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Although automatic transmission is more-or-less the norm today, there are still a great many vehicles with single friction-plate clutches. These, unlike auto boxes, are relatively easy to service and repair, albeit a little awkward to access.
If you decide to have a clutch fitted professionally, my advice is to choose your repairer carefully. Cheapest is often not a wise option. Unscrupulous workshops might omit to renew the release bearing or re-use pressure plates that have been machined irrespective of heat cracks.
Also, when a flywheel is reground, the cover assembly mounting flange must be ground by the same amount and often this is not done. Slapdash mechanics or unskilled amateurs may do more harm than good. Damaged splines due to force-fitting the gearbox, release fork linkages with excessive play or damage are all too common.
CONCENTRICITY IS CRITICAL
Obviously when the clutch relies on friction, concentricity between flywheel and clutch housing is critical if rapid wear is to be avoided. You would not believe the horrors I have seen on attempted clutch jobs. These include missing spigot bearings, broken carriers due to gearbox misalignment and even the driven plate fitted the wrong way round.
Being of relatively large mass individual parts and the complete assembly must be balanced to avoid torsional vibration. The correct type of torsion damper is also important.
The main purpose of the clutch is to allow smooth takeoff and to transmit and interrupt power. While the clutch slips a little during takeoff, only minor heat is generated, but drag-type starts cause excessive heat and rapid wear.
The flywheel and pressure plate are driving members and the friction plate is the driven member. You will find a flexible centre between the hub and its steel disc. This will have up to eight springs to ensure smooth torque delivery. The clutch plate is fitted between pressure plate and flywheel. The driving and driven members were once kept in contact by coil springs, but now a diaphragm spring is generally used.
When the clutch pedal is depressed by a clutch fork it contacts the spring fingers of the diaphragm making the spring pivot around the inner pivot ring and dishes the fingers towards the flywheel. The outer circumference of the spring then lifts the pressure plate away from the driven disc.
POORLY ADJUSTED CABLE
Before we approach the subject of clutch removal, it is wise to ascertain that the clutch is indeed at fault. For example, judder on take-up could be due to loose or worn engine/gearbox mountings. Worn CV joints or incorrectly adjusted foot pedal have caused many an unwarranted clutch removal.
On Beetles, for example, a poorly adjusted or stretched cable could bring annoying symptoms as could incorrect pedal travel. Other possibilities are insecure rear axle, or, silly as it sounds, a loose exhaust knocking against the under body. Check also the semi-elliptic spring mountings. Get a knowledgeable second opinion before getting into the heavy removal bit.
When a clutch won’t disengage, the disc hub may be seized on the gear spline or clutch disc warped.
Next week I shall describe safeguards during clutch renewal. - Star Motoring