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Discussion Starter · #1 ·
Hey I’m not sure if this is new with the cold weather or it’s been doing for a while but I just noticed the clutch pedal seems to get stuck like 2/3 of the way up.

The clutch is fully engaged and everything seems fine but if I put my foot under the pedal and give it a nudge it springs up like another inch like it’s getting caught at a certain point.

Not sure if it’s the return spring or something with master cylinder? It’s weird cuz it’s engaging fine so it’s not like other master cylinder issues I’ve read about (I swear I tried searching first lol).

Does it just need some lube on the hinge? Thanks!


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When this happened to me with my Corvette, it was caused by old fluid, and was made worse when the underhood temps were higher, such as when on track for a few laps, or creeping along in traffic. A bleed with good fluid helped.
 

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Discussion Starter · #3 ·
When this happened to me with my Corvette, it was caused by old fluid, and was made worse when the underhood temps were higher, such as when on track for a few laps, or creeping along in traffic. A bleed with good fluid helped.
Interesting, because it seems like it happens more when its cold for me.

Was yours the same symptom where the clutch would fully engage but it just kind of gets stuck just below the top? And if you nudge it it springs up the rest of the way?

I can try bleeding the fluid for sure and it probably is way overdue so Im not doubting you but for whatever reason it just doesn't make sense to me the symptoms I am seeing. It feels more like a mechanical thing with the return spring or the hinge in the pedal itself or whatever.

But thanks for the help.
 

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Yes, it was those same symptoms. The clutch was fully engaged, would not slip under WOT around the track. A small nudge underneath made it spring back up fully, and when I pressed back down it jumped through that slack region and started picking up where it left off.

Another symptom was when it did this, and the pedal was pushed all the way down, the clutch would not disengage, forcing you to make clutchless shifts around VIR or wherever it was acting shitty. Good times.

I agree it feels like a return spring thing, but really the master cylinder does most of the pushing back up. My theory is it's shitty old fluid that doesn't flow as well, and when the master or slave cylinder is very hot (or cold) there is enough thermal expansion to change the fitment or friction or something about how it handles the fluid. So somehow it ends up with slightly less fluid in the pressure portion of the system than it needs, causing the low pedal. I don't have any real R&D to back this up, but bleeding has helped me and others with the same problem.
 

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You should change it out using the Ranger method unless you have a remote bleeder, at least once a year. It's an extremely cheap maintenance item that will keep contaminants from eroding the various seals over time.
 
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Interesting, because it seems like it happens more when its cold for me.

Was yours the same symptom where the clutch would fully engage but it just kind of gets stuck just below the top? And if you nudge it it springs up the rest of the way?

I can try bleeding the fluid for sure and it probably is way overdue so Im not doubting you but for whatever reason it just doesn't make sense to me the symptoms I am seeing. It feels more like a mechanical thing with the return spring or the hinge in the pedal itself or whatever.

But thanks for the help.
I learned last yr from a ZL1 guy about the importance of regularly replacing the fluid in the reservoir. I do mine at a min every oil change with is 3-5k, or before a track day. Using a "turkey baster" to drain the reservoir, clean with brake clean and cheese cloth, refill with new fluid, pump the pedal 150-200 times, drain it again, then refill, pump it 20-40 times and go bang gears. If the car is hot and has been sitting (like between rounds of racing at the track) I will pump the pedal 100 times to move the fluid through the system so the fluid down in diaphragm in the trans doesn't sit there and cook adding moisture if the fluid boils or gets super heated from the clutch assy.. Just passing what I've picked up on..
Good Luck,
Jeff
 

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Discussion Starter · #7 ·
Awesome thanks guys this was very helpful! Yeah I don't have a speed bleeder so Ill do the ranger method.

Luckily it hasn't started not disengaging when the pedal is fully down so Ill try to do it asap. If it starts not disengaging all the way I know it can start damaging synchros in the tranny which is way worse than even damaging the clutch.
 
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Discussion Starter · #8 ·
So I did the ranger method of replacing some clutch fluid and my fluid was pretty low and relatively dark (no big chunks in there like some pictures).
I sucked out the fluid in the reservoir and refilled with clean fluid and then pumped the cluch pedal like 200 times and it doesn't seem to be circulating the fluid at all. I have driven it a bit and it does seem a little bit better but not 100%.

I had read on the corvette forums people stick some tubing on the end of a syringe and thread it down the clutch fluid reservoir line and pump fresh fluid down into the master cylinder to help clear the gunk but the hole in our reservoir looks tiny there is no way to get any kind of tube down there that I can see.

Should I just keep driving it and do another replacement? The fluid still looks 100% fresh in the reservoir even after pumping the pedal a million times and driving... how does the fluid actually circulate? there is just one tiny little hole at the bottom of the cup...
 

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If you get a mity vac ($20 sold online and part stores), it's basically a hand vacuum pump.

Using small plastic tubing that comes with it, (3/8 OD?), you can wedge it onto the small nipple in the bottom of the clutch fluid reservoir.

Pump the mity vac up to around 20mmHg vacuum and it will pull old fluid out from the master cylinder. Having fresh fluid in the reservoir, slowly pull the vacuum tube off and it will pull more fresh fluid in. You'll have to manually pull the clutch pedal back up also and top off the reservoir.

The clutch system IS "self bleeding," but its not efficient. Then remove replace your reservoir fluid more regularly. A large syringe from the cooking section of your grocery store works well for this.

The pedal will raise up as the clutch disc wears over time also.

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Discussion Starter · #10 ·
If you get a mity vac ($20 sold online and part stores), it's basically a hand vacuum pump.

Using small plastic tubing that comes with it, (3/8 OD?), you can wedge it onto the small nipple in the bottom of the clutch fluid reservoir.

Pump the mity vac up to around 20mmHg vacuum and it will pull old fluid out from the master cylinder. Having fresh fluid in the reservoir, slowly pull the vacuum tube off and it will pull more fresh fluid in. You'll have to manually pull the clutch pedal back up also and top off the reservoir.

The clutch system IS "self bleeding," but its not efficient. Then remove replace your reservoir fluid more regularly. A large syringe from the cooking section of your grocery store works well for this.

The pedal will raise up as the clutch disc wears over time also.

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Like one of these?


or do you have a link for a good one?
 

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Like one of these?


or do you have a link for a good one?
I like this one - it's plastic but works well. Looks like prices have gone up....

Amazon.com: Mityvac MV8030 Vacuum Pump : Automotive

The auto stores usually have them for a similar price. They should come with a kit including some hose and a reservoir to catch excess when you draw a vacuum

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Discussion Starter · #12 ·
Too busy with work and travel to buy the mityvac and do the real bleed yet but I have been driving it now a bit more and pumping the shit out of that clutch pedal and have changed the fluid like 3 more times and it does appear to be helping just very very slowly.
After driving/actuating the pedal a few hundred times after fresh fluid in the reservoir I can see a little plume of dark fluid with some suspended little particles coming from the hole at the bottom so Jesse is right, the fluid is somehow circulating or self bleeding but it just happens extremely extremely slow.

Overall what I have learned is I should have been doing this all the time lol. Then im sure it is very effective but once its bad enough I think the real bleed procedure is necessary unfortunately.
 
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Discussion Starter · #13 ·
Im happy to report that my laziness and being busy actually paid off this time. I never got around to buying a speed bleeder but after a few more ranger method fluid replacements from the little reservoir and just normal driving my clutch has healed itself!

Not saying fully bleeding is a bad idea but it looks like doing the ranger method enough times actually can bring it back from the dead more than I thought.

Like Random84 said in a previous post, the master cylinder does "self bleed" but it is just super inefficient (im not even sure how it works) but it does appear the fresh fluid has made its way into all the far nooks and crannies and I can drive normally now when the clutch is cold or hot again.
 

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Glad it worked out! Using the Mity Vac helps purge the system more quickly (in addition to pulling air out) - when you pull vacuum you'll get several CC's of brake fluid to "pull" up into the tubing by the vacuum you've created. Then, when you pull the hose off the reservoir, fresh fluid from the reservoir will be sucked back into the clutch lines and master cylinder. Just a little trick to help the process along in tandem with the "Ranger method" of keeping the reservoir full of clean fluid.
 

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Discussion Starter · #15 · (Edited)
Well it’s back worse than before. It was back to normal for a while and now the pedal is stuck almost to the floor and I can’t even pump the cylinder to even circulate the new fluid this time.

I’m gunna buy a mityvac and do it the right way now. I thought I got lucky but a bunch more crap probably made it’s way into the master cylinder finally and I just need to flush all the fluid

I wish there was a way to just bleed the slave cylinder like most cars but these basically have a hydraulic throw out bearing right? Where the slave cylinder is just inside the bellhousing?
 

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Yes, it is in the bell housing. Fluid gets hot and cooks. I would use Ford High Performance Brake Fluid since its hygroscopic and has a higher building point. Yes, a mityvac is a great aid in getting the old fluid out. Can't emphasize enough to get all the old fluid out. I use three pint bottles to get all the old stuff out so the pedal works properly. Such a horrible design with the throwout bearing in the bell housing. Does not take much to cook the fluid.
 

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Discussion Starter · #17 ·
Yes, it is in the bell housing. Fluid gets hot and cooks. I would use Ford High Performance Brake Fluid since its hygroscopic and has a higher building point. Yes, a mityvac is a great aid in getting the old fluid out. Can't emphasize enough to get all the old fluid out. I use three pint bottles to get all the old stuff out so the pedal works properly. Such a horrible design with the throwout bearing in the bell housing. Does not take much to cook the fluid.
My mityvac comes tomorrow do I just stick one of the nozzles into the hole at the bottom of the reservoir so it seals and draws vacuum and pulls old fluid through into the catch bottle?

My pedal is basically stick to the floor so I can’t really pump it anymore to self bleed so hopefully the mityvac let’s me get enough old shit out.


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Discussion Starter · #19 ·
Well I got the mityvac and hooked it up. I put one of the small cone nozzles on the end of the hose going into the catch can and shoved it in the hole at the bottom of the clutch fluid reservoir.
Then I pulled vacuum and a little bit came out but not much. I tried pumping the clutch pedal when it was under vacuum and the pedal was just all the way at the floor.

I held vacuum for a while and nothing changed. I even went up to 20inHg briefly to see if it would knock something loose (yes I know you aren’t supposed to because it might pull air past a seal but it’s already fucked so I wanted to try).

Now even releasing the vacuum the pedal is all the way to the floor there is zero disengaging the clutch where before it would at least let it disengage and shift. Now it’s 100% undriveable

I think the inlet to the master cylinder must be clogged with shit or something? That’s why the self bleeding wasn’t working either. It seems like the master cylinder just won’t refill.

Anyone have experience with this? Do I need a new master cylinder?
Or is there a way to take out the MC and clean it? Or take it out and bleed the slave cylinder?

I didn’t get the bleed tool that will do positive pressure but would that help to push pressure on top of the reservoir to force the master cylinder to fill up again?


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When you have vacuum on the system the pedal will not function properly. Trying to pull the pedal up while under vacuum may have just pulled air through the slave, and given you the dead pedal.

The idea is to get old air and old fluid out so it can be replaced by fresh fluid in the reservoir.

Apply up to 30mmHg vacuum, with a reservoir of new fluid. When the pedal is all the way down and no more fluid comes out, remove the mity vac hose and that will "suck" new fluid into the master.


Repeat a few times.


Only pull the pedal back up, and check fluid levels once you have removed the mity vac.


Look for leaks on the lines or slave. Check pedal function.


Report back.

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