dgmattingley

Folks,

Searched for this but couldn't find the same problem.

While I had the tranny out for repair I replaced the clutch slave cylinder. Got everything buttoned up, when I bled the clutch slave I first rapidly got about 1/3 cup of fluid, but after that I heard a lot of air hissing. The bleeder lost pressure. Tried again, just air hissing and very little fluid, lost pressure again after a few seconds.

I checked and the clutch pedal is just going to the floor as if the system needs to be bled some more. I bled one of the brake calipers just to see and all is normal. There are no leaks at the hydraulic lines into the slave cylinder. Should I continue to try to bleed the slave cylinder, or does the air hissing indicate some other problem? The master cylinder is now between max and min.

Thanks for any advice!

AOW162435

Are you 103% certain that the slave rod is correctly engaged with the 'cup' of the throw out bearing arm? If not, the rod will slip right past the arm the first time pressure is applied.

You can check correct engagement with some monkey maneuvers under the car using a small mirror and looking into the inspection port on the left side of the bell housing.



Andreas

Mike J

Yeah, I have gotten this and have not figured it out yet...maybe someone can chime in. If I pressurize the reservoir, and its kept full so no air enters the system, I usually get large bubbles and air into the clutch system even on a simple bleed. The only way I figured out of it is to the someone in the car manually pumping the clutch while I was underneath the car (not too bad because of the lift), coordinating the pump with opening the bleed nipple, and keeping doing this until it clears, often with the reservoir being pressurized as well. Sometimes it will take over a litre of fluid before it gets air free.

Its almost like the system is picking up air somewhere...it has happened on a variety of 993's so its not just my car..... Bleeding the brakes is dead easy in comparison, but the clutch slave always seems to get air in it.

I pressurize the reservoir ala brake bleed, use a good hose on the bleed nipple so no air in introduced there, and bleed it...and get tons of air (as dgmattingley notes above). Very frustrating.

Who has experienced this?

Cheers,

Mike

Gunter

Had the same experience for my first slave cylinder bleed, very puzzling and frustrating but I found out why:

The reservoir on mine is combined brake and clutch slave........................at first I didn't fill enough fluid and got the same hissing of air coming from the pressure bleeder. Make sure you put enough fluid into the pressure bleeder and try again. It takes very little pressure, maybe 10-15 lbs.?

The reservoir may look full but it fools you because the compartment for the clutch has a small pipe stud inside you can't see and it takes only a small drop in fluid level before it sucks air.

With more fluid and no pumping the clutch master, the bleeding went just fine.

kjr914

^^^
+1 on Gunter.
The clutch slave portion of the brake fluid reservoir is a very small compartment towards the back of the car. Very easy to drain it because the rest of the fluid reservoir looks full, while this small section drops in fluid level. Once there's air in the clutch slave, the clutch pedal snaps right to the floor (disclaimer: on a C4S, YMMV).

Ask flatsixforme and I how we know...

jo-hans

same here

matt777

I just find it easier to bleed the slave using a vacuum gun with tubing and a plastic canister. I just build up vacuum with the hand pump and crack the bleed fitting. Repeat.

chris walrod

Yes, one has to keep the reservoir topped up all the way to the top, I mean all the way as the fluid pick up point is much higher in the reservoir than that of the brake circuit feed. This is a safety measure.

Mike J

Hmm, interesting, I will have to check out the level behind the baffle that is in the reservoir. I use compressed air pressure regulated down to 5-10psi, and a cap on the car's reservoir with a air nipple, so I do not use a pressure bleeder (i.e. secondary container).

Regardless, i never let the fluid level go below min, so I guess the problem is "which min". Looking from the front, the min would be for the partition for the brake, and I guess I do not see the clutch fluid level as clearly. Damn fluids and the opacity of the reservoir make it hard to see - I will use a backlight next time.

Thanks for the hint! It was not impossible to solve, I just pumped with a fuller reservoir, but never really dug into the core reason.

Cheers,

Mike

DanL993

This is a GREAT thread. I just bled the clutch, and maybe got lucky there with no problems. You guys and this forum are great.

I'm keeping this one on file. Thanks.

dgmattingley

Thanks for all the replies.

The brake fluid resevoir is half-filled at this point, so I'll refill per instructions from Chris and others and hopefully that does the trick, and hopefully it's not either a faulty new slave or that I didn't get it engaged properly with the clutch fork, because it sure would be a pain to have to pull the whole thing off again!
cheers,
Don

k722070

I tried a couple times to keep the reservoir filled to the top, but once you get air in the line there is not enough fluid in the reservoir(above the pick up point) to refill the line.
ended up using gunter's method of filling the pressure bleeder, kind of a hassle but it works.
once the air is out of the line, bleeding the slave the second year was easy and I didn't need to fill the pressure bleeder.

Gunter

In hindsight, I'm sure that with a lot of fluid in the pressure bleeder the job takes less than an hour without any air getting into the system.

Since the clutch reservoir looked full, and the pick-up stud impossible to see, a real panic ensued with thoughts of having to dismantle the MC etc.

After more than 1 liter went through using the standard pedal-pumping and me getting real p-off about the constant hiss of air, I realized that a pressure bleeder has to be used with lots of fluid to keep the clutch-portion of the reservoir topped up.

With separate reservoirs on some models, that problem doesn't exist. The designers at Porsche must have a devious sense of humor aimed at the old-school pedal-pumping brake-bleeding dudes.

dgmattingley

Wow am I glad I posted this here, I was about to take off the slave cylinder as my next troubleshooting step. Keeping the fluid topped up before any air got into clutch was the key. I agree with the post above, a devious system!

Here's what worked for me:
Fill up brake fluid resevoir to max
Pressure bleeder to 8-10psi
Bleed slave for about 8-12 seconds
Top off resevoir
Repeat above 3X
Clutch pedal is firm and all's well

JB 911

This a great thread. Because I found it, it means I'm in the rookie first year mistake camp. I was able to get the air out of mine keeping motive dry by using dgmattingly's technique above Probably took me about 5 cycles though and then did a couple more for good measure.

I'm undecided for next year though. What is a good amount of fluid to consider bleeding the system? This year I just did it for about 15- 20 seconds after it started coming clear.

It seems it might be easier to just fill up the bleeder and bleed away next year. To K722070 or anyone else who does annual bleed dry, how many cycles of filling reservoir do you do and/or how much fluid do you bleed total?