Clutch Slave Cylinder Install Tips and Bleeding 101 by JHM

[S4 00 2.7]

This should be a sticky in the tech section.

[jaybquick@JHM]

This should be a sticky in the tech section.

Recommend it to the mods. It helps when members suggest this stuff.

[littleredwagen]

Just to add to this thread, I bought a new tool when I did my motor pull for this. I used a Phoenix systems reverse brake bleeder. I first brake fluid in the tank with the slave bleed open to gravity bleed it, then hooked up the reverse bleeder and bled the slave in less than 5 minutes barely using any fluid. It was fast and worked perfect.

[AKS4]

I will be tackling my slave cylinder this weekend and using this as a guide for it. I do have a few questions however.

IS it easier to go from above than below for the replacement? Additionally, how difficult is it to line up the shiftfork with the new cylinder, and is there a simple stupid way or trick to ensure you are lined up?

[mikay1814]

I will be tackling my slave cylinder this weekend and using this as a guide for it. I do have a few questions however.

IS it easier to go from above than below for the replacement? Additionally, how difficult is it to line up the shiftfork with the new cylinder, and is there a simple stupid way or trick to ensure you are lined up?

I found it easier to go from the top. You might be able to get your finger in there as you're sliding it in and feel to make sure the piston is seated in the clutch fork. Just make sure you feel constant pressure as you're sliding the slave cylinder in place. It's not easy to get it in, so if you don't have any trouble at all, there's a chance the piston isn't lined up.

[Mille Bornes]

I also feel it is easier to go in from the top. As far as difficulty lining things up, I feel like it'd be difficult to miss the fork. Before you install, compress the slave with your hand so you get an idea of what it'll feel like

[AWellman]

Okay guys so I intslled my slave 100029291 times and finally I think I got it lined up. any way im bleeding the system and the pedal has no pressure for 1/4 the travel of the pedal then there is pressure as well as a creek.. don't know what it could be because ive never seen the inside of my transmission.

should I just keep bleeding?

[marlboro]

Can someone please tell, do I need to do with this with the engine switched on or off? I tried bleeding with the car off but the pedal does not come up on it's own. What am I doing wrong?

[xalents23]

Do it with the engine off. And make sure the car is level. I just bleed my USP clutch metal slave cylinder using the gravity bleeding method. And it worked perfectly.

[Kenrevo]

Also the feeder for the clutch off the brake fluid reservoir is close to the top so you'll need to keep an eye on it so you don't runout of fluid feeding the clutch.

[FlyboyS4]

I tried bleeding with the car off but the pedal does not come up on it's own. What am I doing wrong?

Like the first page directions say, you may need to pull the pedal back up a few times before it begins returning on its own.

[marlboro]

I have been trying these bleeding methods for hours without success. I tried the gravity bleeding but no fluid comes out. Then tried open bleeder, push pedal, close bleeder, lift pedal. Few drops come out this way but nothing significant and the pedal still does not return on it's own. Also tried lifting the real of the car on stands but doesn't make any difference.

Please any tips are appreciated on what else to try and bleed the clutch.

[Monty23]

You could try getting an extra brake reservoir cap and drill a hole to accept a wheel valve stem. This would allow you to pressurize and push/force the fluid/air through the clutch lines. I wouldn't use more than 10psi though so you don't blow up your brake reservoir.

[marlboro]

You could try getting an extra brake reservoir cap and drill a hole to accept a wheel valve stem. This would allow you to pressurize and push/force the fluid/air through the clutch lines. I wouldn't use more than 10psi though so you don't blow up your brake reservoir.

Currently while trying to bleed I have the reservoir cap open. Does it have to be closed to pressure the system? Also the engine is off. Does it have to be running?

[Monty23]

The engine running vs. non running is going to have no effect on the clutch's hydraulic system. So leave the engine off. Verify that all your fittings are tight ( you don't want air entering the system somewhere), then with the brake/clutch reservoir cap off (pressure is built between clutch master and the slave cylinder, not in the reservoir) and topped off with fluid, open the bleed screw and allow fluid to gravity bleed.

If this doesn't work, try disconnecting the line from the clutch slave and see if fluid will gravity bleed directly out the end of the line. If it does start coming out the line, re attach the line to the slave cylinder and try bleeding it as the first post suggests bleeding a dry/empty hydraulic system.

[Monty23]

And why are you bleeding you clutch slave cylinder? Did you replace the slave? Did you replace the entire line too?

[marlboro]

And why are you bleeding you clutch slave cylinder? Did you replace the slave? Did you replace the entire line too?

I haven't replaced anything but suddenly the pedal was not returning all the way on it's own. It was coming up only halfway. I asked around and the advise was to try bleed the system first. Ones I tried and opened the slave bleeder, the pedal got stuck on the floor and not returning on it's own at all anymore. I don't have power bleeder but all the methods described in this thread failed to work for me so far.

Can I disconnect the slave from the top accessing it through the bonnet or it has to be done from under the car? Too tired and frustrated to try again right now.

[zillarob]

Make sure the pedal is all the way up when bleeding or fluid will not flow to the slave.

[marlboro]

Make sure the pedal is all the way up when bleeding or fluid will not flow to the slave.

Yes, the pedal was all the way up.

[cschuster]

I'm replacing the slave on an 01E later today and have the trans completely out. Can I install the new slave, attach the line, bolt it to the engine, then bleed it? This seems like the easiest way to make sure its done right the first time. My plan was to remove the clutch fork while installing the slave, then carefully slide the fork back on so I can be sure its lined up over the push rod. Anything wrong with that?

[Monty23]

Can I install the new slave, attach the line, bolt it to the engine, then bleed it?

And how do you plan to attach the line to the clutch master without the slave in the car?

If you install the slave before mating the engine to the trans, the slave will line up perfect every time. And If you install it after the trans and engine are mated, you would have to install the slave at a really bad angle to not get the tip of the slave into the cup in the fork.

Bleeding it in the car really isn't tough at all. I don't get why every is having trouble with it? Biggest hurdle is trying to get the air out of a brand new slave. This can be done by holding the slave in your hand next to the trans, open the bleeder and tilt the slave in the right position so that the air wants to exit out the bleeder. Then close the bleeder, install slave, and re bleed to any residual air out of the system.

[cschuster]

And how do you plan to attach the line to the clutch master without the slave in the car?

If you install the slave before mating the engine to the trans, the slave will line up perfect every time. And If you install it after the trans and engine are mated, you would have to install the slave at a really bad angle to not get the tip of the slave into the cup in the fork.

Bleeding it in the car really isn't tough at all. I don't get why every is having trouble with it? Biggest hurdle is trying to get the air out of a brand new slave. This can be done by holding the slave in your hand next to the trans, open the bleeder and tilt the slave in the right position so that the air wants to exit out the bleeder. Then close the bleeder, install slave, and re bleed to any residual air out of the system.

I should have been more specific. Install slave in trans while on the ground. Lift trans up enough to connect the line and put the bolt in. Then attach trans to engine - there's air in the slave so it will be easy to compress. Put all bolts in, then gravity bleed for 30min. Do the pedal/bleed valve trick to get the last of the air out.

If I bleed it like you said, wouldn't that make mating the trans to engine difficult because the slave it now pushing against the pressure plate?

[Monty23]

I should have been more specific. Install slave in trans while on the ground. Lift trans up enough to connect the line and put the bolt in. Then attach trans to engine - there's air in the slave so it will be easy to compress. Put all bolts in, then gravity bleed for 30min. Do the pedal/bleed valve trick to get the last of the air out.

This should work fine, just make sure the DS rear wheel is highest to allow proper path for air to escape.

If I bleed it like you said, wouldn't that make mating the trans to engine difficult because the slave it now pushing against the pressure plate?

I have done it this way 5x or so. Never had an issue. Works great.

[cschuster]

This should work fine, just make sure the DS rear wheel is highest to allow proper path for air to escape.



I have done it this way 5x or so. Never had an issue. Works great.

Great, thank you very much!

[noskill]

I had a hell of a time pushing this thing into the transmission at first because I just couldn't get the right angle on it. I finally figured out a little trick to get the slave in that I haven't seen mentioned here yet so I figured I'd share it.

The new slave came with a plastic cap in the hole where the line goes into it. I wrapped teflon tape around this cap, compressed the slave all the way (outside the car), and pushed the cap in. This created a vacuum inside the slave that made it take almost no effort to push it into place in the transmission. Then I just remove the plastic cap and tighten the line down onto it and bleed as normal.

Hope that helps!

[oppositelock]

I've only installed the slave once, but it was easy, I think because I compressed it before inserting into the transmission. I left the line connected and no air got in the line, so the clutch just worked as soon as the slave slid in.

[verstappen]

Damn... So did I just messed up my install? I removed mine to replace with a new one, I was also installing a new clutch and k04's... once I cleaned the fork and installed the throw out bearing I installed the new slave into place. Replaced the clutch kit and THEN I bolted the trans to the engine. I did this with my b6s4 and had no problems? was that just luck? am I screwed? I really don't want to pull the engine out again...

[ElementR]

New engine build, new clutch, etc all buttoned up and loaded into car. Attached driveshafts, exhaust, etc. Just decided to test clutch. I have no clue how this happened unless somehow the piston deflected off the clutch fork during install but I just slowly pressed the clutch pedal and it went straight to the floor. Of course there is a steady thin stream of hydraulic fluid now coming down from the bellhousing. I am livid that this happened, but seems I have to take the driver side axle out and rip the slave out of there. It took an insane amount of force to get the slave loaded in the first place.

Question: If I get the slave out in one piece with piston still inside the boot, should I be fine with re-installing it with the trans in the car? I don't know the path of the hydraulic fluid but hope it doesn't end up all over the brand new clutch face. Appreciate some feedback. Thanks.

[ElementR]

Just looking at some pics, I don't think the fluid could drip onto the clutch face. So hoping I can get this thing out in one piece. What a major PITA.

[zillarob]

Itll be fine if you are careful and keep all the parts in the boot.
Fluid doesnt usually make it to the disk so you should be good there also.

[ElementR]

Thanks. Back out to start the work. Fingers crossed.

[Seerlah]

Next time, keep the brake fluid reservoir open when putting the slave back. If pressure is too much to push the slave rod in, just crack the slave bleeder screw to relieve pressure. Not that big of a deal. Then bleed clutch slave when done. Don't own a 2.7T, but did it same manner just suggested each time. Then used a Motive Power Bleeder to bleed line to ensure no air.

And as mentioned above, fluid should all be outside the pressure plate. The fork the slave cylinder sits in pushes on the teethe of the pressure plate via TO bearing. So figure everything from there back is where the fluid will be, and will basically need to find a crevice to get onto the clutch disc vs succumbing to gravity...and finding it's way out bottom of bell housing. Inspect the slave though because it is probably trash.

Cheap enough to replace or upgrade to a metal one (don't get cornered by the market...it is just a metal Sachs unit vs plastic one). Put slave in first, line next, keep pedal up, and bleed line with power bleeder. You will lose a lot of your brake fluid during swap. Nice time for brake flush. I personally use Motul 5.1.

[JVD]

You can also reach the slave from the top.

That's how I do it anyway.

[ElementR]

Yeah, I didn't think there was a good chance of the fluid reaching the clutch the more I thought about it... was in a panic at first when I posted. This is just my luck.

Well, it's out. Slave came out less boot so I cringed at the thought of where it was, but to my surprise it was wedged just inside the hole... somehow trapped by the clutch fork. Then I tried fishing the piston out. It was in there pretty much sideways so very tough to straighten it enough (keep in mind the boot is also sideways) to feed it out the hole. After a solid hour or so I finally got it out fortunately. So time for a new slave. It should go in much easier I'd imagine before connecting the hydraulic line this time. Now I see ECS can get the slave in two business days... they are my go to source being so close to me and having pretty much everything I need, but 2 days to get the part so looking into other options. I really want to get this car done by the weekend. For now, it's after midnight and I get up at 6 but I'm cracking a beer after all this. What a headache. Thanks for all the quick feedback.


...and this one is a Sachs so will go with the same again.

[ElementR]

You can also reach the slave from the top.

That's how I do it anyway.

I think I have a decent reach to it from the top too. We'll see how it goes.

[ElementR]

I see what you mean by the market... Looks like the Sachs units are plastic whereas mine is metal. Febi seems to be metal and cheapest overall and in stock at ECS for that matter so seems like a win win.

[Seerlah]

Just brand names. Febi and Sachs makes metal ones. But don't think certain companies manufacture these miracle parts...because they don't. Some they do, and we are grateful for that. But some they simply don't and will mark up the price beyond 100% inflation which I simply think is asinine. Downright highway robbery.

[ElementR]

Agree with you there. The cost of Audi ownership...

[ElementR]

Took 3 attempts, but finally got the new slave installed correctly yesterday. I've been wrenching on cars for darn near 25 years now and cannot come up with a bigger pita to deal with than this part. I found it imperative to unbolt and move the shifter linkage further outboard (towards drive side) so the slave cylinder could be installed straight on. The two attempts prior to doing that resulted in the slave going in and feeling like it was properly seated, but after feeling the pedal with my hand, it was very stiff so I did not proceed and instead removed the slave and re-attacked it. Master never drained so bleeding was easy... just had my oldest son handle the pedal while I handled the bleeder screw under the car. Car is all buttoned up now. Just need to fill fluids and fire up the new engine for the first time. Will have to create a build thread once I have some spare time. Thx again for the feedback.

[ElementR]

And P.S. my arms are seriously scraped up so a long sleeve shirt with tight fitting cuffs would be advisable. I went the short sleeve route and paid the price.