Slipstream - August 2002

More documents

Recommendations

Info

Hydraulic Clutch Master Cylinder - Part 1: Inspection By Michael Wingfield Photo by Michael Wingfield Everything You Ever Wanted to Know About Your Hydraulic Clutch Master Cylinder, But Were Afraid to Ask (Part One) This three-part article covers the inspection and replacement of a hydraulic clutch master cylinder in the front-engine, water-pumping family of Porsche cars. Part One details the identification and inspection of a hydraulic clutch master cylinder for the purpose of identifying leaks. Part two of this article covers the steps to remove the hydraulic clutch master cylinder for replacement or rebuilding. Finally, Part Three of this article describes the installation of the hydraulic clutch master cylinder and bleeding the hydraulic clutch system. Have you ever spent time looking for fluid leaks in your car? If you participate any of the PCA driving events, you have seen a car technical inspection form (tech sheet). One of the items addressed on the tech sheet focuses on fluid leaks. Specifically, the Driver’s Education (DE) tech sheet states: Fluids – NO DRIPPING LEAKS of any fluid of any type; appropriate levels and proper fluid types The Autocross (AX) and Time Trial (TT) tech sheet has similar wording, but implies the fluid be checked in the engine compartment. I expect most people look inside the engine bay, under the car, and possibly in the trunk for fluid leaks when inspecting a car for a PCA driving event, or as part of regular highway maintenance. But how often have you looked inside the passenger compartment for fluid leaks? If your car has a firewall-mounted hydraulic clutch master cylinder, then you should also inspect the foot-well of your car for clutch master cylinder leaks. These hydraulic clutch master cylinders appear on the 924S, 928, 944, 951, and 968 series cars. Note that the early 924 and 931 series cars had a cable-driven mechanical clutch, so this article does not apply to those cars. This article covers the inspection and the replacement of the hydraulic clutch master cylinder in the above-mentioned series of cars, and details the steps as performed on my 1986 951. Figure 1 Inspection Inspect the clutch master cylinder, the high-pressure line, and the brake fluid feed line for leaks by looking inside the engine bay. The clutch master cylinder mounts to the firewall, located on the driver side and slightly below the brake master cylinder and brake booster. Depending on the year, model, and specific options on your car, the clutch master cylinder may be easily visible or considerably hidden beneath numerous hoses and other devices. ...inside the passenger compartment for fluid leaks . . . Perhaps the best method for locating the clutch master cylinder is to identify and follow the clutch fluid feed hose, colored light blue if a Porsche part, from the driver side of the brake fluid reservoir down to the top of the clutch master cylinder. For example, Figure 1 shows the placement of a very well hidden clutch master cylinder in my 1986 951. Within Figure 1, label “A” identifies the brake fluid reservoir, label “B” identifies the brake booster, and the arrows from label “C” point to the blue gravity feed hose from the side of the brake fluid reservoir to the top of the clutch master cylinder. Note that the clutch master cylinder is not directly visible, but well hidden behind other components. Check the forward end of the clutch master cylinder for leaks at the high-pressure line (looks like a steel brake line). Also check the top of the clutch master cylinder for leaks from the blue hose supplying fluid. This top hose connection has a plastic fitting set in a rubber seal. The rubber seal works as a stress relief and vibration damper for the blue hose connection. Finally look at the firewall (rear) end of the clutch master cylinder for any signs of leakage into the engine bay. To inspect the pushrod end and the bellows of the clutch master cylinder, look up inside the foot well of the interior of the car, between the clutch pedal and the firewall. If the clutch master cylinder is leaking from the piston end of the cylinder, the bellows will trap the fluid for a while. Figure 2 However, actuating the clutch pedal will eventually cause the fluid to leak onto the sound proofing material on the firewall immediately below the bellows. Figure 2 illustrates the clutch master cylinder bellows and pushrod as viewed from inside the foot well. Within Figure 2, label “A” identifies the bellows on the push rod that connects the clutch piston to the clutch pedal; label “B” identifies a stain caused by brake fluid leaking onto the sound proofing material on the firewall. 12
If you discover fluid in or on the bellows, or a stain on the sound proofing material (especially a damp stain), then you should replace the clutch master cylinder. While not a difficult task, replacing the clutch master cylinder does require many different but common tools and the ability to contort fingers and other body parts into abnormal positions. Having a pair of small hands to assist you will also be of great benefit. Tools Before beginning the task of removing and replacing a leaking clutch master cylinder, it is good practice to take inventory of your available tools. If you are like me, all too often you start a job only to find that you are missing a tool necessary to completing the task. Below, appears a list of the tools needed to replace the hydraulic clutch master cylinder. As mentioned above, the tools are common, but you will need many. Along with each tool appears a brief description of the use for the specific tool: Miscellaneous tools: Common screwdrivers – hose clamps Phillips screwdrivers – hose clamps, engine pan Vice grips – to pinch fluid hose Brake bleeder hose & fluid catch container – system bleed Utility knife – to cut reservoir hose Optional (but recommended) i. Large rubber hammer – always handy ii. Silicone sealant – alternative to a new gasket iii. Dielectric grease – electrical connections iv. Rubber brake line plug – prevent leaks v. Brake system pressure bleeder – system bleed Wrenches: 7 mm – clutch slave bleeder valve 8 mm – starter hot wire, clutch master cylinder pushrod 12 mm brake line wrench – high pressure line to clutch master cylinder 13 mm – starter ground, pushrod lock nut 17 mm - starter heat shield 19 mm – starter mounting bolts Sockets: 8 mm deep – starter heat shield 10 mm – engine pan bolts, clutch master cylinder mounting nuts 12-inch socket extension Socket Universal swivel joint Ratchet Parts Below appears a list of parts needed to replace the clutch master cylinder. The parts apply specifically to my 1986 951, so your specific part number may vary. Clutch Master Cylinder (PN: 477.721.171) Gasket (PN: 928.423.191.00) Reservoir hose (PN: 999.181.021.50) Brake fluid This concludes Part One of this series. Next time, in Part Two, we remove the leaking hydraulic clutch master cylinder. • Increased Horsepower • Lower Temperatures • Superior Protection • Longer Oil Life • API Certified the performance oil that outperforms Top racers and performance shops know that Royal Purple Motor Oil will give them a performance advantage-and now you can enjoy the same benefits! Royal Purple allows your engine to run with less friction, producing more horsepower and offering superior protection. Royal Purple is the choice of champions; try it today and Feel the Performance! Military Distribution: North Texas Lubricants 1-800-364-3025 www.royalpurple.com 13
Page 1 and 2: www.pca.org/mav
Page 3 and 4: www.pca.org/mav Volume 40, August 2
Page 5 and 6: 3
Page 7 and 8: Prez Says by James Shoffit, Maveric
Page 9 and 10: Email: mayos@imagin.net or FAX at (
Page 11 and 12: Happy Hour At Saltgrass by Craig Sm
Page 13: Maverick Region invites you to our
Page 17 and 18: n - Motorsport Ranch - June 2002 Ph
Page 19 and 20: Concours 101 By Gary Coots About 20
Page 21 and 22: June 1 Tech Session at Park Place B
Page 23 and 24: Photo by Kevin Hardison Time Trial
Page 25 and 26: Copper Canyon Fest By Charlie Davis
Page 27 and 28: 4 th Annual CNS Classic Ride Show S
Page 29 and 30: New Wheels If you have any changes
Page 32: Jan Mayo, Slipstream 2973 Timbercre

Slipstream - August 2002

Create successful ePaper yourself

Delete template?

Save as template?