Clutch Master Cylinder Replacement

Introduction

This procedure was contributed by Terry Jenner.

The clutch master cylinder is mounted on the firewall and connected to the clutch pedal via a push rod and clevis arrangement. There are two distinct pedal assembly designs depending on model year:

• Early 944 (1982–89): The clevis attaches to a post on the pedal arm. Push rod length is set by measuring the original before removal and replicating it on the new cylinder.
• Late 944 (1990–91) and all 968: The clevis attaches via a transverse bolt through the pedal arm. Push rod length must be set to a specific dimension (Distance A) during installation.

Note: Confirm which pedal assembly type your car has before beginning. The clevis connection method differs and affects the installation procedure.

Tools

• 12mm flare nut wrench
• 13mm socket with universal joint adapter
• Socket wrench
• Metric open-end wrenches
• Ratchet and extension
• Drain pan
• Rags or shop towels
• Calipers or ruler (for push rod measurement)
• Pressure bleeder (10–15 psi) or assistant for bleeding
• 7mm wrench (for slave cylinder bleed nipple)

Parts

Part Description	Porsche Part Number
Clutch Master Cylinder (early 944, 1982–89)	477-721-171
Clutch Master Cylinder (late 944, 1990–91; 968)	944-423-149-00
Gasket	928-423-191-00
Bushing/Slide Bearing (944, 1982–88)	999.924.002.40
Bushing/Slide Bearing (944, 1989–91; 968)	999-924-039-00
Blue Brake Reservoir Hose (approximately 600mm / 2 feet needed)	N/A
Stainless Hose Clamps	N/A
Brake Fluid (DOT 4)	N/A

Removal

1. Remove the plastic cover panel below the pedal cluster inside the passenger compartment. This exposes the clutch master cylinder connecting rod and clevis attachment at the pedal.

2. Early 944 (1982–89): Before disconnecting the clevis, measure and record the exposed length of the push rod. This dimension will be used to set the new cylinder's push rod length during installation.

   Late 944 / 968: No measurement needed at this stage; push rod length is set to the Distance A specification during installation.

3. Disconnect the clevis from the pedal arm:

   • Early 944: Remove the spring clip and slide the clevis off the pedal post. Remove the plastic bushing.
   • Late 944 / 968: Remove the spring clip and drive out the transverse clevis bolt. Remove the plastic bushing.

4. Move to the engine bay. The clutch master cylinder is mounted on the firewall with its body passing through and a gasket seating against the firewall surface.

5. Using a 12mm flare nut wrench, loosen and remove the solid hydraulic line from the front fitting on the master cylinder body. Have a drain pan in place. Plug or cap the line to limit fluid loss.

6. Using a 13mm socket with a universal joint adapter on the socket wrench, remove the two mounting nuts securing the master cylinder to the firewall studs.

7. Pull the master cylinder away from the firewall. The push rod and boot will come with it.

8. Disconnect the rubber brake hose from the angle pipe fitting at the top of the master cylinder body (connects to the brake fluid reservoir). Note the hose routing for reinstallation.

9. Set the old cylinder aside. If reusing the push rod and clevis, transfer them to the new cylinder now.

Installation

1. If the original rubber brake hose from the reservoir to the master cylinder is deteriorated, replace it with new blue brake hose cut to length and secured with stainless hose clamps. Approximately 600mm (2 feet) of hose is needed.

2. Set the push rod length before installing the cylinder:

   Early 944 (1982–89): Adjust the push rod to match the measurement taken during removal. Lock the clevis in position.

   Late 944 (1990–91) and 968: Set Distance A — measured from the car body (firewall surface) to the center of the clevis hole — to the following specification:

   • Left-hand drive (LHD): 147.0 mm
   • Right-hand drive (RHD): 109.5 mm

   Note: If measuring Distance A with the cylinder not yet mounted against the firewall, add 3 mm to account for the thickness of the firewall itself.

3. Place the gasket onto the firewall studs. Guide the master cylinder through the firewall from the engine bay side, feeding the push rod through to the pedal side.

4. Install the mounting nuts with their concave washers (concave side facing the cylinder flange) and torque securely.

5. Reconnect the solid hydraulic line to the front fitting using the 12mm flare nut wrench. Do not overtighten — snug firmly to avoid leaks without distorting the fitting.

6. Connect the blue brake hose from the master cylinder angle pipe up to the brake fluid reservoir. Secure with stainless hose clamps at both ends.

7. Inside the passenger compartment, reconnect the clevis to the pedal arm:

   • Install the new plastic bushing onto the pedal post or through the clevis hole.
   • Early 944: Slide the clevis over the pedal post and secure with the spring clip.
   • Late 944 / 968: Insert the transverse clevis bolt and secure with the spring clip.

8. Fill the brake fluid reservoir to the maximum mark with DOT 4 brake fluid.

9. Bleed the clutch system using a pressure bleeder set to 10–15 psi at the reservoir, or use the two-person pedal method described in clutch-02. The slave cylinder bleed nipple requires a 7mm wrench.

10. Reinstall the interior plastic cover panel below the pedal cluster.

11. Verify clutch engagement and release: the pedal should be firm with no sponginess, and the clutch should engage cleanly without slipping or dragging.