How do you test the clutch master an slave cylinder?

[nbeihl]

How do you know if you have a bad clutch master or slave cylinder if it is not leaking and the clutch pedal is not engaging or disengaging the clutch?

Also, can you bleed the clutch with negative pressure at the slave cylinder, or is it necessary to use positive pressure on the reservoir?

[JFP in PA]

As I have stated before, I have no love for vacuum bleeding systems, they invite too many problems. Positive pressure, like from a Motive bleeder, it the best approach. The clutch needs to be bled with the pedal held fully depressed to the floor, after which you will need to manually pull it up, and then it will function normally.

The clutch master rarely is a problem, we see many more slave problems, ranging from leaking to simply not working, often stopping suddenly. Fortunately, the slave is not that bad a DIY project.

Edited January 22, 2012 by JFP in PA

[nbeihl]

Pressure bleeder it is, thanks.

My clutch went from working perfectly to not working AT ALL. It did happen on the day of the first cold snap of the year. There is no leaking fluid which leads me to believe it is the master, slave, release lever, or pressure plate. I want to know for sure it is not the master or slave cylinder before I break into the clutch.

Is there a way to see if the slave cylinder is working by watching the actuation from under the car?

[JFP in PA]

No. If you look at a picture of the slave, its actuation arm/rod is inside the bell housing when it is installed, so you cannot see anything moving. It would be possible to pull the starter and insert a fiber optics cam to see it move, but I rather doubt you really want to get into that level of diagnostics.

You can pull the slave and operate it outside the bell housing on a bench using compressed air to see if moves correctly.

[mattatk]

Well my master cylinder failed, symptoms were the same as general clutch failing until I bled the clutch, well I couldn't bleed it (with pedal depressed & pressure bleeder attached, no fluid would flow). Replaced it & pulled old one apart, failed seals inside.

[nbeihl]

Well, it seems that without an actual leak, it is tough to diagnose a bad master or slave cylinder. Once I get a chance to take it apart I will try the compressed air trick. Thanks for the information.

Here is a link to a picture of the slave cylinder for refrence to JFP in PA's post.

http://www.pelicanparts.com/cgi-bin/smart/more_info.cgi?pn=997-116-237-02-M38&catalog_description=Clutch%20Slave%20Cylinder%2C%20Carrera%20%32%2F%34%20%28%31%39%39%39%2D%30%34%29%2C%20Each%20%20%20%20%20%20

Here is a link to the bleader mentioned above.

http://www.motiveproducts.com/