Am I barking up the right tree? Clutch hydraulics issues...

So this is on the 2011 Audi S4, 6-speed manual. It has a factory hydraulic clutch setup with a clutch master, external clutch slave, and a shared reservoir with the brake master. The car drives perfect, clutch take up is progressive and in the middle of pedal travel, no clutch slippage at any load/RPM, and no grinding or crunching into gears. The car itself has 120K miles and the trans is original. The clutch is a South Bend Stage 2+ Endurance installed by a competent shop (Matrix Integrated in Portland, OR) with a new flywheel in October 2021 about 2K miles ago. The clutch slave is a JXB Performance extended slave and the shifter is a JXB Performance short shifter and plate. Fluid is new DOT4 ATE that I literally just pressure bled.

If you drive around and keep your foot on the clutch at stops, everything works perfect. 

If you put the car in neutral and take your foot off of the clutch, no matter for how long, the car will not want to go in to 1st or 2nd. You can do 3rd/2nd/1st and get it in or jam it with a clunk.

So is the clutch master going bad? There might be a restrictor in the soft line, could that be it? 

To be clear, you can speed shift this thing at 6,000 RPMs all day long and it just slides right into gear with no issues. We did 2 track days with zero issues. You can keep the clutch in at stops and have no problems getting into 1st, it's like butter.

It's only when you put it in neutral at a stop and let off the pedal. Which sucks, because it's the car that sits in Portland traffic twice a week!

If you keep you foot on the clutch but take it out of gear will it go back in?

What happens if you take your foot off the clutch but then pump the clutch a few times before trying to get it in gear?

I had similar problems and found that my clutch disk was bent ever so slightly.  Specifically, one paddle out of four was a skosh off from the other three, was either bent in shipping or manufactured that way.  Installed a disk with verified zero runout, no more issues.

Performance pressure plates tend to trade off plate travel for an easier pedal feel, and as a result tend to be much more sensitive to disk runout.  Takeup will feel normal with a slightly off disk, but the disk will drag a lot when fully disengaged.

Yeah it sounds like a clutch disc or pressure plate issue,  or possibly even some kind of shifter issue. If you had a clutch hydraulic system issue, the clutch would seem to work fine as long as you used it quickly - you could get in and out of gear as long as you pressed the clutch pedal just before. The trouble is that the clutch would release on its own, causing the clutch to self-engage if you kept it in 1st with the clutch to the floor at a stop light for example. Then you'd have to release the clutch and press it back in to get out of gear.

When I bought my Honda it was doing almost the same thing, it ended up being the master cylinder. 

That definitely sounds like a dragging disc.  The weird thing is that you said it engages in the middle of the travel.  Usually when the hydrualics are bad it feels spongy and engages right off the floor.

GameboyRMH said:

Yeah it sounds like a clutch disc or pressure plate issue,  or possibly even some kind of shifter issue. If you had a clutch hydraulic system issue, the clutch would seem to work fine as long as you used it quickly - you could get in and out of gear as long as you pressed the clutch pedal just before. The trouble is that the clutch would release on its own, causing the clutch to self-engage if you kept it in 1st with the clutch to the floor at a stop light for example. Then you'd have to release the clutch and press it back in to get out of gear.

Or alternatively it wouldn't release on its own but the engagement point would be super low or at least very inconsistent.

APEowner said:

If you keep you foot on the clutch but take it out of gear will it go back in?

Yes, like butter.

What happens if you take your foot off the clutch but then pump the clutch a few times before trying to get it in gear?

Still doesn't want to go in to 1st. 

Here's a video of the issue:

If that's not clear or you need something else let me know. The clutch is still under warranty right now. 

In reply to Javelin :

Probably chasing an idea too far, but when you say it goes back in like butter if you keep the clutch depressed, how long are you giving it in neutral before putting it back in gear?

Just thinking through what's happening: As you come to a stop with your foot on the clutch in gear, the input shaft is being brought to a halt. I think there's a grey area in terms of how hard it's dragging, in that it could take a few seconds to spin the input shaft up after neutral is selected. Out and back in and the shaft may still be stopped, but give it a few seconds of being in neutral and it could get spun up by the drag of a bent disc, bad pilot bearing, etc...

Okay, saw the video after I posted.

Try that 1st/neutral/1st thing again, but leave it in neutral with your foot on the clutch for 5-10 seconds before putting it back in 1st... I bet it won't want to go back in.

The new performance slave could be out of spec (slightly larger diameter) so you are not getting enough travel for complete disengagement. With a new clutch the tolerances could also be tight. I would get the specs on the slave you have and compare it to the OE part. Or the new slave could be going bad or was bad out of the box.  
 

Another thing to look at is the pilot bearing. 

I am also remembering something from my time on Motorgeek about some high performance clutches do not tolerate street driving, like the friction material sheds some that embeds in the flywheel and pressure plate because it doesn't get hot like it would with a lot of forceful driving.  I forget if South Bend was on the E36 M3list or the one to get to avoid those problems.  

In reply to Jesse Ransom :

Good question. I'll have to go try longer and longer with clutch in/neutral to see if anything changes.

In reply to dean1484 :

The slave was installed on the car for ~4K miles of the old factory clutch and is the factory bore and housing, just a longer piston. JXB parts are made by Jay Bullington of SCCA Street Mod. Pilot bearing was replaced with new Audi unit by the shop with clutch install.

Pete. (l33t FS) said:

I am also remembering something from my time on Motorgeek about some high performance clutches do not tolerate street driving, like the friction material sheds some that embeds in the flywheel and pressure plate because it doesn't get hot like it would with a lot of forceful driving.  I forget if South Bend was on the E36 M3list or the one to get to avoid those problems.  

The specific clutch we got was supposed to be "the clutch" for street driving. This car is not a drag car or even tuned for more power. We wanted longevity.

Will it go into reverse after the clutch has been out in neutral?  I though I saw that once in the video. 

If it's a hydraulic problem, you pedal will very likely have too much freeplay at the top of the travel, which will feel funky.  Typically, there will be a half inch or less of travel if you push with your pinky finger, before the pressure starts to ramp up.  Too large a slave is possible, but then it would have been trouble from day 1.

Warped disc, cracked pressure plate diaphragm spring, stiff pilot bushing, or oil on the friction material.

In reply to Javelin :

I don't know modern Audis, but I recall the OE clutches in the 80s to 00s basically lasted the life of the vehicle, like they were made of compressed granite or something...  The 385k mile Audi clutch from a car I had still had a ton of life left when I scrapped the car.  I took it apart out of mechanical curiosity.  (The cylinders had no ridge at the top, either, once I wiped the carbon off)

APEowner said:

Will it go into reverse after the clutch has been out in neutral?  I though I saw that once in the video. 

Yes, but not always.

This may be off base, but did the trans shop change the fluid in the trans when they had it? Is it something different than what was in it before the clutch job?

I don't think it's clutch drag. If it was dragging it would start spinning the input shaft when you moved it to neutral, even if the clutch was held in the whole time. I would also expect reverse to be difficult or impossible to get into if the clutch was let out in neutral and then pushed in before trying to go into reverse  

The symptoms seems like the synchro isn't able to slow the shaft enough once it's spinning, which could be the result of the wrong fluid/lube not having enough friction. When moving it's only slowing the shaft and not trying to bring it to a stop, so it's still smooth.

While it might not be the solution, I'd start with an easy thing like fresh gear lube (maybe factory gear lube) and see if it improves. 
 

On edit: I just saw the above post about reverse. I'd still start with a fluid change to the factory lube. 

Have you checked on Audizine or vwvortex?  I'm sure another S4 owner has seen this before.  My last S4 was the DCT and launch control made it a blast.  

Javelin said:

APEowner said:

Will it go into reverse after the clutch has been out in neutral?  I though I saw that once in the video. 

Yes, but not always.

This really doesn't seem like a hydraulic issue.  In fact, I'm not convinced it's a clutch issue.  It seems more like a transmission issue.  I suspect that the 1st gear syncro is acting up.  I like No Time's recommendation of a transmission fluid change as a first step.

In reply to No Time :

Sorry, forgot to mention, factory fluid change was the first thing we did. I even paid the Audi dealer to do it.

No idea if the Audi is front or rear wheel drive, but if it were possible, I would put the car on stands, put the car in neutral and turn the driveshaft while making a mental note of how hard it was to turn.

Then I would repeat with the trans in gear and the clutch pedal depressed. The goal is to see if it is substantially harder to turn in gear with the pedal down than it is in neutral.

Lazy mans way would be to find a hill and roll down doing the same test and compare speed at a fixed point.

If you start the car in gear, on a flat surface,( with the pedal pushed) does it try to move just a tiny bit?