components that make up a clutch; the clutch plate attached to the gearbox, and the pressure plate attached to the engine. When you take your foot off the clutch pedal the pressure plate pushes the clutch plate into the flywheel, from there the high friction material on the clutch plate bites into the flywheel until the two are locked together and drive is sent through to the gearbox. Think of it a little like a reverse brake setup. With your brakes when you press the pedal your brake pads are pushed into a disc until eventually the speeds match and your 4WD stops. With a clutch the clutch plate is pushed into the flywheel until the speeds match and you take off.
WHAT KILLS THEM?
Just like brake pads wear down over time and should be replaced, your clutch is a consumable item and needs to be looked at the same way. By their very nature they’re constantly losing material every time they work, so expecting one to last forever is a recipe for disaster. That said, there are a few things that’ll kill off a clutch quicker than expected. Most issues will result around the clutch plate material wearing away or physically not being able to hold on to the flywheel anymore, this is commonly known as clutch slip.
Premature wear of the friction material can be caused in a number of ways. In street driven vehicles it’s generally hard launches, riding the clutch, and resting your foot on the clutch pedal that will wear away the friction material. In a 4WD it’s often caused by putting more load into the system than the clutch can hold, breaking its grip on the flywheel. This can be caused by towing heavy loads, power upgrades, or even fitting larger tyres.
Another often overlooked aspect of clutch failure is the pressure plate. While the clutch plate itself may have enough friction to hold onto the flywheel, if the pressure plate can’t hold it against the flywheel clutch slip will still occur. No matter what the point of failure is the result is a 4WD that’s not able to get power to the ground.
DO YOU NEED AN UPGRADED UNIT?
For some people this is a simple answer, for others it’s a little more complicated. If you have a late model 70 Series LandCruiser or HiLux you need a clutch upgrade, it’s as simple as that. The standard units are so weak Toyota have knocked back warranty claims on slipping clutches because of simple power upgrades like an exhaust system. If an extra 10hp will finish them off what chance does it have of holding up to towing a camper trailer, caravan, or even serious off-road work?
For anyone else there’s a few questions you need to ask yourself. Your clutch was designed to handle a standard configuration 4WD doing standard work. If you’ve fitted accessories such as power upgrades or larger tyres you’re probably asking more of your clutch than it was designed too. Likewise, towing heavy loads or travelling in hilly or sandy terrain can both easily overcome a standard clutch. If you’ve found your 4WD doesn’t pull as hard as it used to it may be a slipping clutch and a prime candidate for an upgraded replacement.
WHAT TO LOOK FOR
It’s easy when heading down the upgrade path to go for the biggest baddest option you can find, but it’s not always the best solution. A clutch that bites hard is easy to make, but the result will be an on or off type of situation which will be an absolute pig to drive and doesn’t necessarily mean it’ll last any longer than stock. A quality clutch upgrade needs to be looked at like a whole system, and is very rarely a one size fits all package. For most 4WDs we’ll offer one of a few options from Exedy’s Safari range or NPC Performance Clutches. Depending on the customer’s needs we’ll tailor a package that’ll provide up to three times the stock clamping force to deal with the loads of towing, power upgrades, and increase tyre diameter and vehicle weight. We can balance that with custom flywheels and pressure plates to maintain a stock or better pedal feel. Friction surfaces are also upgraded with premium materials to ensure the new clutch doesn’t just feel and perform far better than a stock unit ever could, but will last longer as well. Your 4WD can only perform as good as its weakest link. If your clutch is shuddering, slipping, or just too hard to control you’ll spend your time fighting your 4WD, rather than enjoying it.