Bleeding the Clutch on a 996 4S

[19Fatboy53]

I have a 2003 CS4 which I just recently started having issues shifting gears, specifically into reveres or down shifting to first and second gear.

It feels as though I have plenty of clutch, so I decided to go into DIY Brake & Clutch fluid change and bleeding instructions in which I was able to bleed air out of the system.

However, now that I’ve bled all the air out of the system I cannot shift gears at all.

Can you guys help?

19Fatboy53

[JFP in PA]

Did you hold the clutch pedal to the floor while bleeding the slave cylinder?

[19Fatboy53]

Yes, I followed the DIY as posted. The pedal was held to the floor each time I tried bleeding the system. I blead the system four times and three of the four times air came out with the exception of the last when only fluid came out.

[JFP in PA]

You may have a dying slave cylinder, not totally uncommon. A realtively simple DIY project to replace, you may want to search the archives for write ups......

[nbeihl]

What are some of the symptoms of a slave cylinder failure. I was assuming that fluid loss or dripping on the ground around the transmission / clutch would be one of the main indications.

Can the slave cylinder fail without there being a leak?

The same indication should be true with a master slave cylinder except the leaking would be up front and you could perhaps have break issues since they share the same reservoir, right?

I am still learning this particular system on our cars.

[19Fatboy53]

I was thinking it might be the slave too in that it might be bleeding through, but, again, how would air enter the system with no visual signs of leaks?

Again, thanks for all your help/input in helping me to resolve this issue.

Fatboy

[JFP in PA]

When the slave fails, they sometimes leak internally. When this happens, insufficient hydraulic pressure is developed to operate the clutch, but there are no external signs of leakage. The slave simply no longer pushes hard enough to work the pressure plate and release the disc.

Edited January 4, 2012 by JFP in PA

[19Fatboy53]

JFP in PA,

I replaced the slave cylinder without any issues, but, now I am having a heck of a time trying to bleed the air out of the system eventhough I followed the instructions from DIY Brake & Clutch fluid change and bleeding instructions to the tee.

I even tried using a hand operated vaccum pump which seems to work since I can see the air bubbles coming out, but, I am having issues holding a vaccum on the system; probably leaking by the seals on the container so I am thinking of buying a new pump.

Oh yes, I was told that if I use a vaccum pump I don't have to hold down on the clutch pedal but need to ensure there is plenty of fluid in the brake mastercylinder, is this correct?

Please advise, and thanks for any inputs you may have.

19Fatboy53

[goldenwarrior1]

Holding down the clutch is only applicable to manually bleeding the system. With the pedal down, pressure is held against the system and forces out a small amount of fluid/air with each compression. Holding the bleed valve open too long or allowing the pedal to retreat will draw air into the system. If using a pressure bleeder you simply use the tool to maintain the pressure. Pressure bleeding is better as it provides a better flush of the system in short order. And you will need to keep an eye on the reservoir to ensure you don't suck huge amounts of air into the system and have to start over.

Edited January 12, 2012 by goldenwarrior1

[JFP in PA]

Holding down the clutch is only applicable to manually bleeding the system. With the pedal down, pressure is held against the system and forces out a small amount of fluid/air with each compression. Holding the bleed valve open too long or allowing the pedal to retreat will draw air into the system. If using a pressure bleeder you simply use the tool to maintain the pressure. Pressure bleeding is better as it provides a better flush of the system in short order. And you will need to keep an eye on the reservoir to ensure you don't suck huge amounts of air into the system and have to start over.

That is not completely correct; you still need to hold the pedal to the floor while using a pressure or vacuum bleeder. When you are finished, the pedal will stay down, and needs to be manually pulled up, after which it will function normally......

Edited January 12, 2012 by JFP in PA

[JFP in PA]

JFP in PA,

I replaced the slave cylinder without any issues, but, now I am having a heck of a time trying to bleed the air out of the system eventhough I followed the instructions from DIY Brake & Clutch fluid change and bleeding instructions to the tee.

I even tried using a hand operated vaccum pump which seems to work since I can see the air bubbles coming out, but, I am having issues holding a vaccum on the system; probably leaking by the seals on the container so I am thinking of buying a new pump.

Oh yes, I was told that if I use a vaccum pump I don't have to hold down on the clutch pedal but need to ensure there is plenty of fluid in the brake mastercylinder, is this correct?

Please advise, and thanks for any inputs you may have.

19Fatboy53

I have never been a fan of vacuum bleeding tools for a variety of reasons; get a pressure unit such as the one Motive Products makes.

[Loren]

I agree with JFP in PA - Motive or a similar pressure bleeding tool is the only way to go.

[19Fatboy53]

Guys,

I finally received my Motive Power bleeder but have one question; after going to the process of checking the bleeder for air leaks, there were none, I filled up the tank with brake fluid as directed, but, I notice that when I went to pump up the pressure it filled the clear line with fluid and “air” that traveled through the hose into the reservoir. Is this normal?

The reason I ask is that I am afraid to pump more air into the system defeating my objective, please advice thanks.

[JFP in PA]

You will be fine, the Motive unit needs to clear the air out of the line before the fluid flows, and this will just sit above the fluid level in the system reservoir during the bleeding session. It will not get into your system.

Small bit of advice for the future: I always suggest that people fully hook up the Motive unit dry (no fluid) if they do not use it regularly, then pump it up to about 10-12 PSIG and let it sit for about 10 min. to see if the pressure holds. If it does, you are golden and can release the pressure by unscrewing the pump cap on the Motive unit slightly until the pressure vents off, then fill the unit, pressurize and commence the flush. The reason I suggest this “dry pressure” run is that if the unit, the line or the cap it is connected to are leaking, you will find that and be able to fix it without brake fluid, which is Hell on paint, spraying all over the place. Better safe than sorry.

Edited January 19, 2012 by JFP in PA

[logray]

You will be fine, the Motive unit needs to clear the air out of the line before the fluid flows, and this will just sit above the fluid level in the system reservoir during the bleeding session. It will not get into your system....

+1 totally normal to see some air "behind the fluid" in the tube coming from the bleeder to the cap.

[19Fatboy53]

Guys,

I used the Motive power bleeder per your recommendation and everything seemed to work out accordingly, i.e., air came out in droves until finally nothing came out but clean fluid. However, I still can’t shift into reverse or 1st and 2nd gear and the pedal feels spongy and not at all like before.

My plan for today is to take the care off the ramps to see if the angle in which the car sits is causing the issue since the OEM recommends to take the left wheel off to bleed the slave…it doesn’t make sense but I am at wits end and pretty close to just having it towed to the dealer to get fixed, dang it all.

Any other suggestions would be greatly appreciated.

[JFP in PA]

The clutch slave is located in a tight spot, but is not much of an issue to bleed. Removing the rear wheel helps to see it, but really does not make it any easier to get at. Just be sure the clutch pedal is held to the floor (an adjustable hood prop or section of 2X4 seem to be the preferred tooling) the entire time you are bleeding the clutch. When you are done, the pedal will remain on the floor and must be pulled up manually, after which is should be fine.

If you have done a full bleed of the clutch hydraulic system (let it run for a bit, it hold ssome fluid volume) and it still feels funny, your clutch slave may be on its way out.

[Laurence Gibbs]

Bringing this back up. I realise the factory manual says depress the clutch when power bleeding but everytime I try this I get no flow ? If I leave the peddle up I get flow and can bleed . Can someone explain ? I have seen it mentioned that if the peddle is depressed it blocks the port and stops the flow and I have also seen it said (de Mort) that you depress the peddle ? Confusing. I have tried bleeding both with an original master cylinder and a replacement and neither bleed with a power bleeder with the clutch depressed.  What am I doing wrong ? 

[Loren]

Optional Clutch Bleeding
This is best done when you are bleeding the left (driver's side) rear wheel as the clutch bleed valve is mounted high above the axle on the transmission.

1. Push the clutch pedal in by hand (very slowly) and use a long piece of wood to hold the pedal down. I wedged the other end (of the wood) between the seat and door frame -- with plenty of soft padding to avoid scratches. A second option is to have a 2nd person sit in the car and keep the clutch pedal FULLY depressed.
2. Open the clutch bleeder valve until clear, bubble free brake fluid emerges (at least 30 seconds according to Porsche). Remove the wood. Then, pump the pedal again very slowly by hand for a further 60 seconds. After pressing the pedal down fully about 10 to 15 times, leave the pedal in its normal position. After allowing a fill time of 90 seconds, check that no more air bubbles appear at the bleeder valve (use a collecting bottle with a transparent hose). Then close the bleeder valve. Wipe off the area and replace the rubber protective cap over the bleed screw.
3. You may notice that the clutch pedal does not return... so carefully pull it up (slowly) to it's normal position. Then depress it (slowly) a few (at least 5) times. In a few cycles the feel should return.

[Laurence Gibbs]

Loren, if I do this I can't get past step 1 as no fluid will flow ? The only way to get fluid to flow is to bleed with the pedal up ? Is this something to do with how slowly you let the pedal down ? I can't see how that would make a difference , clearly you don't won't it to slam to the floor . But it's simply going from one end of the cylinder to another.  

[Loren]

Bad slave cylinder, bad bleed valve, clogged brake clutch line?

The car is likely 20 plus years old.

[Laurence Gibbs]

I have changed the slave which is what started it . So I changed it back ( the original slave  was fine when I changed it out as it was being done as part of clutch change) problem still persisted.  I then changed the master cylinder thinking maybe that might be it . No change and both master cylinders won't let me bleed the clutch with the pedal down . I have recently changed the flexible line to the slave along with the hard line back to mid way along the car. Will see how that goes . I am just real curious why I can't bleed with the pedal down . This has been over probably a couple of years now . I will bleed it , it lasts a few weeks , bleed again lasts a month , bleed again lasts six months etc . It's ruining my confidence in the car as when I do want to use it , pedal drops . I expect I will have to bite the bullet and go back through with another slave and possibly master cylinder if the new flexi / hard line does not help. There are no signs of leaks and the flexi was corroded but OK when removed. If I can find the old master cylinder I may have it apart and see just how it works for my own piece of mind . Thanks for the replies . 

[MontrealC4S]

FWIW, the Pelican DIY states specifically to NOT depress the clutch pedal when pressure bleeding...

[JFP in PA]

40 minutes ago, MontrealC4S said:

FWIW, the Pelican DIY states specifically to NOT depress the clutch pedal when pressure bleeding...

 

FWIW Pelican often offers incorrect advice along with their outrageous pricing and bogus substitute products.............

[Laurence Gibbs]

Unfortunately I can't post pictures here . I have a post on the 996 carrera owners Facebook group do a search there for pics.

I took the spare clutch master cylinder apart . It's a simple cylinder with a piston very similar to the slave in design. It has what I can best refer to without pictures as a bicycle pump seal . The type that is a wedge shape. Push the piston down the cylinder and the seal expands to seal the cylinder and push fluid at the outlet.  Now here is the interesting bit . The piston at full travel reaches a step in the cylinder that stops further movement forward . This leaves the seal sitting against the step in the cylinder . I am at a loss to understand how any further fluid can flow when the seal hits the stop as the seal is splayed out against the stop. Hopefully of you look at the pictures on the FB group you will get the idea more clearly. The inlet side of the master cylinder is part of the plastic body and fluid flows into the cylinder through a small port at the rear of the  cylinder all the time the piston returns back from the outlet and there is less pressure on the outlet than the in , fluid will flow past the seal and fill the cylinder . Aa the piston travels back down to the outlet the seal opens and will not let fluid past the seal.