Cars are incredibly complex machines, with (on average) around 30,000 components carefully assembled and wrapped in a pretty body, all designed to give you years of trouble-free motoring. Of course, some components wear out, either by design, or by fault, but for those parts that are designed to wear, most of them are replaceable.
Along with your brakes, clutches (in a manual transmission) are one of the most common wear parts, and replacing them can be difficult, or costly, but how do you know when your clutch needs replacing?
First up, we should understand the job of the clutch in a transmission.
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Drivetrain and Clutch
The clutch consists of three main parts; a friction or drive plate, a pressure plate (or clutch cover) and a release bearing. Discounting the release bearing for the moment, the actual components that ‘drive’ the transmission or gearbox are the drive plate and pressure plate.
The clutch itself is the link between the engine and the gearbox, literally sitting between the two – attached to the engine’s flywheel and the gearbox’ input shaft. As the engine turns, the job of the clutch is to transfer the engine power through to the gearbox, which in turn rotates the driveshafts and wheels, more commonly known as the drivetrain. Over a period of time, the friction plate wears, leading to a condition called ‘clutch slip’.
Clutch Slipping Symptoms
Identifying a slipping clutch is easily done – it usually starts happening when the engine and drivetrain are under most load – 4th or 5th gear, with the accelerator pushed down, trying to build speed up in the higher gears.
You’ll notice that the engine revs will rise quickly, with no noticeable surge in speed – the revs won’t match the acceleration, this is usually a slipping clutch (unless of course you’re driving a 600+ horsepower monster and you’ve broken traction at the wheels).
Backing off the power and gently easing your foot down again is the kindest way of stopping the slipping clutch; if you carry on and let it slip, it will overheat the clutch plate, which will exacerbate the problem. The problem of clutch slip is two-fold – the drive plate wears, leading to being less able to cope with the engine/drivetrain load, and as the drive plate heats up, it loses some of the ability (temporarily) to cope with the demand.
So when you do reach the point of clutch slip, and overheating, the clutch will just give up and stop transferring the power.
Hydraulic VS Cable
Older cars generally use a wire cable to operate the clutch, whereas newer cars use a hydraulic system, that actuates a ‘slave’ cylinder, which in turn operates the arm and engages the release bearing. With the older mechanisms, it’s entirely possible that the clutch cable needs some adjustment – even though it stretches as it wears, sometimes the mechanism moves, pulling the cable taught, which leads to a clutch slipping situation.
In this case, you’ll get all the signs of clutch slip, only it’s easily (and cheaply) resolved – a minor adjustment rather than splitting the gearbox/engine.
Of course, unless you own a vintage or classic car, it’s unlikely that you’ll come across this problem, but on the off chance, it’s worth knowing.
Truthfully, an article on how to replace a clutch is an impossible thing; despite being similar, cars and their drivetrains can all be different, but there are some basics that could help you understand the process before thinking of attempting it yourself.
Manufacturer VS Aftermarket
If you’re looking to replace your clutch, the first decision to be made is whether to buy a genuine manufacturer part, or aftermarket. If your car is still under the warranty period, then anything other than genuine parts may invalidate your warranty, even if it’s completely unrelated.
Aftermarket parts are generally much cheaper than genuine, and for some, this equates to cheaper quality, but this isn’t necessarily the case. It has been known for a manufacturer to supply components to both car manufacturer and aftermarket, meaning the product is identical. Also, despite being cheaper, this is usually just the mark-up that’s added for the genuine part, this can be as much as 70%.
Our recommendation would be to choose a good quality aftermarket assembly.
Despite it often just being the clutch drive plate worn, we’d always replace all the relevant components such as the pressure plate and release bearing. The parts do wear at different rates, but the simple fact is that the parts will have worn, and given that splitting the engine & gearbox is a time-consuming (read expensive) process, you’re better off replacing them all at the same time.
Wouldn’t you just kick yourself if you replaced the clutch drive plate, put everything back together and then a month later need to do the same again to replace the release bearing?
You should also consider why the clutch has worn; has the car done an expected mileage? Or is there a problem that has caused the clutch to wear prematurely? A good indicator of potential problems or abuse is the state of the flywheel to which the clutch is attached to – blue spots on the surface indicate an excessive amount of heat, this could be due to the clutch having an exceptionally hard life or a potential problem.
If you’ve covered an expected amount of trouble free mileage from you clutch, the chances are that doing a straight replacement is all that you need, but a visual check for problems won’t cost you anything.
If you’ve decided to take the choice to replace the clutch yourself, you probably already have most of the tools you need – socket set, spanners, screwdrivers and the like, but you’ll also need a clutch alignment tool – so that the input shaft from the gearbox will fit straight through, nestling into a bush or bearing in the back of the crankshaft.
Some people are tempted to make their own alignment tool, believing that if it’s somewhere near right, they’ll be ok, but trust us on this … lifting a gearbox above your head and trying to align it is not the time to find out whether your home made tool was accurate enough.
Some vehicles allow for an easy clutch replacement – being able to split the gearbox and engine enough to slide the clutch assembly out (with some fiddling), whereas others require the removal of the gearbox completely. It’s worth trying to understand where your car would fit in that process – believing that you’ve done everything necessary, and then spending and hour trying to lever out your clutch assembly when the manufacturer has made it so you can’t is not a productive way to spend your time!
There are plenty of resources available to research your car, from owner’s groups to online manuals, all can be a wealth of information.
Replacing your clutch is a big job, perhaps one of the biggest that could be done at home, so don’t underestimate the complexity or nature of the work. If you don’t have access to a car lift, or ramp, the bare minimum you’ll need is axle stands and a good jack.
If you have to remove the gearbox completely, you’ll need the vehicle high enough on the ground to lower the gearbox from underneath the car, and be wary of the gearbox oil or fluid leaking out.