The clutch is one of the hardest-working components in a car and withstands enormous speed differentials, pressure and heat.
It’s also one of those components that you don’t really think about until it stops working.
A good clutch should enable smooth and silent gearchanges while a bad clutch – be it burnt out, distorted or just worn – will quickly make you fall out of love with your classic car.
The clutch consists of three main parts: the clutch plate, which is made of friction material and transfers drive from the flywheel to the gearbox input shaft; the pressure plate, which uses springs to ‘push’ the clutch plate against the flywheel; and the release bearing, which moves the pressure plate to release the clutch plate – and disengage the clutch – when the pedal is pressed.
Given that changing a clutch involves removing the gearbox and often the engine, too, it’s cost-effective to replace all three items, none of which typically wears in isolation.
Remember that older clutches contain asbestos, so wear appropriate protective gear, and reassemble using new nylock nuts or shake-proof washers where appropriate.
STEP 1: IDENTIFY THE PROBLEM
It’s crucial that you know what’s wrong before diving in, especially if you have to pull the engine out.
Is it grating when you change gear or slipping when you accelerate? The former could just mean it needs adjusting or bleeding to remove air from the system. Vibration at speed could be an unbalanced propshaft.
STEP 2: DISCONNECT SLAVE
You’ll need to either remove the slave cylinder from the bellhousing or disconnect the hydraulic feed if you’re leaving it in situ.
To remove it, first take out the clevis pin that attaches the slave rod to the clutch fork. Before undoing the feed pipe, clamp the flexi-hose to avoid emptying the master cylinder.
STEP 3: REMOVE GEARBOX
Gearbox removal usually involves unbolting the starter motor, prop, speedo drive and any crossmember or chassis-based gearbox mounts.
Be prepared to take the weight of the unit when it comes free of the engine and handle it with care: a lot of cars have an aluminium bellhousing, which can be fragile.
STEP 4: EXAMINE ALL PARTS
The clutch plate is grooved to dissipate heat and so you can gauge wear. If it’s smooth, it’s worn out. The pressure plate should be smooth and crack-free, and its springs a tight fit.
If your classic car has a roller release bearing, spin it and listen for any rumbles. Inspect the clutch fork and flywheel face for damage, too.
STEP 5: INSTALL CLUTCH AND PLATE
The ‘longer’ side of the spigot drive typically faces the pressure plate, the ‘shorter’ side facing the flywheel.
Check the flywheel and pressure plate for markings: they’re often balanced as a unit. Use an alignment tool to centralise the plate then torque the bolts by hand: a pneumatic drive could strip the threads.
STEP 6: REPLACE BEARING
The two types of release bearing are carbon, with a hard-wearing, low-friction surface that meets the pressure plate, and roller, which lets the bearing face spin.
Most British classics use the former, which wears and should be replaced, but both are usually fixed to the clutch fork with spring clips. Always use new clips.
STEP 7: CHECK AND ASSEMBLE
Check the phosphor-bronze spigot bearing at the back of the crankshaft. It wears and isn’t costly to replace: either ‘hydraulic’ it out with grease and a shaft that matches the internal diameter, or drive it out with a chisel.
Soak the new one in oil then gently drive it in. Double check everything before offering up the gearbox.
STEP 8: BLEED AND ADJUST
Reattach the slave and bleed the system. When you feel the clutch working, set up the free play on the slave rod or master cylinder (or both on some cars) to prevent the release bearing resting on the pressure plate.
Tighten any locknuts and road test. Re-check the free play when the clutch is hot and check for leaks.