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Servicing the RV8 clutch master and slave cylinders
Peter Garton (Woodcote Green 1238) from Germany provides a useful guide to maintaining the clutch master and slave cylinders. (Aug 07)

When the clutch pedal suddenly goes partially to the floor, two culprits are the usual cause, namely: the master cylinder or the slave cylinder. Repair kits and new units for both master and slave cylinders are readily available from sources such as Brown & Gammons, Clive Wheatley or Past Parts so the job is one of diligent diagnosis.

Step one is to go for the slave cylinder under the car
When one takes the slave cylinder apart there is little to discern, but when one looks carefully into the cylinder itself, there is often a slight uneven ridge felt by one's finger about 1 inch down - see photo! In my case it was caused by rust which had formed whilst the car was standing unused for many months in Japan. Looking very carefully at the plunger/piston assembly one can see that the seal is not perfectly round and has been deformed by friction with the rust line. These defects will allow fluid to leak past the seals when under pressure during the operation of the brakes so that the clutch pedal will go down floorwards without proper function. The repair kit completes the repair!

Step two is to check the master cylinder
The master cylinder, visible from under the bonnet just above the steering column, is a second cause for concern because of disintegrating seals. A telltale sign that something is not right, is a black residue on the surface of the brake fluid when one unscrews the top cap. As can be seen from the photo, the small end seal has clearly deteriorated. The piston also needs to be cleaned and polished to remove the microscopic layer of stain covering 80% of the surface. Here again the repair kit completes the repair!

When the problem occurs, it is wise to go for the two above items and overhaul both at the same time.


Master cylinder plunger/piston mechanism piston discolouration which can be polished. (Photo: Peter Garton)


Master cylinder plunger/piston end seal disintegration. (Photo: Peter Garton)