Always renew the seals whenever you dismantle the master cylinder or slave cylinder.

Always renew the seals whenever you dismantle the master cylinder or slave cylinder.

There is usually a rubber dust cover at the pushrod end of the cylinder. Pulling this back along the pushrod usually reveals a circlip at the mouth of the cylinder which acts as a rear stop for the piston. Push the piston in, then release the circlip - it may or may not need special circlip pliers.

The spring inside the cylinder should now push the piston out. If it does not, push the piston down against the spring pressure and then release it quickly.

Remove all the internal parts, carefully noting the order in which they fit together. Keep them in a clean container.

Wash the cylinder with methylated spirit or clean hydraulic fluid. Dry it with a lint-free cloth and examine the bore for corrosion, pitting or scratching. If there is any damage, buy a new cylinder.

The service kit includes a cup seal which fits next to the piston, and a smaller valve seal which goes at the end of the valve stem.

To free the old seals, unfasten the spring retainer (also called a 'thimble' because of its shape). It may have a prong on it; straighten this with a thin screwdriver to free the retainer. Remove the valve and piston seals, noting which way round they fit. On a typical cylinder the refitting order is:

Fit the new valve seal to the valve stem, then fit the spacer and spring retainer to the valve stem;Fit the seal to the piston (cup towards spring), then the spring assembly to the piston;Gently push the retainer prong down to lock it.

Details differ slightly from one cylinder to another. Assembly instructions are often supplied with the new kit.

Finally, lubricate the cylinder bore and the internal parts with fresh hydraulic fluid, then slide the piston in.

The service kit usually includes a sachet of special grease for use on rubber. Squeeze this into the recess in the outer end of the piston. Do not use ordinary grease.

Fit the pushrod and washer, and fasten them in with the circlip, making sure it seats properly in its groove. Slide the rubber cover into place and refit the cylinder.