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Clutch Master Cylinder Replacement
 
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Pelican Technical Article:

Clutch Master Cylinder Replacement

Steve Vernon

Time:

3 hours3 hrs

Tab:

$70 to $210

Talent:

***

Tools:

13mm, 10mm, 9mm socket, universal joint, extensions, 12mm flared nut wrench, flathead screwdriver

Applicable Models:

Porsche 944 (1983-89)
Porsche 944 S2 (1989-91)
Porsche 944 Turbo (1986-89)
Porsche 944S (1987-88)

Parts Required:

Clutch master cylinder, new fluid, hydralic hose

Hot Tip:

Be patient when removing the clip

Performance Gain:

Reliable shifting and clutch operation

Complementary Modification:

Bleed brake system

The Porsche 944 uses a hydraulic clutch engagement system. There are no cables involved with the actuation of the clutch. When you press on the clutch, pressurized brake fluid moves from the master cylinder through either a metal or rubber line to the slave cylinder mounted on the transmission. This results in a system that takes less physical effort to move.

Although this actually creates a more reliable clutch system, over time, there can be a failure or breakdown of the system if the slave or master cylinder gets old and begins to leak or fail. A spongy feel to the clutch pedal, grinding of gears when shifting, long pedal travel, and hydraulic leaks under the car are all signs that one or more components of the system have failed.

You will need to drain the hydraulic fluid below the level of the supply line attached to the brake fluid reservoir. Get a turkey baster or fluid pump and suction fluid out until it is below the line. Even though you have removed some fluid, there will be spillage of the fluid left in the line and master when you remove it. Be prepared to catch and dispose of it safely.

Even if you are just replacing the master cylinder, you will need to bleed the slave cylinder to get all of the air out of the line. Please see our article on clutch slave cylinder bleeding and perform that work before trying to drive the vehicle.

The clutch master cylinder is located just to the right of the brake booster and under a bunch of EVAP hoses (red arrow).
Figure 1

The clutch master cylinder is located just to the right of the brake booster and under a bunch of EVAP hoses (red arrow).

Before you begin working on removing the master cylinder, you need to free it from the clutch pedal inside the car.
Figure 2

Before you begin working on removing the master cylinder, you need to free it from the clutch pedal inside the car. You are going to be working in very tight quarters under the dash. I recommend that you take the time and remove the driver's seat. Begin by removing the plastic cover that protects the under dash wiring. It is held in place by three 9mm nuts (red arrows).

With the cover removed you can see where the rod for the master cylinder (green arrow) connects to the clutch pedal shaft (red arrow).
Figure 3

With the cover removed you can see where the rod for the master cylinder (green arrow) connects to the clutch pedal shaft (red arrow). It is held in place by a spring clip (yellow arrow).

Pry the spring clip off the shaft (red arrow) and then slide the adjusting block off of the shaft on the pedal (green arrow).
Figure 4

Pry the spring clip off the shaft (red arrow) and then slide the adjusting block off of the shaft on the pedal (green arrow). Do not remove the adjusting block yet, as you will need to measure it to get the correct length for installation.

With the push rod for the master disconnected from the clutch pedal move around to the top of the engine compartment.
Figure 5

With the push rod for the master disconnected from the clutch pedal move around to the top of the engine compartment. You can see where the supply line for the clutch hydraulics attaches to the brake fluid reservoir (yellow arrow). You will need to drain the fluid to below this level before disconnecting. Remember that even though you have removed some fluid, there will be spillage of the fluid left in the line and master when you remove it. Be prepared to catch and dispose of it safely. You can just see the master cylinder in this picture (red arrow).

To remove it you will need to move some of the EVAP components out of the way.
Figure 6

To remove it you will need to move some of the EVAP components out of the way. Disconnect enough of the lines (red arrows) so that you can remove the two 10mm bolts holding the plate on and swing everything out of the way (yellow arrow).

With the EVAP out of the way remove the electrical cover so you can disconnect the wiring harness and give yourself more room to work (red arrow).
Figure 7

With the EVAP out of the way remove the electrical cover so you can disconnect the wiring harness and give yourself more room to work (red arrow).

Disconnect the supply line from the brake fluid reservoir (red arrow).
Figure 8

Disconnect the supply line from the brake fluid reservoir (red arrow). Now is a really good time to replace the line if needed.

Use a 12mm flared nut wrench and disconnect the hydraulic line from the master cylinder (red arrow).
Figure 9

Use a 12mm flared nut wrench and disconnect the hydraulic line from the master cylinder (red arrow). Some fluid is going to spill, so be prepared.

It is a tight fit.
Figure 10

It is a tight fit. Use a 13mm socket with a universal joint and an extension and remove the two 13mm nuts holding the master in place (red arrows) You can now carefully remove the master from the car.

Lay the new master cylinder beside the old one and measure the distance between the end of the rod and the adjustment block (red arrows) Transfer the adjustment block and locking nut to the new master, making sure they are the same length.
Figure 11

Lay the new master cylinder beside the old one and measure the distance between the end of the rod and the adjustment block (red arrows) Transfer the adjustment block and locking nut to the new master, making sure they are the same length.

Before you install the new master some people like to bench bleed the master to help in getting the air out of the system.
Figure 12

Before you install the new master some people like to bench bleed the master to help in getting the air out of the system. While this will help speed up the process, it is not necessary since you are going to have to completely bleed the slave after you install the new master. Please see our article on bleeding your clutch slave cylinder. Installation is the reverse of removal.

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