| Symptoms and Basic Diagnostics: The Clutch Pedal has no Pressure and/or the Pedal goes to the Floor without Engaging the Clutch. Either fluid level is too low to maintain clutch line pressure; or there is a large amount of air in the line that is preventing a buildup of hydraulic pressure. If the fluid is too low or air has entered the system; adding fluid alone will not fix the problem. The system must be bled to eliminate the air pockets which compress and prevent line pressure from being established. Apparent Clutch Line Pressure but no Clutch Disengagement - If there seems to be adequate clutch line pressure at the pedal, but the clutch disc is not actuated, then a mechanical failure should be suspected. Check for a broken pivot ball, or a defective clutch fork. Line pressure can be confirmed from underneath the car by verifying movement of the slave cylinder piston pin as the clutch pedal is depressed. If the pin pushes forward, but the clutch does not disengage, I would suspect a failure in the mechanical parts. When the Clutch Line Pressure Increases After Warm-Up - As the engine approaches operating temperature, the clutch line becomes hot which warms air bubbles in the line. These bubbles expand when heated and create pressure in the line. If the clutch pedal was adjusted properly when the car was cool, but becomes too high (releasing too high off the floorboard) after warming up; then one should look for air trapped in the line. Conversely, if the clutch was adjusted when the engine is warm; the pedal may become too low off the floorboard when the engine cools. This is because the trapped air cools and contracts in volume. The pedal may become so low that engagement of the clutch is difficult or impossible. If this happens, start the engine and wait for the line to heat up. The heated air bubbles may expand and allow for the engagement of the clutch Noticeable Movement or Sinking of the Pedal Height – If the pedal suddenly begins to become soft, where it drops towards the floorboard; I would first bleed the system. It is unlikely your clutch is wearing so fast that you can notice a change in the position of the pedal caused by surface wear of the disc face and pressure plate. However, if shortly after adjusting the clutch adjustment threaded rod, it drops more. I would suspect an air leak in the clutch hydraulic system. The two most likely sources of leaks are the Master Cylinder and the Slave Cylinder. Air leaks may also be sourced to lose couplings or fittings, the metal line, and the flexible hose. Clutch Bleeding Procedure(s): You Will Need - 10 mm flare wrench; two (2) pints of brake fluid; and 2-3 feet of clear plastic hose, 1/8” id. Clear hose is required in order to observe air bubbles as fluid evacuates the system. I use a latex hose sealed to a plastic collection bag. I think it is a hospital item. Two People Needed to Bleed Clutch - I will not explain the bleeding procedure except to say the proper sequence is to first build up line pressure; then open the bleeder valve (while continuing to hold down on the pedal); bleed off some old fluid; then close the bleeder valve. Then repeat the process. There are many posts on how to bleed a hydraulic system. Use the “Search” feature if you are unsure. I will add that you need two (2) people. One person should be inside on the pedal, and another to open and close the bleeder valves. Either person can keep the reservoir filled. Keep the Master Cylinder Full - Never allow the master cylinder to drain below the level of the intake port located at the rear wall of the master cylinder. Air will enter the system and you will have to bleed all the fluid out from that point forward. Four or five (4-5) good pedal pressure bleeding actions will drain enough fluid from the reservoir to allow air into the system. This will drive you nuts!! I think the quick drain of the reservoir is the single biggest problem most of us encounter. Air enters the line because the fluid level dropped, however, when we refill, we don’t realize that new air got into the system. We continue to bleed and bleed, not knowing we have to push that new air bubble the entire length of the system. Sometimes, it seems to take forever to build pressure. Bleeding the Bottom and the Top - First, be advised there are two (2) bleeder valves. One is on top of the passenger side fender well, near the HICAS pump. The second is under the car, on the slave cylinder. You need to bleed both. Most people advise bleeding the bottom valve first. I think maybe because the air bubbles will rise to the top. The topside valve is where the accumulated residual air and would be purged last. However, when bleeding, everyone suggests going back and forth... Gravity Bleed Bottom First - I was advised to begin by gravity bleeding the slave cylinder. Open the slave cylinder bleeder valve one quarter to one half turn (counterclockwise) and allow gravity to drain the fluid out. If no fluid comes out; close the valve, pump the clutch pedal normally five (5) or ten (10) times, and open it again. Do not put any pressure on the clutch pedal. Just open the cylinder bleed valve and let it drain. If still no fluid comes out, then open the upper bleeder valve... This will eliminate the capillary pressure (the suction-like process of holding your finger over the top of a soda filled straw.) in the slave cylinder line which may be preventing the fluid in the line from draining by gravity alone. Releasing the line pressure will also cause fluid to drain from the upper bleeder valve line. However, once you get the slave cylinder line filled with fluid, and no air, then you’ll have enough fluid pressure in the line to force new fluid back up and out of the upper line. No Pressure Building Up in Line – If there is a lot of air trapped in the line, it will be difficult to build pedal pressure. I think this is why it is suggested to use the gravity bleed procedure in order to establish one line filled with fluid between the master and the slave. After you have bled the bottom line, begin to bleed the topside valve. Do this a couple of times; and then go below and do the slave again. Keep going back and forth until you get some pedal pressure. It will come. Remember to Keep the Reservoir Topped Off – When air gets into the line at the reservoir, it must be completely bled through the whole length of the system. Keep a close watch on the fluid level in the reservoir. This is the single biggest problem novice mechanics encounter. They bleed and bleed, and cannot understand why the pressure does not build. Once air enters at the reservoir the system must be bled again, purging all the fluid in the system. This can be very confusing if you do not understand what has happened. Air in the Master Cylinder and Bench Bleeding - Some Forum Members swore they had to bench bleed a master cylinder in order to obtain pedal pressure and/or to fully bleed the system. Unless your master cylinder is new, I can not see why it would be necessary to perform this process. Most posts seem to think that even new cylinders can be bled in the car. Bench bleeding is just what it sounds like; bleeding the unit while it is out of the car, on the bench. Advocates of bench bleeding indicate they thought there were air pockets in the design of the master cylinder that could only be cleared by turning the unit so that the air would rise and escape. It is possible. I do not know. Large Bubbles in the Line - Large bubbles inside the clear plastic hose confirm that air is being evacuated from the system. Note that if an air pocket is introduced at the master cylinder; one must bleed out enough fluid to allow this air pocket to effectively travel the entire length of the tubing. Do not be fooled by seeing clear clean fluid in the plastic tubing. It is a good sign, but you cannot be certain that all the air is out of the line until you are certain you have moved enough fluid to purge the entire system. At least five or six full pedal movement bleeds with a pressurized pedal are required to be certain the whole length of the upper tube has been purged. Look for Changes in the Color of the Fluid - One way to tell if you are completely purging the old fluid from the length of the line is to observe a changed color of the fluid. As the bleeding is begun, one will first observe the old, darker-colored fluid. When the old fluid has been purged, one should observe a color change in the fluid, becoming much lighter and clearer. This observation is only valid when you first bleed the system, disposing of the old fluid. In order to observe this change in color you need to use a quality latex clear hose when bleeding. Small Foamy Bubbles – Determining the source of these small foamy bubbles is a tough call. Sometimes the foaming means you should to continue bleeding because these are large bubbles that have been agitated into smaller ones. They are coming from upstream in the piping and you need to continue to bleed them out. However; sometimes the line has been cleared of all upstream bubbles; and these foamy bubbles are a symptom that air is being drawn in around the threads of the bleeder valve at the very end of the line. Air Drawn In Through (and around) the Valve Threads – The bleeder valve screw-end, and its threaded hole it mates to, are pipe fittings. All pipe threads are tapered. As you unscrew the bleeder unit to open the valve, the valve backs out its tapered hole, and an air gap is created. During the bleeding process, foot pressure on the clutch pedal forces fluid through the bleeder valve orifice and out through the valve. This line pressure also creates a low pressure point at the air gap between the pipe threads. Air can [sometimes] get sucked into the line at this point, just before the valve. While this foam appears to be coming from far upstream; it is actually entering the system at the very end of the line. Use Teflon Tape to Prevent Foaming - To prevent foaming, wrap the bleeder valve body threads with a short length of Teflon tape. Be careful not to cover the orifice [hole] near the bottom of the valve. This passage must be kept clear in order for the fluid to properly exit the bleeder valve assembly. The Teflon tape fills the gap in the pipe threads and reduces the amount of air sucked in between the threads. Mity Vacs and other Suction Devices - I used a MityVac as an aid in bleeding. This is a vacuum assist device designed to evacuate fluid by sucking it from the exit side of the system. While my buddy provided line pressure on the pedal, I created a vacuum on the other end. Be cautioned that foamy bubbles are a common occurrence when using this device. (see above) Again, I used Teflon tape around the bleeder valve threads and it stopped most, but not all, of these tiny bubbles. I was not impressed by this device; however, I mention it because some Forum Members swear they could not bleed their system until they used one. Pumping the Pedal Fast or Slow? - There seems to be some disagreement about whether of not one should vigorously pump the pedal prior to bleeding. Some posts report they could not remove air pockets when pumping as one would do in a normal bleeding procedure. Then after becoming frustrated, they pump like crazy…and the air is purged. They say you need to pump as fast as you can for 15 to 20 pumps. Hold and bleed. Other posts suggest this action agitates the fluid, possibly causing a few large air bubbles to break down into many small bubbles or even to create more foaming. I do not know. A Leaking Slave Cylinder Will Suck In New Air - Initially pumping the pedal in a normal fashion helps to create pressure in the line. However, once a minimum line pressure is established, each pumping cycle also actuates the slave cylinder. Unlike bleeding a brake system, where you can pump up a very hard pedal; in a hydraulic clutch the slave cylinder piston will move. This limits the maximum line pressure. If the slave cylinder is leaking, pumping the pedal might also cause a hidden problem by introducing air at that point. If that happens, you must replace the unit before continuing the bleeding process. Erratic Low and High Pedals After Adjustment - After bleeding, and then setting the clutch adjustment screw/nut, I drove around for a dozen miles. I then noticed the pedal adjustment had changed. First the pedal was soft and low (near the floorboard). Then it went high and became solid or firm. My theory is that two events occurred. First there was some air trapped in the system that rose to the top line and caused the soft pedal. However, as the engine warmed, it heated the air in the line which then increased the pressure. The two effects counteracted each other, but not in a direct balance. Many posts report that they bled the clutch and had it adjusted, and then drove a couple of days. Then they found it necessary to repeat the procedure before the clutch was good to go. Adjusting the Clutch Pedal Thread Adjusting Rod – Many posts are available on this process. I would suggest that unless you have installed a new clutch or clutch part, do not adjust the screw until you are sure all the air is purged. As noted above, air can cause the pedal release point to rise and fall. Try to keep the variables limited. Change only one factor at a time and get all the air out first. Then adjust clutch pedal threaded rod. Other Notes:
• It does not matter whether the clutch reservoir cap is on or off.
• It does not matter if the bleeding tube end is submerged in fluid in a bottle, with all air removed from the tube. That requirement is for siphoning, not bleeding.
• It does not matter whether the engine is running, and/or the booster is actuated. Add Reservoir Capacity - One idea I got from this forum is to maintain fluid in the reservoir by using a funnel, or cylinder, stacked onto the master reservoir. Use some body filler putty to seal the seam between the two. Raising the walls of the master cylinder reservoir creates a larger reservoir which necessitates less refilling. Bleeding and Adjusting Clutch Reduced Transmission Grind - My transmission had one of the infamous grinds from first to second. I had this second gear crunch for a long time, and did the MT-90 fix which eliminated some of the crunch. I assumed I had a synchros problem. However, the grind was almost eliminated by properly bleeding and adjusting the clutch system. After the bleed, there was a noticeable improvement in gear shift smoothness that I can only attribute to a better clutch action. It should be noted that I raised the pedal release point when I adjusted the clutch. I think that doing this allows the clutch to more fully disengage sooner. I would have sworn the grind was strictly synchro, and that my clutch action and timing was fully disengaging the unit. However, after the clutch adjustment, I changed my opinion. However, now I think that before the adjustment, the clutch was dragging during disengagement. This little lag kept the main shaft spinning just enough to overwork the synchros and prevent a normally quick shift, and hence the grind. I still have a little grind, and I know this is a synchros problem. But between the clutch work and the MT-90, most of the original grind is gone. New transmissions are $2000. Changing over to Silicon Fluid – Courtesy of Tom B (IN)
“Whatever the [DOT] designation, I use silicone-based brake fluid in my clutch system. It will not let water form in the fluid, which means that the slave cylinder, at the lowest point in the system, won't rust out from water. It's also a bit thicker than regular brake fluid, so it will give you 'better' clutch action. The change-over means you have to run your current system completely dry, as the silicone-based stuff is not compatible with regular fluid. It's easier than you might think: silicone-based fluid is usually a different color. My suggestion is to do a gravity bleed: open the reservoir cap, then get under the car, put a pan down there, and remove the bleed screw completely. Go topside again, and pour silicone-based fluid into the reservoir as it drains down. MAKE SURE it doesn't go dry and get air bubbles in the system! When the fluid down below is flowing the right color, put the bleed screw back in, and tighten it down. Then, perform a normal bleed on the secondary bleed point in the engine bay - also until the right color fluid comes out. The whole process takes maybe an hour, and consumes less than a pint and a half of fluid.” Regarding the reason there is a top tube along the passenger fender- - Don Mendell (AliaZ) says the large diameter tube that leads up to the bleeder on the fender is there to dampen vibrations in the clutch pedal. Evidently brake fluid is slightly compressible The large diameter tube holds enough fluid to absorb any pressure fluctuations caused by the pressure plate on your clutch when the pedal is depressed. You can remove this tube...in theory, you may feel a little more feedback in the pedal, but I've heard it is hardly noticeable. I may do this while my motor is out. Clutch bleeding will be *much* easier without this hydraulic damper.
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The Ultimate Guide to Bleeding your Clutch (long) - 
