i have a hydraulic clutch system where the pedal feels spongy, doesn't return fully all the time, and even stays depressed when you take your foot off. when the pedal stays depressed the clutch is not disengaged (ie it is connected to the engine). I cannot gain access to the slave cylinder as it is inside the bellhousing and not visible, however the fluid level is good, it doesn't appear to be leaking any fluid, there is no sign of any fluid at the master cylinder, and I have bled the system quite thoroughly.

 

I'm seeking to diagnose whether this is the master or slave cylinder that is the issue - before I remove the gearbox or anything overly enthusiastic.

 

I was wondering if anyone has put a pressure gauge on the clutch master cylinder in place of the slave cylinder, then applied pressure and checked to see if it held.

 

While I was typing this, I've got to thinking - if the fluid level hasn't dropped in the reservoir, then it obviously isn't leaking externally, and if the slave cylinder had the problem, it would have to lose pressure externally. This would then imply that the fluid is leaking back to the reservoir from inside the master cylinder.

 

Thoughts and ideas?

 

Robert.

J series box or commodore?

Having just gone through this on the Mrs' mazda, its definitely your master cylinder bypassing.

 

If there is no leak around the slave, and you aren't losing fluid, its time to replace the master.

Having just gone through this on the Mrs' mazda, its definitely your master cylinder bypassing.

 

 

thats what i think too.

 

from my understanding fluid can get past the seal in the master cylidner, but just go back to the resevoir. not leak out.

 

i think i had this when my mastercylinder was on its way out in the ke70. clutch was doing strange things intermitently (kinda like you describe). i gave it a good bleed and it came good for a few days, then it failed on me.

 

is there an inspection hatch on the gearbox where you could see the clutch slave moving? (i assume you would have tried this if there was)

 

btw its nice to see a properly written tech question for a change....

try a simple clutch bleed?

 

so if your in gear and foot on the clutch. the clutch will slowly engage and you'll take off?

+1 for master, mine had similar symptoms on my hachi. Do the slave while you're at it, it'll go in the next 6 months anyway.

Can only be master cyl as either you'd lose fluid or the fluid wouldn't return to the reservoir and the clutch wouldn't push the thrust bearing back. ie rusted thrust carrier jamming it forward.

 

Even if the pedal was rusted and jamming the clutch wouldn't engage the gearbox while the pedal was stuck down.

 

You'd be right with the T-piece and a pressure gauge too. It would show the pressure dropping as the pressure plate returned and the pedal still stayed at the floor.

+1 for the seals in the MC. Should be able to get a seal kit for it. Or are they cheaper to fully replace the MC itself?

Have seen where the flexi line to the slave has collapsed in the inside, not very common but symptoms are the same.

 

Oh and give it a bleed before you pull anything apart.

Edited January 7, 201115 yr by TRD ke70