Said M/C was replaced this week due to some small amount of leakage. Now
there is too much dead travel before the clutch is actuated. Shop is competent
(I have reason to believe...) but stumped. Bled it up the ying yang. At the
slave cylinder, by pressure to the reservoir... Problem persists??
Shop is not competent. Sorry. Park the car nose up and leaning to the drivers side as much as is possible. Jack the front right if you have to. Then go find the blue hose that is routed down from the brake master cylinder to the clutch master. Use tie wraps if you have to or remove it from the master cylinder and plug it with your thumb while you shorten it so it just goes around the side of the brake vacuum booster....Wait you probably don't have one of those. The goal is to have the blue hose going subtly down hill the whole way to the master cylinder input fitting. Use a mirror and a flashlight to see how you are doing. Once you have this tied up and sloping properly you can bleed again. If you do not get the loop that goes below the port out of the system you will never get the bubble out of the top of the master cylinder. What I am getting at is that it is a water level and gravity thing. Air rises to the top of the master and no matter what technique you use to bleed it don't move enough fluid to flush say 2" vertically of air. You could bleed til the 50th anniversary party with no luck.
It will work if you get it set up correctly. The other thing you have to do is make sure that the shop did not over adjust the pushrod at the pedal to make up for the bad bleed job. If it is over adjusted in too much then the port will not open and no fluid will flow down from the reservoir between applications. This is key to moving fluid through the system and to make sure that the clutch fully engages to soak up all that horsepower you bought (jealous).
If all that don't work you either have a problem with hydraulics or it is
just being a bitch. If it is being a bitch the last resort that I have used
successfully is to "burp" the clutch master cylinder from the pedal
This requires right angle snap ring pliers and it normally ends in a strained neck and lower back but it works every time without fail. Remove the pedal pushrod, boot and snapring from the front of the CMC and then with your finger or the pushrod push in and out on the piston till the internal spring pops it out flush with the end of the casting. Then with a little bouncing finger pressure it will start to pop out. Do this until you get bubbles at the top of the bore. You don't actually remove it but you do tip it so just the top of the seal comes out in the air. Then pop it back in after the bubbles turn to clear blue fluid. Only a drop or two comes out.
Put it all back together and no play at all.
Some are going to suggest that you remove the slave and push in on the
pushrod. That is a bitch but it might work. If you have a big loop in the
blue hose nothing will work except the burp. If you get rid of the loop anything will work.
Now go fix it and I will inspect your work personally in a few days. I think an extended quality check will be necessary. Very many nuances in the adjustment. Will have to cycle the clutch through all the gears many, many, many times to make sure.
OK, here goes.
MC Bleed: Bleed the master cylinder from......INSIDE the car (A trick Kempf told me about that works). Get yourself a good circlip remover.
Use a good pressure bleeder (I known 928 Spec. caries them, probably 928 Intl. as well). Remove the push rod from the clutch pedal. Pull back bellows cover. Remove circlip. When you see fluid start to seep out...PUSH THE CYLINDER BACK IN... :-)...It's all bled.
Now, for adjusting the clutch, remove the clutch housing cover and go in and just adjust the T's all the way out. Don't worry about getting them exactly to spec. in the service manuals. This will clear your clutch for proper operation and they will adjust them selves a bit anyway. See:
http://members.rennlist.com/jeifert/DD-CLUTCH-REP.html (not dial-up friendly). This briefly walks you through my clutch replacement where everything that could be a problem was.
Drop me a line if you have any questions. It's been a couple years since I've done it, but what I can't tell you I can probably steer you to someone else who can.
Servicing the Clutch Master is probably the most difficult job on the car.
The last time I had the job done. No way I wanted to attack it and I do everything else on the car. The guy doing the job took two days and a lot of swearing. It was worth every penny of the $300 the job cost.
The clutch master can be rebuilt from inside the car. This is probably the most cost effective solution to your problem. However, for a trouble free job you should replace the blue hose and the flex hose under the car going to the slave. That is if they are not so recent. These are the common points of failure.
For the best access to the Clutch Master the easiest approach is to remove the brake master and the booster. This will give you clear access. It sounds like a bit of work, but given the tight access problems, the extra work will make the job much easier. In addition, by removing the brake master you will have a chance to inspect it to see if it is bleeding fluid back into the booster - another common problem with the 928.
Removing the booster is a bit of a trick. The actuator rod has to be locked into the booster to get clearance.
Dan the Pod Guy
My empirical try did not give me a soft pedal. Just felt like there was more
bleeding to go, each master reservoir, like Joe, seeming to add less improvement.
It was like a couple of runs shook things up enough that any residue of air in
the master cylinder moved out and back into the reservoir.
So now my pedal is hard and OK.
As for master cylinder pushrod adjust procedure, I will scan the page of the workshop manual and e-mail you it direct, since I don't know if the list has a size restriction on replies.
As for crush washers, my local motorcycle shop has them, my local Porsche dealer was fairly competitive and my local fastener shop has them in their little bins.
Hope it helps.
Joe, Jay Kempf replied to my "lazy" pedal with:
The mysterious pumping the pedal fixes the clutch bleed is a short term thing. You still have air or the bleed screw is loose if that is what you are seeing. I have and several others I have talked to have had damaged bleed screws that caused less than firm pedals randomly.
Also, bleeding incompletely before adjusting the pedal pushrod can cause trouble as the clutch will sort of work itself in and come up the last little bit with use and then the pedal will be stuck slightly on thereby holding the clutch on.
So the morale is if you want to use either early or late spec adjustment the difference being slight play vs. preload you have to make absolutely sure that you have the clutch completely bled and settled before making the final adjustment.
Routing of the blue hose to get rid of the large air pocket is a good thing and takes a ton of consternation out of getting the air out of the top of the system.
I personally adjust my clutch right at the end of the clearance in the pedal pushrod without any preload. Cold days it has a tiny bit of play that goes away as the car warms up. Warm days it is right on. But I never let it get overly tight at rest. I also run very little spring preload and feel that I have better feel that way but it makes for a strong quadrocept on that side. Not a problem for a skier.