| 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 break-down 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.
Replacement of both cylinders is a bit tricky due to their locations. Lets begin with the clutch master cylinder. This is located on the drivers side of the car, just to the right of the brake master cylinder/brake booster. In order to remove it, youll first need to remove the spring clip that secures the pushrod from the cylinder to the clutch pedal arm. Open the drivers side door and wiggle yourself in up under the dash near the pedals. Youll see the pushrod from the cylinder going towards the clutch pedal arm. Reach up and feel the end of the pushrod. There is a tension clip that holds it on. Youll need to use a small screwdriver to gently pry the lip up then push the clip off. Unfortunately, its one of those things that you wont be able to see very well due to the location of the clutch safety switch bracket, but rest assured, the clip is there (See Figures 1 and 2). Just take your time as it can get a bit frustrating doing this all by feel.
In order to remove the clutch master cylinder, you will have to remove some vacuum components and lines to allow access. Loosen the hose clamps and carefully pull the diaphragm and vacuum lines off as shown in Figure 3. Also remove the small vacuum line going to the diaphragm. Also remove the two Philips screws holding the black plastic cover onto the firewall just behind the vacuum diaphragm. With the black plastic cover removed, separate the wiring harness connector. (See Figure 4). This will allow some slack in the wiring harness and help with access below. It also can help if you use a small screwdriver to pry the wiring tie off the firewall (See Figures 5 and 6).
Now follow the clutch hose back along the top edge of the firewall and remove the 8mm nut holding the upper metal clutch hose to the firewall. This will give some slack in the line and help to pull the cylinder out (See Figure 7). Under all of these connections lies the clutch master cylinder. Carefully move the vacuum lines, feed lines and electrical connections aside and locate the two 13mm nuts holding the cylinder to the firewall. These will be difficult to get to due to the clearance under the hood, although you should be able to reach them using a 13mm socket with a universal joint and extension (See Figures 8 and 9). Once the nuts are removed, carefully maneuver the cylinder up and out of the firewall enough to loosen and remove the 12mm fitting for the clutch hose out of the end of the cylinder. Then use a pair of vise grips to clamp off the feed hose and cut the clamp holding the feed hose to the master cylinder (See Figure 10).
Once out, lay the new master cylinder next to the old one. You will need to transfer the metal block with the hole from the old push rod onto the new one. This is the part that mounts to the clutch pedal arm. Make a note of the number of threads on the old pushrod and set up the block on the new push rod with the same number of threads exposed (See Figure 11).
Now position the new clutch cylinder in place, feeding the pushrod through the hole into the passenger compartment. Keep the cylinder right ahead of the mounting studs and thread in the 12mm fitting for the clutch pressure hose. Take caution to make sure you have it threaded in correctly as they can easily cross-thread and strip. Also use a new hose clamp to secure the clutch feed line to the new clutch master cylinder. This replaces the crimp style clamp originally on there (See Figures 12 and 13).
Now slide the cylinder back against the firewall and connect the pushrod back up to the clutch pedal arm from inside the passenger compartment. Now move back to the engine compartment. Youll see that there is no way to thread the two 13mm nuts on by hand. What I like to do in situations like this is to place a dab of grease on the inside of the socket, then place the nut in. This will prevent the nut from falling out of the socket when you try to get it back on the threads. Position the nuts onto the threads and tighten them down. Wipe off any excess grease that may be on the nuts (See Figures 14 and 15). Reconnect the hoses and place the vacuum diaphragm back in place.
Now on to the slave cylinder. As a rule, you almost always want to change the master and slave cylinder at the same time. It's difficult to determine if either the master or slave goes bad when the system fails, and you might end up having to do the job twice. It's also a good idea to change the rubber fluid hose at the same time you change out the master and slave cylinders. In our case, the original fluid hose had cracked and was leaking where the rubber portion met the metal fitting (See Figure 16 and 17).
Jack up the car so you can access the starter. Make sure you use quality jack stands to secure the car up in the air and disconnect the battery. This is important, as you will be removing the cables going to the starter which are live. Due to the layout of the 944, there are a few differences from other cars. For example, the engine is located in the front of the car and the transmission is located in the rear. This provides a good weight balance between the front and rear of the car, resulting in an almost perfect weight distribution. Due to this arrangement, the starter motor is located on the clutch housing plate almost at the bottom of the car as opposed to being mounted on the transmission. Youll need to remove the starter in order to access the slave cylinder which is directly above.
Remove the 8mm and 13mm nuts on the electrical connections to the starter and set them out of the way. Now remove the two 19mm bolts holding the starter to the clutch housing. One bolt will be easily removed with a socket, however the other will require a open end wrench to remove due to the space around the nut being tight. (See Figure 18).
With the starter removed, you will be able to access the clutch slave cylinder. Remove the lower clutch hose connection from the top of the cylinder using a 12mm flare nut wrench, then remove the two 13mm bolts holding the slave cylinder to the clutch housing. Make sure you have a drain pan handy to collect the fluid that will drain out of the clutch hose (See Figure 19). Now move up to the engine compartment and disconnect the old fluid hose. You'll want to hold the clutch hose stationary with a 19mm wrench while you loosen and remove the 12mm threaded fitting from the top (See Figures 20 and 21). Lower the new fluid hose down from the top of the engine and connect it to the metal fitting.
Now get back under the car and make sure that the piston rod of the new slave cylinder seats correctly in the small cup on the end of the throwout arm in the clutch housing. As you fit the slave cylinder, you'll need to compress the piston to get the screws to thread into the clutch housing. Just take your time and make sure that the piston rod is seated. (See Figure 22).
The system now needs to be bled. I like to use the Motive Products Power Bleeder (available from PelicanParts.com) for this task. Attach the power bleeder to the top of the master cylinder reservoir and pump up the pressure in the bleeder. NOTE: DO NOT exceed 1 bar (14psi) doing so can damage the seals in the clutch hydraulic system.. With the pressure bleeder set up, attach a hose to the bleeder valve. Open the bleeder screw and let the system bleed until there are no more air bubbles coming out while a helper pumps the clutch pedal. It's also important to keep an eye on the reservoir level. If the level drops below the clutch feed line, you'll have to start bleeding all over again (See Figure 23). All thats left at this point is to re-attach the starter and battery and set the car down and youre good to go.
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