The clutch master cylinder (Land Rover SII to SIII) is mounted on the engine side of the fire-wall, on the clutch pedal box, to which it is attached by two bolts. The clutch pedal operates a push-rod which moves the piston, displacing hydraulic fluid, operating the clutch slave cylinder and hence the clutch itself.
If the master seal is defective, clutch fluid will escape. This might take place slowly, leading to drips and "runs" on the firewall, down the clutch pedal or on the floor under the clutch pedal. (If a falling fluid level suggests a leak, check around both the slave and master cylinders.)
Removing a Master Cylinder
Drain the clutch hydraulic fluid using the bleed nipple on the slave cylinder.
A cover plate on top of the pedal box gives access to the two mounting bolts and the push-rod. It really needs two people to remove the mounting bolts: one in the driver's foot-well to hold a spanner on the bolt head, the other to turn the nut from the engine bay, particularly for the lower bolt. Also disconnect the hydraulic pipe at the master cylinder (and cover to prevent dirt getting in).
With the master cylinder loose, it is possible to disconnect the push-rod from the pedal and to withdraw the master cylinder. It takes a bit of "jiggling" and don't drop fluid on the paint work, but if you do ... quickly wash off with water.
Ideally disassembly should take place somewhere well-lit, clean and dry. On no account should any mineral oil or related product come near the rubber seals or the master cylinder. One approach is to work on top of many layers of newspaper and discard them as they get dirty. Clean up the exterior of the master cylinder using the proverbial "lint free cloth" or paper towels, toilet paper (cheap) etc.
Pushing off the rubber cover gives access to a spring circlip inside the end of the cylinder. Releasing the circlip allows the push-rod piston to be removed, possibly after a little gentle tapping.
Carefully check the cylinder and piston for scores or other signs of wear. If all is well, a new "kit" of rubber seals can be fitted, otherwise the complete master cylinder should be replaced.
The piston assembly consists of (i) the piston itself and its main seal, and (ii) a valve, connected by a rod and spring. When the pedal is depressed the initial movement causes the valve to cover and seal the hole between the fluid reservoir and the master cylinder. Further movement forces fluid down the pipe to the slave cylinder.
The rod is held to the piston by a "clip" which can be released, but beware: the spring can then propel the parts to God knows where unless you are ready for it (the spring is not particularly strong). There are small parts and washers in the valve, so treat them carefully and note how they were assembled!
Remove the old main seal, and carefully fit a new one (the right way round), using rubber grease, care, and delicate language; this offers some opportunity for a stuff-up considering the materials involved. Similarly, replace the small seal in the valve. Reassemble the piston, valve, rod, spring and clip, not allowing any parts to "escape".
Lubricate the cylinder with hydraulic fluid. Introduce the piston assembly into the cylinder but use a gentle rocking motion to persuade the main seal to enter the cylinder. Do not damage its lip.
The push-rod can now be placed in position and the circlip re-fitted to hold the push-rod retaining washer and the push-rod end, in the cylinder.
Refitting the master cylinder to the pedal box is, as they say, the reverse of the removal process. Wriggle the assembly around to mate up to the pedal box, feeding the push-rod into the hole in the pedal arm with the nut and washer, then fitting washer and lock-nut, in the right order. Start the hydraulic pipe fixing into its thread while all is still loose and able to be moved somewhat (beware of crossed threads).
Fit and tighten the fixing bolts - an assistant makes it much easier. Adjust the push-rod so that there is a small amount of pedal play before the piston "takes up"; this is important to allow the clutch to adjust itself as the clutch plate wears. Fill the reservoir with hydraulic fluid, and bleed the system to remove air. Always use new hydraulic fluid.
4WD Vehicles A-Z
4WD Toys & Models
History of 4WDs