Recently replaced the clutch on my new C4. Though getting the transmission (4+3) back in gave me some headaches, everything went fairly smoothly and worked great the past few weeks since the job has been done. The only thing I noticed while driving was on very few occasions, the car would fight me a little going into first. I saw that the clutch fluid in the master cylinder was a little low and extremely dark and dirty. Noticed this about the brakes as well, so I figured I'd bleed both of these fluids and get some new fluid through the lines.

Bleeding the brakes went great, and all 4 calipers now have clear DOT 3 fluid running through them when bled. I went to bleed the clutch, which started out fine. I had someone else press in the clutch, then I'd open the bleeder on the slave, close the bleeder, then have them let go of the clutch. Did this multiple times with no issues and no air in the lines, just dirty fluid. After refilling the master cylinder a time or two, I got carried away and let the master cylinder empty, allowing air into the line. I refilled it with fluid and tried the same method to bleed. I got the old fluid bled out (the fluid in the line before I let air in), but after that was all gone, nothing was coming out anymore. By this point the clutch has little to no pressure, and the slave piston barely moves a centimeter when the clutch is depressed. I have the slave unbolted from the bell housing and at a 45 degree angle. I tried getting a vacuum bleeder and pumping from the slave bleeder, but still no luck. One thing I do notice is that when I push in the slave piston manually, the level of fluid in the master will rise. I've tried the conventional two person method, as well as using the vacuum bleeder method multiple times, but the clutch still has no pressure and the slave doesn't move. The master cylinder fluid level does not drop at all through any of these bleed attempts. It stays at a constant level the whole time. Yesterday I got the slave to move slightly more by pressing in the slave piston manually, having someone else depress the clutch, and then opening the bleeder. A few air bubbles came out, but if I went to bleed again, as soon as I open the bleeder valve, it only wants to suck in air/liquid. I have tried pumping the clutch pedal a bunch, have tried pumping then holding the pedal for a few minutes and letting it spring back up, but still no luck. Both the master and slave were working perfectly fine beforehand, and I see no signs of leakage, so I want to say that those aren't the issue. Note that the back of the car is jacked up very slightly lower than the front, only by an inch or two.

I would sincerely appreciate if anyone could help me get this clutch system working again. What was supposed to be a half a day job has now turned into 4+ days of trying to bleed. Thank you.

 

Update: I'm not the smartest. The rubber seal/cover that goes on the cap to seal the master cylinder fell into the cylinder without me noticing. The whole time I was trying to bleed I was sucking on that cover. Fluid is now bleeding out of the slave, albeit with a lot of air. One question I still have - If I compress the slave piston from underneath, then have someone press the clutch, the piston extends, but the pedal is extremely light with no resistance. If you try to pump the clutch a second time, there is no movement, as the piston of the slave is at its max extension, against the cylinder wall. I have to manually compress the slave to allow for clutch travel again. Is this normal? Is the lack of feel of the clutch due to the fact that it is not pushing against the fork? Or is there still that much air in the line causing this feel? Thanks

 

From your description, the master/slave combo is "very light" when not pushing the clutch fork---NORMAL--until at at the end of slave stroke, then solid
Suggest that has seemed to always work in the past
Remove slave cylinder from vehicle and then bleed the system, with the bleeder screw at the highest position possible. With the slave cylinder extended--the fluid is being pushed out and the clutch will feel "solid" like a brake pedal when properly bleed and bleeder screw closed.
No movement of the slave cylinder and 100% fluid, which cannot compress = solid feel to clutch pedal.
To install slave cylinder, crack the bleeder screw to retract the cylinder enough to bolt in place, tighten bleeder screw.
Then re-bleed should be "zero to no air" in system.
Clutch should disengage properly.

If clutch does no disengage, check travel of slave cylinder--should almost extend to maximum point
If no travel or minimal travel--suspect master or slave leaking internal/external.

 

I've changed three clutch masters on my 86 in the last five years. What works for me is to pump the pedal four or five times rapidly and hold for a second, then release as quick as possible. Do this three or four times. I then find a rod of proper length to run between the clutch pedal and the driver's seat. I depress the clutch pedal and wedge the rod between the seat and the pedal to keep the pedal on the floor then leave it overnight. In the morning I have a good clutch again.
These rebuilt parts are getting to be junk. We C4 owners are going to have to find another option for clutch master cylinders soon.

 

mine was always a pain to bleed. in the end i placed the slave in a position where the bleeder was highest, globbed the blled threads with grease, ran a clear vinyl tubing from bleed nipple to master reservoir, and kept pumping.

circulated fluid until all air out. found tapping the whole system helped get air that was clinging to insides out.

 

Too much work.



This works. PUMP THE PEDAL. You don't have to do full strokes and you don't need to hold the pedal down all night. All you need to do is move the fluid/air back and forth in the system...and cover/uncover the replenishing port in the master cylinder...that takes about 1" of clutch pedal travel to accomplish. I find the fastest/easiest way is to open the driver's door, and squat down by the rocker rail, reach into the car w/my right hand and just tap the clutch pedal down about...maybe an inch? or so? I Occasionally I'll throw in 1 full pedal stroke. Why use my hand? Easier and faster than with my foot. I can tap that pedal pretty fast with my hand/fingers. I've gone from a completely empty system, to fully bled, awesome pedal, in about 2 minutes or so.

 

fwiw, in my case, i swear on my life i pumped the pedal more than 1000 times. i never could get it fully cleared of air. not sure why. to be honest there was probably somewhere letting air in.

 

might also just be a junk master - I went through 3 crappy chinese masters in a little over a year on mine until I finally bought a Luk (which cost more than the 3 chinese ones put together!). Its still going strong a year and a half later at least. I never had too much trouble bleeding mine.

 

Bled a couple more times with the vacuum bleeder and bolted it back up to the tranny. Pedal felt great right away, shifts extremely smoothly. Have a much better feel for the clutch. Would old, dirty fluid have made that much of a difference in clutch feel? Or was there probably air in the line beforehand? Either way, runs great now. Thanks for the tips.

 

I don't know why this works.
I don't care why this works.
But I know this works.
Pump the pedal 10 times and hold it down for 30 seconds. Release the pedal by sliding your foot off it to the side, allowing it to spring up.
Do this a few times..
It works!

 

It worked b/c:
1. You barely had any air in the system and it was near the top (hence "10 pumps")
2. Air wants to rise to the top. This method is called "back bleeding" and is a very common procedure on small hyd systems such as dirt bike and snowmobile brakes, mtn bike brakes and so on.

If the system had more air in it, it would take a lot more pumps. See post #6.