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Pelican Technical Article:

Porsche 944 Clutch Master
and Slave Cylinder Replacement
Jared Fenton

Difficulty Level: 3
Difficulty scale: Adding air to your tires is level one
Rebuilding a Porsche 944 Engine is level ten

 
     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. Let’s begin with the clutch master cylinder. This is located on the driver’s side of the car, just to the right of the brake master cylinder/brake booster. In order to remove it, you’ll first need to remove the spring clip that secures the pushrod from the cylinder to the clutch pedal arm. Open the driver’s side door and wiggle yourself in up under the dash near the pedals. You’ll 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. You’ll need to use a small screwdriver to gently pry the lip up then push the clip off. Unfortunately, it’s one of those things that you won’t 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. You’ll 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. You’ll 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 that’s left at this point is to re-attach the starter and battery and set the car down and you’re good to go.

     If you would like to see more technical articles like this one, please continue to support Pelican Parts with all your parts needs.  If you like what you see here, then please visit our online BMW catalog and help support the collection and creating of new and informative technical articles like this one.  Your continued support directly affects the expansion and existence of this site and technical articles like this one.  As always, if you have any questions or comments about this helpful article, please drop us a line.

 
Figure
Figure 1
The first step is to access the clip that holds the clutch master cylinder pushrod to the pedal arm. Climb underneath the driver's side dashboard to access the pedals.
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Figure
Figure 2
Shown here is a close-up of the clutch pedal arm. You can see the pushrod for the clutch master cylinder (red arrow) this attaches to a pivot on the clutch arm and is secured by a spring clip. Unfortunately it's one of those things that's almost impossible to get a picture of while installed. Reach up around the clutch arm (green arrow) and pull up on the clip to slide it off. Once removed, pull the pushrod off the clutch arm.
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Figure
Figure 3
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 (green arrows) and carefully pull the diaphragm and vacuum lines off. Also remove the small vacuum line going to the diaphragm (purple arrow). Also remove the two Philips screws (yellow arrows) and remove the black plastic cover.
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Figure
Figure 4
With the black plastic cover removed, separate the wiring harness connector. This will allow some slack in the wiring harness and help with access below.
Large Image | Extra-Large Image
Figure
Figure 5
Shown here are the vacuum diaphragm and lines removed to gain access to the cylinder below.
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Figure
Figure 6
You may also need to pry one of the cable connectors off the firewall to allow some more slack in the wiring harness.
Large Image | Extra-Large Image
Figure
Figure 7
Remove the 8mm nut holding the upper metal clutch hose to the firewall. This will allow a bit of give in the line when trying to remove the master cylinder.
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Figure
Figure 8
Now, under all of this is the clutch master cylinder. It's not easy to get a picture of it installed but the green arrows show the location of the two 13mm nuts that hold the cylinder to the firewall.
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Figure
Figure 9
Use a 13mm socket with a universal joint to remove both nuts holding the mater cylinder to the firewall.
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Figure
Figure 10
With the nuts removed, carefully pull the old master cylinder out. As you do, cut the metal crimp fitting on the feed line (yellow arrow) and remove the 12mm fitting on the pressure line with a flare nut wrench (green arrow).
Large Image | Extra-Large Image
Figure
Figure 11
Now lay the new master cylinder next to the old one. You will need to transfer the metal block (green arrow) from the old push rod onto the new one.
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Figure
Figure 12
Position the new clutch cylinder in place 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.
Large Image | Extra-Large Image
Figure
Figure 13
Use a hose clamp to secure the clutch feed line to the new clutch master cylinder. This replaces the crimp style clamp originally on there.
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Figure
Figure 14
Here's a trick I like to use to get nuts started on threads you can't reach by hand. 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.
Large Image | Extra-Large Image
Figure
Figure 15
Shown here are the nuts holding the new clutch cylinder to the firewall. Once you have the nuts started on the threads, tighten them down The grease will also help to protect the threads from any corrosion as well.
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Figure
Figure 16
Here is the new 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.
Large Image | Extra-Large Image
Figure
Figure 17
Here is a new clutch fluid hose. It's a good idea to change this 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.
Large Image | Extra-Large Image
Figure
Figure 18
Now 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. You'll need to remove the 8mm and 13mm nuts on the electrical connections (green arrows) and set them out of the way. Now remove the two 19mm bolts holding the starter to the clutch housing. In this picture, you can see one of the bolts (purple arrow). The other bolt is on the other side of the starter (yellow arrow). This bolt will require a open end wrench to remove due to the space around the nut being tight.
Large Image | Extra-Large Image
Figure
Figure 19
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 (yellow arrow). Then remove the two 13mm bolts holding the slave cylinder to the clutch housing (green arrows).  
Large Image | Extra-Large Image
Figure
Figure 20
Shown here is the upper clutch hose connection. You'll want to hold the clutch hose stationary with a 19mm wrench (green arrow) while you loosen and remove the 12mm threaded fitting from the top (yellow arrow).
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Figure
Figure 21
Here's another shot of the upper clutch hose connection shown in relation to the oil filler cap.
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Figure
Figure 22
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 (green arrow). 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.
Large Image | Extra-Large Image
Figure
Figure 23
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.
Large Image | Extra-Large Image

 

Comments and Suggestions:
Alfa SamComments: I just replaced the Clutch MC on a '88 NA 944, How important is it to pull the rod off the clutch pedal? There is a wall of plastic next to the clutch pedal that won't allow the rod to come off the stud on the pedal. Can I leave the rod on the pedal and just replace the MC and the rubber boot and connect the old rod to the MC when installing it on the firewall?
February 3, 2014
 Followup from the Pelican Staff: I suggest removing the rod. This way you have more space and should be able to get things in and out easier. - Nick at Pelican Parts  
the+nbu_dudeComments: It's all much easier if you remove the driver's seat before starting the repair of the master cylinder.
October 10, 2013
 Followup from the Pelican Staff: Thanks for the additional Info. We appreciate it.
- Nick at Pelican Parts
 
MRPComments: What is the size of slave cylinder bleeder screw, can't find it anywhere.
December 16, 2012
 Followup from the Pelican Staff: M6 x 1.0 - Nick at Pelican Parts  
mikeComments: To remove clip easier from clutch pedal remove drivers seat much easier access
November 17, 2012
 Followup from the Pelican Staff: Thanks for the input on this one. We appreciate the help.
- Nick at Pelican Parts
 
CavemanComments: This was by far the most informative information I've ever found on the internet. My master and slave are fixed, the system has been bled, and my clutch pedal seems to be working perfectly. Now, I have another problem. My car won't start. Could it be possible that when I removed my starter I may have damaged it or leaked some brake fluid on it causing it not to work? While doing this process, I also changed my valve cover gasket, seals, and spark plugs. I'm not sure my spark plugs are in the correct order. I've ordered a new starter, probably need one anyway, but can you help me with the firing order on my spark plugs? I can't find any information on this anywhere for a 1987 Porsche 944 s. Any help would be appreciated! Thanks!
June 20, 2012
 Followup from the Pelican Staff: See attached image of firing order. - Nick at Pelican Parts
Scott LComments: When I click on "Fig. 12" "Larger Image" I get Fig. 13's image.

Also, you are showing a "late" 944 non-turbo. The early cars '83 to '85/1 have a slightly different setup.

Also, bleeding on the 85/2 and later cars is a pain because the brake master reservoir has a smaller section that is a "dam" and relies on car motion to splash and refill it. This was a revision to prevent the entire reservoir from draining should the clutch master or slave leak You can barely see the dam area inside the main reservoir, just next to where the clutch master refill hose attaches to the brake master reservoir. In order to bleed the system and keep this section full of fluid, it is necessary to not only completely fill the reservoir, but also to have someone or something hold the reservoir in a tilted attitude - tilted toward the driver's side. This allows the fluid to spill into the dam section. You should also observe the fluid level closely. It is VERY easy to empty this dam. If you do, you will have to re-start the whole process. If I am using the pedal to bleed the system, I would re-check the level on EACH stroke. If I am using a pressure bleeder, I am VERY careful to not bleed more than a CC or two between level rechecks. You will need to "shake" the reservoir to refill as well as maintain a "full to the brim" reservoir. Keep the cap/float off until the system is bled.

IMPORTANT - While you are at it, check the feed hose from the reservoir to the clutch master! It MUST have a fabric cover that is blue in color. I have two 944s that someone changed the hoses. They collapsed and locked up the clutch system! If yours in not as described, run, don't walk, to your nearest Porsche dealer and get the correct hose!
April 28, 2012
 Followup from the Pelican Staff: Thanks for the input on this one. We appreciate the help.
- Nick at Pelican Parts
 
StephinComments: ive tried everything to bleed the system but i still cant get the pedal to return. i did the oil can routine and put fluid through the slave cylinder bleeder but the fluid gets built up and returns to the oil can.
January 17, 2012
 Followup from the Pelican Staff: I would try to pressure bleed it from the slave cylinder up to the master. There is such a short throw on the clutch master it can be hard to bleed. - Nick at Pelican Parts  
RodComments: Well, I swapped both the master cylinder and the slave cylinder, now I'm stuck at the bleeding portion. I don't have a pressure pump for the resvoir, so I'm having my wife pump the clutch pedal, although it hits the floor everytime. I've been following a Haynes manual and this doesn't seem to be bleeding the system at all. Got any ideas?
October 29, 2011
 Followup from the Pelican Staff: Can you get a pump to bleed from the slave cylinder to the master I find this works great. - Nick at Pelican Parts  
Chris JComments: wow i wish i would've seen the greese trick sooner because the nuts were giving a huge problem. There's just not enough room to tighten the nuts. My only concern is transferring the block bc i didnt count the threads before i took it off. So how do i measure the distance now?
September 29, 2011
 Followup from the Pelican Staff: Try to get it in the middle of the threads. You may have to adjust it or fine tune as you bleed the system. See the attached photo for reference. - Nick at Pelican Parts
BillComments: Great write up with excellent photos. I put nine hours into just returning a new master cylinder back into the correct location. The Porsche engineers must still be laughing about his one.
May 24, 2011
 Followup from the Pelican Staff: Thanks for the feedback. Glad we could help.
- Nick at Pelican Parts
 
Mark ChapmanComments: Hi, have found your description very useful, however, apart from the obvious location of the master cylinder, are the parts the same for a English spec Aug '86 944 2.5 non turbo?

regards

mark.
December 27, 2010
 Followup from the Pelican Staff: I think they are the same, if that is what you're asking. I'm not really sure what the question is? - Wayne at Pelican Parts  
ChrisComments: Sorry, forgot the car info. 1990 944 S2. Thanks

July 10, 2010
 Followup from the Pelican Staff: Thanks, got it. - Nick at Pelican Parts  
ChrisComments: I'm trying to take off the spring clip connecting the master cylinder pushrod to the clutch arm and can't do it. There is literally no room, even using a small screwdriver. If I did manage to get it off, how would I get it back on? I would appreciate any advice or helpful hints. Thanks

1990 944 S2. Thanks

Chris
July 10, 2010
 Followup from the Pelican Staff: Yes, those things can be a bitch. All I can say is that you might be able to use some special needle-nose pliers to do that. The same situation exists when trying to replace hood shock spring clips on the bottom of some 911s - next to near impossible. I replaced the shock clip on my 959 by getting a dowel and cutting a slit in the end to hold the pin (had to make my own tool). - Wayne at Pelican Parts 

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