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Old 02-23-2004, 10:11 AM   #1
AcquaCow
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Default Best way to clean/rebuild a slave cylinder?

I had this lovely problem of my clutch pedal sticking to the floor, all due to a dirty, sticky slave cylinder. I took the boot off of it and was presented with a good bit of dirty, sticky, what used to be grease.

I cleaned that out and hit it with 3n1 oil & WD-40 to find that everything works perfectly, but I could only clean as far as I could push the piston back.

Is there a propper way to remove that piston to clean around it?

I don't think I need a new slave clyinder, but if that is the problem, I suppose I could replace it if need be.

Ideas?
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Old 02-24-2004, 10:50 PM   #2
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no love?
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Old 02-24-2004, 11:17 PM   #3
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The FSM seems to list as an R&R item....get a new one, I guess.
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Old 02-24-2004, 11:19 PM   #4
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hrm...oh well...

I'll just give it a good cleaning for now and then if it acts up again then I will replace it.

Parts are cheap.
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Old 02-25-2004, 01:09 AM   #5
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Grease the piston I guess is the only real remidy....
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Old 02-26-2004, 06:07 AM   #6
Charlie-III
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You should be able to just pop the piston out. Then wash all the internals with clean brake fluid, wipe dry and push the piston back in.

Bleed the system when done. BTW, it helps to have 2 people do this.
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Old 02-26-2004, 09:41 AM   #7
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The fluid up behind the piston was rather black instead of the lovely clear I poured in after I bled the system.

I think I need to bleed the whole thing out some day soon.

I took it all apart yesterday, wiped it down and cleaned it with WD-40 and lubed it up with a light spray of lithium grease.

It's been perfect so far today, but I think I need to hunt down some teflon spray and flush the entire system.

Any dangers when unbolting the slave cylinder from the hydraulic line attached to it?
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Old 02-26-2004, 09:44 AM   #8
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not really. Just be sure to bleed it about twice as much as you think you need to.

If you need some help come on out...the garage is great!
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Old 02-26-2004, 01:07 PM   #9
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It's actually still sticking a tad at high rpm's or when suddenly clutching in and blipping the throttle to downshift.

Wonder what is next to be cleaned?

New fluid should dissolve any old gunk in there right? It dissolves just about everything else...
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Old 02-28-2004, 11:34 AM   #10
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I'd rebuild it: a slave in good shape shouldn't have gunk inside the rubber boot, and there should not have been any lube inside that boot. The usual way a clutch slave fails is the rubber seal around the piston wears out and starts leaking fluid past the piston into the rubber boot.
Hopefully, there should be a clutch slave "major" rebuild kit available for $10-20, which will contain a new rubber boot, a new piston w/rubber seal, new internal spring, etc. Disassemble the original slave, noting how the parts fit together; once it's apart, really clean out the bore well, and make sure there aren't any scratches/gouges in the walls of the bore. Lube the rubber seal on the new piston with brake fluid only (many standard "lubes" will break down the rubber over time), install the parts, put the slave back in place, bleed/flush thoroughly, and you should be set to go.
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Old 03-01-2004, 09:56 AM   #11
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perhaps I'll replace the whole assembly...
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Old 03-06-2004, 04:36 PM   #12
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A hydraulic clutch (as with any other system that uses hydraulic/brake fluid) should NEVER have any other type of fluid/lube in it.
They can react to the seals causing them to fail or swell and bind.

I have found that part of the "it gets hot and the clutch quits working" is due to the aluminum piston and cast iron housing causing a bind due to different expansion rates when hot.

A lot of people have just replaced the clutch slave cylinder to resolve the problem, but I am working on a SS piston to cure the issue.
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Old 03-08-2004, 01:42 PM   #13
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Yeah...cleaning it out didn't do anything except keep it from actually sticking to the floor at idle...

I'll order a new one and see if that cures it.

It works great when cold though...gets slow when hot as you said...

Below 3k it's great, but once I get over 4krpm it actually sticks to the floor for a full sec.

If I take the rpm's up to 5k and higher, even sitting at idle in a parking lot with the E-brake on and in neutral... the pedal will stay to the floor until I let the rpm's drop below 5k.

Dunno if that is a slave cylinder issue or other...

I do know that if I pull the rubber boot and pin off of the slave cylinder and push the inside cylinder all the way down, it doesn't return to it's normal position very quickly...it can take up to a full minute for it to slide all the way back up.

It didn't do this on my friend's 2.5 GT wagon...

Ideas?

Last edited by AcquaCow; 03-08-2004 at 01:49 PM.
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Old 03-10-2004, 12:49 PM   #14
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There is a spring inside the cylinder itself.
Over time it either breaks or loses tension which can make it "stick" or react "slow".

I have found that the aluminum piston tends to expand faster than the cast iron body and the clearances go to zero.

The anti stick coating on the piston tends to wear as well.

When I get the chance, I will be making some SS pistons to fix this.
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Old 03-10-2004, 04:18 PM   #15
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let me know how this goes. I may be interested.

I am probably suffering from both.
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Old 03-11-2004, 10:25 AM   #16
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I have a subaru tech/friend of mine also looking into this problem, yesterday he PM'd me saying that subaru has an updated slave clyinder out that solves this problem. I'll get you the part # as soon as he PM's it to me.
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Old 03-20-2004, 11:24 AM   #17
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He didn't have the #, but I went ahead anyways and ordered from subaruparts.com. They have the updated slave clyinder.

Parts came in yesterday and the new slave cylinder is awesome. The noticable differences (visually) are the big crazy spring behind the piston, and a re-designed rubber seal behind it. The new spring is 2x the diameter and length of the spring in the old slave cylinder.

Unfortunately, with this installed, my clutch pedal is still sticking. This leaves only the pressure plate to be changed at this point. The one I got was stupposed to be an upgrade to the stock, but it is infact lighter than stock and not stong enough to push the throw out bearing back at signifigant rpm...but as you'll see in the vid below ~4mb it even sticks at idle.

This is my friend shawn trying to learn stick in the driver's seat, with me recording.
http://pimptastic.org/~acquacow/clutch/clutch.stuck.mpg

He was complaining about it sticking, so I broke out the camera and we tried to get it on video. It's not as good as the first time it happened to him though. We obviously counted down and anticipated this one... (you'll notice the tach at idle).
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Old 05-23-2004, 11:40 AM   #18
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Alright, everything is fixed now.

Took the Clutchnet plate out yesterday and threw in an ACT setup.

Perfect, no probs.

It was the Clutchnet plate that was giving me all the crap.

...now to return the clutchnet setup.


Thanks,

-- Dave
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