Cloud964

Can anyone tell me what exactly is the function of a clutch slave cylinder, and what will happen if it's not working properly or fail ?
Also does anyone know the weight difference between an oem 16" wheel and a 17" ?

Drew_K

This may be simpler than the answer you're looking for, but the clutch slave cylinder is part of the hydraulic system that actuates the clutch disc. Thus, pressing the clutch pedal disengages the clutch disc, which disengages the transmission from the engine and allows you to change gears.

If the slave cylinder fails, presumably pressing the clutch pedal will not provide sufficient hydraulic pressure to disengage the clutch disc. This would make it difficult if not impossible to change gears without forcibly removing the gearshift from the current gear, and then having to rev match to put the gearshift into the next desired gear. Basically, it would be like changing gears without using the clutch pedal.

Are you having symptoms? If the clutch pedal isn't returning all the way, this can often be fixed by lubing the pedal assembly and bleeding the fluid from the slave cylinder.

As far as weight differences between OEM wheels, it depends on the type of OEM wheels. I have a set of 17 inch 993 wheels and 17 inch 996 wheels, and the 993's are MUCH lighter than the 996's. Typically, a 16 inch will weight less than a 17 inch.

Drew
92 C2

Dave R.

To amplify on Drew's comments a little:

The clutch master and slave cylinders are like syringes; push the plunger in and fluid comes out the end, force fluid into the end and the plunger comes out. The plunger of the master cylinder is connected to your clutch pedal, the plunger of the slave cylinder is connected to a lever in the clutch, and a hydraulic line connects the ends of the master and slave cylinders. When you push the clutch pedal, it pushes on the plunger of the nearby master cylinder, which forces fluid out of the master cylinder, through the line and into the slave cylinder, pushing the plunger of the slave cylinder out (and thereby the clutch lever) to disengage the clutch.

As to failure, some symptoms of a failing slave cylinder apparently include a "notchy" feel to the clutch pedal, as though something is binding, and the notchy feel gets worse as the car warms up. There are some threads about this over on the 993 forum, here are a few: <a href="http://forums.rennlist.com/forums/ultimatebb.php?ubb=get_topic;f=3;t=004842#000001" target="_blank">thread1</a> , <a href="http://forums.rennlist.com/cgi-bin/rennforums/ultimatebb.cgi?ubb=get_topic;f=3;t=000472" target="_blank">thread2</a>

Apparently some guys were seeing this as early as 50K miles. My car (a 1990 with about 45K) has these symptoms and I plan to replace the slave cylinder soon.

If there is a lot of play in the clutch pedal you might check this <a href="http://forums.rennlist.com/cgi-bin/rennforums/ultimatebb.cgi?ubb=get_topic;f=4;t=000078" target="_blank">thread</a> regarding the roll pin in the linkage assembly between the clutch pedal and the master cylinder.

Roygarth

Dave R

So a 'heavy' clutch does not necessarily mean I need a new clutch? Mines done 56K miles and I don't know if it's on original clutch. Garage says as it's heavy and I need new clutch. It definately feels notchy and the 'bite point' seems to vary with oil temp. I don't know if it's heavy as it's the ojnly one I drive! Plus it hangs a tiny bit?? Could it just be slave cylinder? How can one tell?

Thanks in advance
Piers
1990 C4 Coupe

Adrian

Dear Piers,
This is one of these situations where there is no black and white answer. My experience is that if the problem changes with engine temp that it is normally the clutch assembly not the slave cylinder. A faulty slave cylinder leaks and this happens all the time.
The only way you can convince yourself is to replace your slave cylinder. I would recommend you bleed the clutch circuit first. However I have to be honest and say that I think your clutch assembly is most likely the problem not the actuating system.
Ciao,
Adrian
911C4

Dave R.

Two more threads re the clutch slave cylinder, perhaps somewhat more helpful than the first couple threads.

<a href="http://forums.rennlist.com/cgi-bin/rennforums/ultimatebb.cgi?ubb=get_topic;f=3;t=006782" target="_blank">thread1</a> , <a href="http://forums.rennlist.com/cgi-bin/rennforums/ultimatebb.cgi?ubb=get_topic;f=3;t=006849" target="_blank">thread2</a>

964s apparently have the same clutch slave cylinder as the 993s. Or at least, if one buys a replacement the part will be the same as would go into a 993.

Flying Finn

How about squeaking sound when I press or depress the clutch?

I flushed the system, and it was gone for about a day and then came back... Otherwise, clutch seems quite ok.

Adrian

Dear FF,
I think squeaking would be a component up front. I would be checking thwe mechanicals of the pedal assembly and the master cylinder.
Ciao,
Adrian
911C4

Randall G.

Hey FF,

If you pull on one of the threads linked above, you'll read that my slave cylinder has been squeaking for over 6 years. It's a squeak (or stretching sound) when you operate the pedal at normal speed, discrete clicks when you operate the pedal very slowly. I can only hear the noise with the engine off and the door open. Pedal feels fine, no notchiness. A squeaky slave cylinder--without a notchy pedal--is common.

shaker71

My clutch pedal effort was high and the engagement point varied with temperature. I replaced the clutch master and slave and bled the system and the clutch is lighter, smoother and doesn't vary with temperature. It's a lot cheaper to replace these parts than a clutch; if you're not sure.

Jeff Curtis

FWIW, MY clutch squeeks, clicks and sometimes does not return all the way up.

BUT, when I push the pedal on the RIGHT, the car SURGES!! <img border="0" alt="[burnout]" title="" src="graemlins/burnout.gif" />

You will find that a lot of these issues can be eliminated by changing out the bushings in the pedal assembly...a task I have yet to take on in my 964, but performed on two previous 911s with great success. Another thing that a lot of people aren't taking into consideration is when they bleed their brakes, the same pressurized system runs your clutch master and slave cylinder, with the bleed screw being located at the slave cylinder, of course.

I have a local friend who owns a '93 964 who has changed out the pedal bushings, bled the system and still has the problem with the clutch pedal not returning all the way to default...I have yet to check it out in his car...need to get mine straight first!!

I doubt that a SLAVE cylinder is causing any squeeking at all, but if you are in fact hearing the noise from the bellhousing area, then I would NOT be concerned with the slave cylinder itself, but the fact that a metal rod protrudes from the slave cylinder and pushes on your release fork.

There are a few "metal to metal" contacts in the assembly, but it's not much to be concerned about if there is a dab of the proper grease in each area. Wurth now makes a VERY stick grease that our local shop uses, I'm trying it out tonight...when I mate my trans. back to the engine for install.

My best advice on these matters is to bleed the system FIRST, if problems persist, have the condition of your pedal bushings/springs and the clips associated checked out. If you have issues from there, it's possible you might have a faulty master or slave cylinder, but it's fairly unlikely.

Good luck troubleshooting!! ...I have yet to track my little "issues" down. <img border="0" alt="[grrrrrrr]" title="" src="graemlins/cussing.gif" />