Clutch Master Cylinder Replacement – 2.5L NA

Overview

This guide outlines the procedure to replace the clutch master cylinder on all Porsche 944 variants with an 8-valve engine configuration, covering both pre-1985.5 (1983–1985.5) and 1985.5 onwards (1986–1988) variants. The clutch master cylinder is critical for transmitting hydraulic pressure to engage and disengage the clutch. Replacing it ensures smooth clutch operation and prevents fluid leaks. Follow these steps carefully to maintain your vehicle’s performance.

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Tools Required

• Work light
• 10mm (3/8 inch) socket
• 13mm (1/2 inch) socket
• Socket wrench
• Socket extensions
• Universal adapter
• Needle nose pliers
• Slip joint pliers
• 12mm (15/32 inch) flare nut wrench
• Rags
• Ziploc bags
• Motive pressure bleeder or clear plastic tube
• Catch pan
• 7mm (9/32 inch) wrench
• Paint pen or nail polish
• 13mm (1/2 inch) box/open wrench
• Turkey baster
• Jack stands
• Hydraulic jack
• Side cutters

Parts Required

• Clutch Master Cylinder (Pre-85.5): 477-721-171
• Clutch Master Cylinder (85.5 Onwards): 944-423-149-00
• Gasket: 928-423-191-00
• Bushing/Slide Bearing (Pre-85.5): 999.924.002.40
• Bushing/Slide Bearing (85.5 Onwards): 999-924-039-00
• Blue Brake Reservoir Hose (approximately 2 feet): N/A
• Stainless Hose Clamps: N/A
• Brake Fluid (ATE Super Blue recommended): N/A

Step-by-Step Procedure

Step 1: Prepare the Vehicle

1. Raise the front of the car using a hydraulic jack and secure it on jack stands to access the clutch slave cylinder for bleeding later. This also provides a comfortable working height to avoid strain.
2. Place rags around the brake fluid reservoir and under the clutch master cylinder to catch any spills, protecting the paint from corrosive brake fluid.

Step 2: Remove the Pedal Cluster Cover

3. Locate the plastic cover over the clutch pedal cluster, which protects the wiring and connecting rod.
4. Using a 10mm (3/8 inch) socket, remove the three nylon nuts securing the cover (two on the left edge, one on the right rear corner, as viewed from behind the vehicle looking forward).

5. Remove the cover and store the nuts in a Ziploc bag to prevent loss.

Step 3: Disconnect the Clevis from the Clutch Pedal

6. Locate the spring clip on the clutch pedal where the clevis connects.

For Pre-85.5 models:
Use needle nose pliers to pull down on the spring clip and remove it from the post on the clutch pedal assembly. Pull the clevis straight off the post, retaining the plastic bushing (999.924.002.40). Replace the bushing if damaged.

For 85.5 Onwards models:
Remove the spring clip using needle nose pliers. Push the clevis bolt (944-423-387-00) out through the right side (left as you face the pedal). Retain the plastic bushing (999.924.039.00) and replace if damaged.

7. Mark the clevis connection point on the master cylinder push rod with a paint pen or nail polish to aid reassembly.

For Pre-85.5 models:
Measure and record the distance from the master cylinder mounting plate to the center of the clevis mounting hole before removing the clevis. This ensures proper pedal adjustment during installation.

8. Store the spring clip, clevis, bushing, and bolt (if applicable) in a Ziploc bag.

Step 4: Remove Brake Fluid and Disconnect Lines

9. Use a turkey baster to remove most of the brake fluid from the brake fluid reservoir to minimize spills.
10. Loosen the hose clamp on the blue brake reservoir hose using slip joint pliers. Carefully remove the hose from the reservoir, avoiding damage to the plastic nipple. Use side cutters to remove factory hose clamps if necessary, and replace with stainless hose clamps.
11. Using a 12mm (15/32 inch) flare nut wrench, disconnect the solid line from the front of the clutch master cylinder. Push the line aside to allow removal of the cylinder.

Step 5: Remove the Clutch Master Cylinder

12. Using a 13mm (1/2 inch) socket with a universal adapter, remove the two bolts and concave washers securing the clutch master cylinder to the firewall. Place a magnet near the socket or stuff rags below to catch falling parts.

13. Check the paper gasket (928-423-191-00) for tears. Replace if damaged to ensure a proper seal.

14. Using slip joint pliers, gently pull the clutch master cylinder away from the firewall. Angle it upward to remove the cylinder, boot, connecting rod, and clevis as a unit.

15. Ensure the angle pipe at the top of the cylinder remains intact. If it breaks, replace the cylinder with a new OEM unit (Pre-85.5: 477-721-171; 85.5 Onwards: 944-423-149-00).

Step 6: Prepare the New Clutch Master Cylinder

16. Remove the new clutch master cylinder from its packaging and remove the plastic cap protecting the threads on the front.
17. Transfer the clevis and stop nut from the old cylinder’s push rod to the new cylinder.

For Pre-85.5 models:
Adjust the push rod length to match the measurement recorded in Step 3, then lock it with the stop nut.

For 85.5 Onwards models:
Adjust the push rod/clevis length (A) to 147.0 mm (5.79 inches) for left-hand drive (LHD) or 109.5 mm (4.31 inches) for right-hand drive (RHD), adding 3 mm (0.12 inches) to account for the firewall thickness. Lock with the stop nut.

Step 7: Install the New Clutch Master Cylinder

18. Cut 16–18 inches (40.6–45.7 cm) of new blue brake reservoir hose . Attach it to the clutch master cylinder’s angle pipe with a stainless hose clamp , tightening just enough to secure without damaging the pipe. Loosely attach the second clamp.

19. Install the new clutch master cylinder with the hose attached to the firewall, ensuring the new gasket (928-423-191-00) is in place. Have a helper guide the push rod to align with the clutch pedal to avoid jamming.

20. Secure the cylinder with the two 13mm bolts and concave washers, tightening to 25 Nm (18 ft-lbs). A 1/4-inch drive socket may work without a universal adapter for easier access.

21. Reconnect the solid line to the front of the cylinder using a 12mm (15/32 inch) flare nut wrench. Work carefully due to limited space.

22. Attach the blue hose to the brake fluid reservoir, ensuring not to overtighten the clamp to avoid breaking the plastic nipple.

Step 8: Reconnect the Clevis

23. Under the dash, install the clevis, plastic bushing, and spring clip (or bolt for 85.5 Onwards models) to the clutch pedal.

For Pre-85.5 models:
Slide the clevis onto the pedal post, insert the bushing (999.924.002.40), and secure with the spring clip.

For 85.5 Onwards models:
Insert the clevis bolt (944-423-387-00) through the pedal and clevis, add the bushing (999.924.039.00), and secure with the spring clip.

24. Ensure the clutch pedal has approximately 3 mm (1/8 inch) of free play before engaging. Adjust the push rod if necessary after bleeding.

Step 9: Bleed the Clutch System

25. Fill the brake fluid reservoir with fresh brake fluid to above the minimum line.
26. Attach a Motive pressure bleeder to the reservoir, pressurize to 10–15 psi (0.7–1.0 bar), and check for leaks. Fix any leaks before proceeding.
27. Add 1 quart (0.95 liters) of brake fluid to the bleeder and pump to 15 psi (1.0 bar).
28. Under the car, attach a clear plastic tube to the clutch slave cylinder’s bleed nipple. Use a 7mm (9/32 inch) wrench to open the nipple, allowing fluid to flow into a catch pan. Watch for air bubbles.
29. Close the nipple once the fluid flows without bubbles, then remove the tube and wrench. Clean any spills.

Step 10: Final Checks and Test Drive

30. Remove any rags from the clutch master cylinder area.
31. Test the clutch pedal for resistance and spring-back. It should feel firm and return smoothly.
32. Lower the car from the jack stands.
33. Test drive the vehicle for approximately 5 miles (8 km) to confirm proper clutch operation, checking for smooth engagement and no slipping.

Post Procedure Checklist

• Verify the clutch pedal has 3 mm (1/8 inch) of free play and engages smoothly.
• Check for leaks at the clutch master cylinder, reservoir hose, and slave cylinder.
• Ensure the brake fluid level is between the minimum and maximum lines.
• Confirm the clutch engages and disengages properly during the test drive.

Sources

• Clark’s Garage
• Pelican Parts Technical Articles
• Porsche 944 Workshop Manual