MC – Last issue we were resurrecting a 944 that had been stored for 10 years. The clutch was the next system to consider. On an older 944 the clutch system is fairly simple. Unfortunately, it is located in the front of the car sandwiched between the engine and the central torque tube. This makes access somewhat difficult and after 20 years, you could have a problem after you begin driving the car.
First, let’s take care of age issues that I consider routine maintenance. When you push the clutch pedal down, does it return by itself or do you have to pull it up with your foot? If it goes down but won’t come up, you might have fluid loss, mechanical binding, or an adjustment problem with the “over center” linkage adjustment. If it’s like most I’ve seen, though, it is likely a hydraulic problem.
The clutch hydraulic system receives its fluid supply from the brake master cylinder reservoir. Just like the brake system, rubber parts don’t age well. It is reasonable to expect, if the car is more than ten years old, that you will eventually need to replace both the clutch slave and clutch master cylinders. Since this is a budget job, though, we’ll see what we can do while spending very little money.
To get a look at the clutch master cylinder you will need to be a contortionist and screw your skinny little upper body up under the dash to look at the clutch master boot and linkage. If you find it wet or dripping, the clutch master cylinder will need to be replaced. If it is dry under there, you are in luck! You can wiggle your way out of the car and get underneath the car now. This is fun isn’t it!
Jack up the car, put it on jack stands and look at the side of the bell housing just forward of the starter. You should see a round 40mm rubber plug (or just an open hole where the plug used to be.) Pull the plug out carefully, you’ll want to re-use it later. Through that hole, you can view the action of the clutch slave cylinder while you have one of your buddies push the clutch pedal assuming that the clutch master is producing pressure. If it works, you are in luck…your system is producing some pressure. You should start by bleeding the system (see below) and then checking for proper disengagement. You will still need to plan on replacing the slave and master eventually, but you may be able to buy yourself a little time. Check again for leaks at the master after the bleed. The seal on the master may be deteriorated just to the point that it will hold pressure for a while, but leak down later. If you DON’T plan on performing the maintenance listed below for the slave cylinder, check it REALLY well for leaks after the bleed or you’ll be sorry later.
Even if the system will hold pressure, you can bet your bottom dollar that the innards of the cylinders are not in prime condition after the car has been sitting so long. Even if I was going to replace the slave later, I’d still want to try to clean it out, if only on principle. I would remove the clutch slave from the trans housing. On a bench, dismantle it and clean it well. If the bore is rusty or the rubber boots or seals are ugly, replace it. Typically, the slave cylinder lives only half as long as the clutch master cylinder which is not surprising considering the environment it lives in.
The other clutch components that should be serviced at this time are the clutch fork, pivot shaft, and bearings. In typical Porsche fashion, the pivot shaft runs on needle bearings. These bearings dry out since they are located inside the bell housing and get bombarded by clutch wear particulate. The shaft develops wear pockets where the needle bearings ride on it and between the dry bearings and pocketed shaft, the pedal can feel a little stiff and crunchy on an older 944 (and 911 as well).
You can remove the shaft and lubricate the needle bearings without major disassembly and this is a very smart thing to do. If you find that the shaft is not smooth and a little pocketed , you can gain another lifespan out of it by grinding another “flat” (where the set screw holds it in place) 180 degrees opposite the original flat. With this, the bearing rides on a fresh bearing surface. It only takes a couple of hours on average, and is well worth it in terms of both pedal feel and smooth actuation.
At this point with everything apart take a good look at the clutch and flywheel assembly and see if you can find any chunks of black rubber debris in the bell housing area. If you do, you might as well plan to replace the clutch since the clutch disc is “chunking”. (not a technical term) On many Porsche, the original clutch has a rubber center to dampen vibrations and eventually they fail. It you find no rubber parts, you win and you can start putting it back together.
So you have inspected all the parts, you have the shaft cleaned up, and the slave checked out. If you’re like me and want to maintain everything in beautiful shape, you’ll want to take this chance to clean and prep the bell housing area. The first word of caution is: Do not try to clean the internals with any spray cleaner. If you do, you can contaminate the clutch bearing or wash debris into the clutch. I use a long Q-tip with mineral spirits to clean the rubbing surface as best I can. The lubricant that I use for the bearings is a Wurth product called HSS-2000, a penetrating grease that sprays on with the consistency of WD-40. The carrier fluid evaporates and leaves the gooiest, stickiest grease I have ever seen. While the shaft and clutch slave are out of the car, you should spray some MolyKote dry lubricant on the rubbing surface of the clutch bearing, clutch “fingers” and the clutch bearing support. Now you’re ready to reinstall the slave, although you may want to take the time to clean off all the nuts and bolts, lube up the holes with anti-seize compound, that sort of thing…the next guy to take this apart will thank you, especially if it’s you!
Once everything is back together, you are ready to bleed the system. The first surprise is that when you push the clutch pedal down, it does not return. Remember the over center mechanism? This is the linkage designed to help you keep the clutch pedal down on the floor while you are at a stop light. You have to overcome this linkage and pull the pedal back up to continue your bleeding process. Try a piece of rope wrapped around the pedal.
After bleeding, the pedal should return on its own. If it does not, the mechanism may need adjustment or the master may not be able to hold a “prime”. Occasionally, in spite of your best efforts, you can get everything right and find that the master gulps in air when you release the pedal. Assuming it all works as expected, you have probably spent a full afternoon on this process. But, the clutch action should be silky smooth. If you’re lucky, you won’t have to do it again for years. Oh…and one last thing, if you want that 40mm rubber plug to stay in place, glue it in. MC