Clutch Slave Cylinder Refuses to Bleed

Rodrigues · Feb 23, 2014

My clutch pedal has been feeling like there has been some air in the lines and while bleeding them I can't get the clutch master cylinder to draw any fluid from the reservoir. I unhooked the line from the slave cylinder and put it directly to a mityvac and it holds vacuum (as opposed to displacing the vacuum with brake fluid from the reservoir). I tried moving the pedal up and down (I have to manually pull up the pedal) and that doesn't do anything. Is there a reason why a master cylinder won't draw fluid from the reservoir? I tried reverse bleeding by pushing fluid from the slave cylinder into the master and it just pressurizes and doesn't actually flow any fluid into the master. It seems like no fluid will go in/out of the master cylinder and it's completely blocked.

jasonTDI · Feb 23, 2014

Since you don't include pertinent information such as the year and chassis of the car I'll make a couple points.

VW's don't self fill easily. They definitely don't fill under vacuum.(especially MK5) You need a top side pressure fill. If its a MK4 you have a bad master. (likely) if you have a MK5 you need a pressure fill on the reservoir and COULD have a bad master.

Rodrigues · Feb 23, 2014

It's a 2001 Jetta

jasonTDI · Feb 23, 2014

You can try pressure bleeding from the top but it's likely a bad master. Classic symptom when the pedal sticks to the floor.

Rodrigues · Feb 24, 2014

New clutch master cylinder fixed it. It bled right away when it was replaced!

The strange thing is that I actually drove in to the garage with the old master but when I introduced air into the lines it absolutely refused to bleed. I think the cylinder itself was probably fine but something inside the cylinder was blocking the fresh fluid from being able to enter it.

jasonTDI · Feb 25, 2014

There is a reason I said you need a top brake res bleeder.

Rodrigues · Feb 25, 2014

Air was introduced when I changed the transmission. The problem was the master cylinder and everything works now. The old master cylinder was bad because it was blocking brake fluid from entering it.

jasonTDI said:
There is a reason I said you need a top brake res bleeder.

jimbote · Feb 25, 2014

jasonTDI said:
There is a reason I said you need a top brake res bleeder.

I've bled dozens and dozens of dry vw mkiv and mkv clutch systems and never needed a top bleeder...the ones with a plastic bleeder screw do require unscrewing at least two full turns but the steel screw slaves only require cracking...I'm only using a mityvac and by the time the fluid gurgles into the cup the clutch is bled

Rodrigues · Feb 25, 2014

It also seems that any remaining amount of air anywhere in the system seems to bleed itself naturally over the next day or so.

jimbote said:
I've bled dozens and dozens of dry vw mkiv and mkv clutch systems and never needed a top bleeder...the ones with a plastic bleeder screw do require unscrewing at least two full turns but the steel screw slaves only require cracking...I'm only using a mityvac and by the time the fluid gurgles into the cup the clutch is bled

dunerking · Feb 26, 2014

I just swapped out my leaky slave cylinder on my 04 jetta,and Mityvac bleed it. But it's strange on my way to work in the morning clutch and gear ingaugment is fine,but same drive home 10 hours later and gear ingaugment on 4th and 5th gets difficult. Once I pump the clutch a few times I can get a smoother gear ingaugement. I've rebleed with same results. Any ideas? It's nice not having brake fluid on my driveway,but now have this procedure is disappointing. Thanks for any help!

dunerking · Mar 3, 2014

Bump it up,any suggestions? Thanks

CoolAirVw · Mar 4, 2014

this is why some mechanics might suggest replacing master and slave together.

You either have a leak or your master is bad.

dunerking · Mar 4, 2014

First I've heard of swapping out both at the same time. I guess I can throw a master cylinder at it. But why would it feel fine on my drive into work,but then feel different on the way home? Thanks for the info!

dunerking · Mar 7, 2014

Bump up,still looking for answers. Thanks

CoolAirVw · Mar 7, 2014

CoolAirVw said:
You either have a leak or your master is bad.

I suppose it wouldn't hurt to make sure the slave rod is set into the fork correctly.

dunerking · Mar 8, 2014

Well driving home yesterday the clutch pedal stayed down on the floor. Coast over to side of road,look under the hood and see brake fluid all over the place. Pull clutch pedal up and push in and fluid squirts all over,slave cylinder body has a crack in it near supply line! Lucky for AAA plus 100 mile tow. Just replace slave 3 weeks ago,time to call vendor and see what they say.

dunerking · Mar 18, 2014

Got my new slave cylinder and going to R&R hopefully tomorrow. It came with a new O-ring and a rubber grommet. I know the O-ring goes on the hydraulic input line,but where does the rubber grommet go. I don't see it in the Bentley manual. Thanks

CoolAirVw · Mar 19, 2014

picture?

dunerking · Mar 19, 2014

Pm sent

dunerking · Mar 19, 2014

Won't let me post attachments,I sent u my cell phone and I can text u a pic. Thanks.

CoolAirVw · Mar 20, 2014

The rubber thing that you sent me a pic of looks like the bleeder cap.

You just push it on the bleeder after you finish bleeding.

dunerking · Mar 20, 2014

Like a dust cap? I kind of thought the same,but the hole goes all the way thru. Thanks for the help.

dunerking · Mar 20, 2014

Just wanted to make sure it doesn't go inside something.

CoolAirVw · Mar 21, 2014

maybe its not the bleeder cap if it has a hole all the way through.

Heres the pic he sent me. Anyone else have an idea?

dunerking · Mar 21, 2014

Thanks Coolairvw! I was going to look at my Bentley manual and check if it's for a 6 speed Trans.

jimbote · Mar 21, 2014

Ha!....yeah...the thing pictured is the rubber seal that goes on the clutch line plastic adapter at the master cylinder end...if it's not on there you will never get it to bleed....sometimes they fall off or hang inside the master cylinder when removing the line....

CoolAirVw · Mar 21, 2014

Strange that they would send the master cyl seal with the slave cylinder. I don't think the original poster would have removed the line from the master to change the slave.

jimbote · Mar 22, 2014

that is strange ... i went back and reread and realize now that's a new seal ... i thought it was a mystery shop floor part

dunerking · Mar 22, 2014

CoolAirVw said:
Strange that they would send the master cyl seal with the slave cylinder. I don't think the original poster would have removed the line from the master to change the slave.

Thanks u guys! I only removed the hyd line at the slave cylinder,so I installed the new o-ring. I guess I'll save the other seal in case I swap out a new master cylinder. Now I can go ahead and finish this job and bleed the slave. Thanks for the help.

dunerking · Mar 23, 2014

Thanks for putting up with my dumb questions! Finished up bleeding and took it for a spin. Clutch action is feeling better than ever! Thanks again!

Clutch Slave Cylinder Refuses to Bleed

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