Transmissions

The Clutch

If the engine power is to be increased by 15-20% or more then a heavy duty road spec clutch should seriously be considered. This type of clutch is a direct replacement so no modifications are required. Because it has an increased pressure rating the effort required to depress the clutch pedal will also increase. For serious road/rally applications the conventional organic material clutch plate can be substituted for a cerametallic paddle plate. The durability and grip of a cerametallic plate far exceeds the conventional plate but some degree of clutch feel will be sacrificed, together with a level of clutch vibration, when engaging. Lastly, for competition use only, single or multi-plate race clutches are available for a large range of applications. Special steel flywheels are required for all race clutches.

Modern day clutch disc material is typically 50% harder wearing than the now superseded asbestos material, making clutch replacement less frequent. One disadvantage of this is that it tends to accelerate wear to the flywheel and clutch cover contact surfaces. When replacing a clutch, the condition of both surfaces is highly important. A new hard wearing clutch disc will not bed into worn and uneven flywheel and clutch cover surfaces and failure of the clutch is certain. If in doubt, always reface the flywheel and change the clutch cover with the clutch disc.

When fitting the engine to the gearbox, never allow the gearbox to ‘hang’ on the clutch. Both gearbox and engine should be supported. As soon as the engine and gearbox have been mated together, they should be bolted together immediately. This will prevent the possibility of distorting the clutch disc, causing it to run out of true. • Check for any oil leaks before renewing a clutch. Oil contamination from a leaking rear crank seal or front gearbox seal will render a clutch useless.

Where a clutch cover has been supplied with grease/rust preservative on the pressure plate surface, make sure this has been thoroughly removed prior to fitting.

FWD Escorts - check the top bush on the release bearing shaft. These frequently wear and will cause clutch judder.

Never overlook propshaft bushes. When worn, these often cause vibrations.

Always check the spigot bearing which supports the gearbox input shaft. Again, this will cause clutch judder and in extreme cases can result in failure of the clutch plate and damage the gearbox.

The Gearbox

More engine power = more torque = higher loadings on gear teeth and bearings + take-up shock from competition clutches = broken gearbox! Most standard gearboxes will cope with a moderate increase in abuse but there is a limit. If you have an old 4 speed set up, the chances are there is a stronger 5 speed box available which, with the right bellhousing and mountings, will be an ideal replacement. For faster more positive gear changing, quick shift levers and kits are available for many of the more popular gearbox types. Uprated internals together with alternative gear ratio kits are available for a selected range of O.E. and special equipment gearboxes.

The Final Drive

For serious competition use it may be necessary to change the differential ratios to suit circuit variations. Special attention should be paid to drive shafts which are a specific weakness on most cars. And lastly, to achieve maximum traction from the driving wheels a limited slip differential unit (LSD) is a must for all competition cars.