Mark 111 Clutch Cylinder Replacement
Over time, either the clutch master or slave cylinders can wear out and need to be rebuilt or replaced. The need for replacement is usually evident because of fluid leaks. For the master, you may find fluid leaking on the carpet under the clutch pedal and for the slave you may find fluid leaking under the car. This tip is a step by step replacement process.
Master cylinder replacement
The Mark III master cylinder, pictured below, is Wilwood part 260-3376 (7/8”dia). Available from www.wilwood.com , this unit can be rebuilt with rebuild kit 260-3882. Wilwood also sells a 1” master, 260-3378, that can give you a faster acting/shorter foot stroke clutch at the cost of higher foot pressure, if this change is desired.
To remove or replace the Master, lift and secure the front of the car. Remove the drivers side front tire and the access door at the rear of the drivers side front wheel well. From under the hood, pinch off the rubber hose that runs from the remote reservoir to the master cylinder with hose pinch pliers or similar. Don't pinch so tight as to damage the hose, you only want to stop potential fluid flow. Working through the access hole, disconnect the fluid line and the remote reservoir hose from the master. From inside the foot box, disconnect the clutch pedal return spring and the master actuating rod. Then remove the two bolts that fasten the master to the fire wall. Reverse the process for installation and bleed.
Slave cylinder replacement
The slave is an “installer” part and varies from car to car. Most installers have used one of the three pictured below. If yours is different, you may need to contact the installer for a part number. While you may be able to find a rebuild kit for these cylinders, most opt to buy a new cylinder because the cost is not much more and you avoid any machining or honing.
73286 above is also available at AutoZone under Part Number 12425
To remove the slave, lift and secure the front of the car. From under the hood, pinch off the rubber hose that runs from the remote reservoir to the master (see Master cylinder replacement). From under the car, remove the fluid line and cap it off to help from draining fluid. Remove the slave by removing the two attaching bolts. Make a mental note of how the slave is attached. Some installers use shims or washers under the mounting ears to adjust the slave, some use a homemade threaded rod with a Nylock nut for clutch adjustment and still others use an aftermarket rod with an adjusting nut. No one solution is necessarily better than the other and the easiest solution for reassembly would be to reassemble it as you took it apart. Also make note of the alignment of the actuating rod. It should project “straight” out of the cylinder. If it is not properly aligned (angled to one side), it can cause premature failure of the cylinder. If it is not properly aligned, fabricate a new or modify the current mounting bracket.
For reassembly, push the actuating rod into the slave until it bottoms. Some slaves come with an internal return spring that makes this difficult. It is best to remove the internal spring. It is not needed on a Mark III installation that has a return spring on the clutch pedal. With the piston bottomed, install the slave cylinder. There should be a maximum of about 1/6” clearance between the actuating rod. and the clutch fork while applying some hand pressure to separate them. Depending on how yours is assembled (shims or adjustable rod), make adjustments until the proper clearance is achieved. If there is too much clearance, you may not be able to disengage the clutch. If there is no clearance, you will put undue ware on the throughout bearing. Reattach the fluid line, remove the pinch pliers from the reservoir hose and bleed the clutch system.
When complete, the clutch should be completely disengaged just before the pedal reaches the floor. To test this, start the car, push in the clutch pedal, wait a second or two and then attempt to engage reverse. The gears should not grind. If they do, first recheck to make sure the slave is properly adjusted and bled, Then if further adjustment is needed, adjust the clutch pedal higher via the master cylinder adjusting rod in the foot box. The is done by loosening the jam nut on the adjusting rod, then turning the rod out of the clevis at the pedal and finally retighten the jam nut.
This page applies to most Superformance cars. This link offers an alternative Craig's Cobras Slave Cylinder Project
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