Image:Clutchdisc.jpg

A clutch disc.

This image was made by w:User:Sonett72 and originally uploaded to w:Image:Clutchdisc.jpg.

This is a typical clutch disc. This particular clutch plate was made by Fichtel & Sachs and fits the Ford Taunus V4 engine in a Saab 95/96/97. It has a number of interesting features:

• The large, flat ring that forms the perimeter of the clutch is the lining. There are two such rings, one on each side. Their surface material is similar to that of brake pads. One lining ring makes frictional contact with the pressure plate, the other faces the flywheel. Clutch discs typically have an orientation; if they are installed backwards, the clutch will not operate properly.

• The lining rings are riveted onto the blades of a fan-shaped part which can only be partially seen in the image. This is called the marcel, and the blades of this part are the marcel springs, not to be confused with the plainly visible coil springs surrounding the center hub. Like the blades of a fan, the marcel springs are somewhat twisted, and the lining rings are riveted to these blades in such a way that when the disc is squeezed between the flywheel and pressure plate, the twisted blades flatten, allowing the disc to compress. A compressible clutch disc provides smoother, more gradual engagement, and reduces chatter.

• Each of the six marcel spring blades has two holes for mounting the lining rings, one hole for each ring. Thus six rivets attach each lining ring to the marcel. In this picture, twelve rivets are visible around the facing ring, but on closer inspection, it's obvious that six of them are deeply recessed: they are in fact rivets belonging to the opposite ring on the other side, visible through large holes in the facing ring. These holes in one ring provide tool access for mounting the other ring to the marcel. This attachment pattern allows the marcel blades to twist and flatten when the rings are compressed together.

• The teeth of the center hub are plainly visible. These fit into splines on the transmission input shaft. By means of these teeth, the disc forces the shaft to rotate, but can move back and forth on the shaft freely. It is possible for the shaft or hub to rust, causing the disk to become stuck to the shaft, which results in intermittent difficulties in shifting.

• A number of 4 coil springs are visible, arranged in a circular pattern around the hub. These damper springs provide elasticity between the toothed center hub and the clutch disc. That is to say, the hub can be slightly rotated independently of the disc, a motion which is stiffly opposed by the compression of these springs. The springs provide cushioning between the engine and transmission, helping to absorb the forces of sudden engagement and vibration.

• The coil springs are held in place by metal folds, cut and bent out from the center plate. One mode of clutch failure is that these folds can wear out, allowing a spring to fall out and become lodged in the clutch, preventing engagement. On two of the springs wear spots can be clearly seen.

Clutch discs typically do not have individually serviceable parts. When a clutch is serviced, the entire disc is replaced as a unit. The lining, marcel springs and damper springs and their housing all are subject to fatigue and wear. A high quality clutch that is operated correctly can last well in excess of 200,000 kilometers.

Either the marcel or damper springs or both may be absent from clutches used for racing, for greater strength, lighter weight and faster shifting.

This image has been (or is hereby) released into the public domain by its author, Sonett72 at the English Wikipedia project. This applies worldwide. In case this is not legally possible: Sonett72 grants anyone the right to use this work for any purpose, without any conditions, unless such conditions are required by law.

File history:

• 21:19, 4 Jun 2005 . . Sonett72 (49901 bytes) (clutch disc)

• Clutch