My coworker has pretty much guaranteed to buy my 2010 Forte from me. Since we live on opposite sides of the city and work opposite shifts, I thought I'd drive the car to work today so he could see it in the flesh and possibly test drive it. Everything was fine until I got close to work and hit city traffic. The clutch pedal started feeling "sticky", for a lack of a better word. It had pressure but would stick close to the floor. I could press it down a bit further but it would not return all the way up, except when I shifted to neutral and then it would pop up. It had plenty of resistance on the down travel but it kind of felt like it was binding(?) throughout its travel. Its a hydraulic clutch with a slave on the outside of the bell housing. I just checked the fluid level last night and looked over the engine bay with a flashlight and did not see any leaks. The car shifts great with no grinding or weird noises.
As I got closer to work, I hit stop and go traffic for about the last mile or so. I had to put the car in neutral every stop to get the pedal to rise back up. It was very weird.
So my thoughts are it could be 1 (or more) things:
1. Pedal is binding which prevents the master cylinder from releasing. Maybe the bushings are shot? I'll unhook the pedal from the master cylinder push rod and check for bind.
2. An issue with the hydraulic system. Either slave, master or hoses. I ordered a new OEM slave from Amazon since it was only $30.
3. An issue with the clutch disk, pressure plate, flywheel or release bearing. Please no 
Any ideas? I have Friday, Saturday and Sunday off but I probably won't be able to check things until then.
My son is fighting this with his Xterra. We have tracked it down to the return spring. It has worn notches in the plate it rides in which has changed the geometry. It is getting over-centered and actually holding the pedal about half way down instead of pulling it back up.
In reply to Toyman01 (Moderately Supportive Dude) :
Hmmm, I'll definitely have to check the spring.
At lunch, I went out to the car to check some emails. With the car off, the clutch pedal was nice and springy with no hint of stiffness.
On the drive home, I could feel it start to get sticky again when I hit surface street traffic as I got near my house. It makes it hard to modulate the clutch.
Anything else I should look at? Maybe the master cylinder?
Could be. Start with bleeding the system and go from there.
So I finally got around to looking at this thing. I noticed that when I pulled the car into the garage, I could hear a squeaking noise whenever I pushed the clutch pedal in. I never noticed that before. I got the car in the garage, pulled the airbox off for better access and took a better look.
Neither the slave or master cylinder were leaking any fluid. Nothing was wet or seeping. Fluid level was good in the reservoir. This car shares the brake reservoir for the clutch system. I took a few videos of the slave and the master working:
Slave cylinder in action:
And the master:
I thought maybe the squeak was the slave pushing against the clutch fork so I hit it with a shot of WD40. There was no difference. Then I thought maybe it was the clutch fork or release bearing so I got something to pry the fork away from the slave cylinder. It didn't make any noise.
The weird thing is that I can feel the noise in the pedal. Since its a hydraulic system, that tells me its either the pedal or the master cylinder. I unhooked the clutch arm from the master cylinder and gave it a few pushes with my hands. No noise at all. In fact, the pedal felt exactly like this when I was driving it and it stuck on the floor. I think I've nailed down the culprit.
I'm thinking that the seals are bad which would account for the noise. I'm guessing fluid is leaking past the seals and getting trapped which is preventing the pedal from returning.
A new master cylinder is about $100. It is in a totally stupid location wedged between the brake booster and firewall. It took me a bit to even find the damn thing. I had to follow the clutch line. Alldata says its a 1.4 hour job to RnR the master cylinder. I think I might farm this one out.
Thoughts?
The thing I'm still confused about is that the pedal pops right up when you put it in neutral. That suggests that load on the clutch is affecting what happens.
That, and my limited experience with dying master cylinders is that the fluid doesn't get trapped once it gets past the piston so much as start wetting your carpet. Do note the phrase "limited experience..."
Is there a spec for travel at the fork so you can see if you're consistently getting the right output?
In reply to Jesse Ransom :
Yeah, that is what is weird. If something mechanical with the clutch was not right, wouldn't that affect how it shifts? When it was happening, it still shifted fine with no grinding. It was just when I released the clutch pedal is when the pedal would not return and you could tell the clutch was not engaging all the way (slipping). I've had a clutch disc shred itself and a throwout bearing explode. Both of those times, I could not get the car in gear or shift between gears.
Maybe the pressure plate is not happy? The issue is not constant. It only happens after driving 20 or so miles.
Neither the slave or master are leaking. I've had a master and a slave cylinder fail before, and you are right, they puke fluid all over. Could the piston in the master get stuck in the bore? The return spring on the pedal is not very strong so it wouldn't take much to overcome the spring. I was able to pry the pedal back up with my toe when it started happening a few weeks ago.
I really don't want it to be the clutch disk, pressure plate or throwout bearing because I don't want to drop $600 on a new clutch when I'm selling the car for $2k. My coworker needs it to be reliable because his wife will be driving it to school and back. He is not very mechanically inclined and I want to make sure the car won't fail on them because I would feel horrible.
Where is the "I hate selling cars!" thread?
The fact this gets worse with temperature tells me the throw out bearing is hanging up on the guide tube. You may be able to fix it with some lubrication if there is enough space around the release fork where it enters the bell housing. Pull the rubber boot back and have someone depress the pedal and shoot, dab, squirt, drop, some lube on the guide tube between the bearing and the area it rests when the pedal is released. The hydraulics are good enough to transmit the "feel" all the way out, this is not a hydraulic problem.
EDIT again to say I like his idea better ^^^
In reply to stanger_mussle (Forum Supporter) :
Okay, I think I manage to get some stuff lodged sideways in my head, and you knocked it loose with the observation about the clutch slipping when the pedal didn't come up.
I had been thinking about the effect of the disc binding on the splines, and how that could prevent the clutch disc moving, but it would NOT prevent the pressure plate trying to clamp everything back down unless the clutch disc was walking away from the flywheel and doing the dragging thing against the pressure plate. Which just sounds nuts, because it would have to work its way away from the flywheel then not want to go back. It's starting to sound like a red herring.
Is either cylinder somewhere it's getting heated up during that 20 miles?
What are the odds that it returns better in neutral because you're not modulating the pedal at all when you put it in neutral, but just releasing it abruptly like you wouldn't do in gear?
EDIT: To remove a poorly written and probably useless symptom check.
Bad motor mounts causing a condition you can't see while stationary?
I think you guys might be on to something. Unfortunately, its going to be hard to check if anything is up with the clutch without getting the car on a lift. The hobby shop is closed due to covid and I'm hesitant to take it to a shop because of the cost.
I'm not opposed to putting a clutch in if need be but I would need to do it myself due to the labor costs. A LUK clutch kit is $180 on Rockauto. A genuine Kia throwout bearing is $70.
