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Old 11-30-2016, 08:20 AM   #1
Sh3rpak!ng
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bizarre inconsistent clutch pedal pressure

So recently my master cylinder seemed to be going out. I was having inconsistent clutch disengagement and would have to pump it a few times to get good functionality. The slave cylinder is brand new (febi brand iirc) as of a few months ago.

So I installed a new febi master cylinder and now have some very bizarre pedal pressure issues. Not really sure how to describe this. When cycling the pedal with my hand, lifting it up and then pressing down, 4/5 times it feels normal, normal pressure and disengagement effort, but sometimes I get ZERO pressure and the pedal will literally fall to the floor. I mean no pressure whatsoever, it feels like it's just hanging loose as if it's not bolted to the master at all. I lift the pedal, press again and pressure is normal. Sometimes when it "misses" it'll fall straight to the floor, sometimes it catches halfway and feels like normal pressure from there.

This feels very different from, for example, after installing a new slave that needs to be bled and the pedal is soft and travel is longer than normal.

Is the new master cylinder bad?
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Old 12-04-2016, 09:23 AM   #2
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Sure sounds like it- like the seals are occasionally just not sealing.

I haven't had that happen before...

...and yeah, I'd try another master. See if you can get a FAG.
Febi has gone... east... for most of their stuff recently. Sadly.

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Old 12-12-2016, 07:11 AM   #3
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Is your clutch pedal spring loaded on the back? The pedal will pull toward the floor by the spring action without hydraulic resistance. How did you bleed the system? The system can be tricky to bleed!
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Old 12-12-2016, 08:16 AM   #4
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Thanks guys for the input/suggestions. Turned out it was a DOA febi master. I replaced it with a brand new FTE unit and while it's still been a pita to bleed, it's working.

Some more info for someone who might come across this thread in the future:
I figured out that the weird pedal action only happened when I pressed the pedal gently. If I jabbed it hard, pressure was fine and the clutch operated fine. My thoughts are that hitting the pedal hard ballooned the seals and made it work. Pressing it softly let the seals leak somehow. After I removed the febi master, the fluid that drained out was very dark and contaminated. That MC was only in the car for two weeks and maybe a couple hundred miles and all the fluid was very fresh.

Regarding bleeding technique; initially I just pumped the pedal a bunch of times until I started to feel pressure building. Then I attached the power bleeder, pumped it up and locked the pedal pressed down to the clutch stop holding pressure. Wriggled under the car and cracked the bleeder on the slave and let it bleed until no more bubbles came out. I did this a couple of times, each time the pedal built more pressure higher up in its travel. Right now it's working, but feels a bit inconsistent so I'm thinking it probably needs another round of bleeding both the MC and the slave.

Any further tips for bleeding both MC and slave are much appreciated. I might have a helper on hand this week to pump/press/hold the pedal while I'm under the car instead of using the pedal depressor tool.
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Old 12-12-2016, 08:52 AM   #5
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The easiest way to bleed the master on these cars is to reverse bleed. Put brake fluid in a pump-type oil can, run a little hose from the can to the bleeder, open the bleeder, and pump the fluid up to the reservoir. Another way is to run a long hose from a reservoir or funnel to the bleeder, raise the reservoir to windshield level and let it gravity bleed, takes longer but still works.
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Old 12-12-2016, 09:52 AM   #6
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Originally Posted by varg View Post
The easiest way to bleed the master on these cars is to reverse bleed. Put brake fluid in a pump-type oil can, run a little hose from the can to the bleeder, open the bleeder, and pump the fluid up to the reservoir. Another way is to run a long hose from a reservoir or funnel to the bleeder, raise the reservoir to windshield level and let it gravity bleed, takes longer but still works.
Hmmm I'll give this a try. Is it a special sort of pump?
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Old 12-12-2016, 03:52 PM   #7
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I used a 50mL syringe with some clear tubing over the end. Bench bled it beforehand so there really wasn't much air to begin with.
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Old 12-12-2016, 07:29 PM   #8
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Quote:
Originally Posted by Sh3rpak!ng View Post
Hmmm I'll give this a try. Is it a special sort of pump?
Something like this
https://www.amazon.com/GOLDENROD-707...dp/B00004YK76/
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Old 07-23-2017, 12:56 PM   #9
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Thread revival... still having issues

No doubt the febi clutch master was bad and that helped quite a bit. But I am still getting some inconsistent operation. I replaced the MC again (under warranty) which made no difference. On this install I bench bled, gravity bled, pumped the pedal, and pulled the slave out and pumped the shaft on it. No difference at all.

The issue I have now is that the system "works" but I have an inconsistent engagement point. Sometimes the clutch grabs right off the clutch stop, sometimes I let it out an inch before it grabs, sometimes a half inch... it's really irritating especially with the twin plate clutch being an on/off switch. I've been trying to find some pattern to the inconsistency and it seems that if I fully release the pedal and then push it hard to the stop, I get the most "travel" as in the clutch grabs an inch off the stop. When I'm in stop/go traffic and doing a lot of clutch modulation (clutch in, out, in, out) and sometimes not fully releasing the pedal is when it seems to lose pressure and grab closer and closer to the clutch stop. If I'm not expecting it to grab so quickly it surprises me and it's a jerky start off the line at a stop and I look like an idiot who can't drive manual. It's especially annoying on a hill where I can't risk rolling backward and have to give a lot of throttle to make sure I grab and go forward, slipping the clutch a lot.

Sooooo being that I recall installing a febi clutch slave, does it sound like perhaps the slave is also bad? I can't really imagine some sort of mechanical issue that would cause such inconsistency. I would think if this was a mechanical issue it'd either work, or not.

I already have a brand new FTE clutch slave ready to go in, just wondering if anyone else has a thought. This is irritating the living shit out of me.
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Old 07-23-2017, 01:10 PM   #10
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Id say try a new slave since you have it. if you can while the slave is off, put a screwdriver in there and try to push the fork, see if theres something off. Get some fluid thru the system and bleed it. then, if you still dont want to take the trans off, get an inspection camera, and look inside the bellhousing while someone actuates the clutch.
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Old 07-23-2017, 01:21 PM   #11
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Thanks, I'm aiming to replace the slave monday/tuesday. Fingers crossed that's it. Honestly, pulling the trans isn't a big deal to me anymore. I've done it so many times and made many modifications to make it easier. I'd estimate I can have it off in an hour. Though that's the last resort here.
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Old 08-01-2017, 11:54 AM   #12
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So I changed the slave for a brand new FTE unit (FWIW the one I pulled out was also FTE). Bled it and there's no change. Same symptoms. Am I crazy or does this seem really weird? I just can't imagine mechanically what would be going on to cause such strange clutch behavior. If I fully release the pedal and stomp on it, I get what feels like full travel and clutch release. But if I ride the clutch pedal a bit (like when in traffic) it doesn't seem to always fully disengage and the clutch grabs RIGHT off the stop.

Guess the next step is pulling the trans....
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Old 08-01-2017, 12:35 PM   #13
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Maybe the plastic TOB couldn't handle the much stiffer twin disc.
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Old 08-09-2017, 12:50 PM   #14
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Paying closer attention to pedal feel... at the very top of pedal travel there's like 1/4" of dead movement until I feel resistance/pressure. Is this normal? I also noticed that if I just stab the pedal only moving it about 1", it feels like sometimes it builds pressure and "grabs" at a point a bit higher than other times. Maybe this is the root of the inconsistency? It kinda makes sense to me that somehow, the clutch master is pushing slightly more or slightly less fluid depending on how hard/quickly I hit the pedal. Question is, why. Am I inept at bleeding my clutch system, is there a slight manufacturing defect with the last 2 FTE MCs I've gotten (amplified by the very sensitive clutch), or is the pedal geometry somehow messed up causing excessive stroke of the MC (maybe it's not supposed to make a full extension on pedal return?)

It's really infuriating. I've never had an issue bleeding a clutch system before and I've been far less thorough about it in the past.
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Old 09-06-2017, 11:12 AM   #15
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Sooo, pretty sure I found the issue. Rather large crack in the pedal box where the clutch master bolts in place.





I think this is case closed. Clutch feels much better now.
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