Clutch went to floor but now works?? Huh?

This is my son's 2008 Chevy HHR SS.  He called me in a panic a few days ago at 11pm.  He said he backed out of a driveway and went to put the car in 1st gear.  He pushed the clutch and it just went to the floor.  He said he felt no real resistance.  He didn't try to put it in gear for fear of damaging something.  We had it towed to the shop.  Shop confirms the pedal was on the floor when it arrived.  They said they slowly worked the pedal by hand to see what they could feel.  Resistance came back and clutch is now working fine.  Said they've checked and tested for leaks or air and can find nothing.  Ideas?

That's a classic clutch master cylinder failure.  

I had this happen a couple of times on my race car, push clutch in, change gear, release clutch but it stayed on the floor... after bleeding the hydraulics, we went back out and the clutch grenaded. The pressure plate was full of clutch material, which was likely causing it to stay released, and keeping the pedal on the floor (pressure plate spring pressure is what pushes the pedal back up).

Just my experience, your mileage may vary.

I've had this happen with a galled input shaft / damaged throwout bearing.

I had that happen a while ago. Pedal was super soft once, came back and worked fine and I didn't think much of it. Then a month or two later the clutch master cylinder failed.

The car just had the cylinder head fully rebuilt, after timing tensioner failure and valves shook hands with pistons.  A week later this happened.  He said there were no noises, no signs of issues.  It went into reverse fine and when he pushed the clutch as he was stopping, it sank.  I just spoke to the shop again and they said it's still acting fine.  

SKJSS (formerly Klayfish) said:

The car just had the cylinder head fully rebuilt, after timing tensioner failure and valves shook hands with pistons.  A week later this happened.  He said there were no noises, no signs of issues.  It went into reverse fine and when he pushed the clutch as he was stopping, it sank.  I just spoke to the shop again and they said it's still acting fine.  

I'm not sure what the HHR arrangement is, but I'd throw a master & slave cylinder at it, and hope it's not the pressure plate itself.   

On the hydraulic side, it's most likely the master cylinders seals allowing the fluid to bypass the piston and get stuck "inside" of it so the piston can't retract.   It's possible that it even leaked slowly leaked down afterwards either onto the carpet inside or the firewall outside.   But it's likely if you replace just the master, it'll be a lot higher pressure than it used to be, and will shortly blow out the slave.

Does that have any rubber in the clutch line that maybe collapsing internally like a rubber brake line might do?

If there is rubber line, I'd replace it if you do the master and slave. 

Was also thinking an internally collapsing line could cause this, but the MC should be the #1 suspect.

WonkoTheSane said:

SKJSS (formerly Klayfish) said:

The car just had the cylinder head fully rebuilt, after timing tensioner failure and valves shook hands with pistons.  A week later this happened.  He said there were no noises, no signs of issues.  It went into reverse fine and when he pushed the clutch as he was stopping, it sank.  I just spoke to the shop again and they said it's still acting fine.  

I'm not sure what the HHR arrangement is, but I'd throw a master & slave cylinder at it, and hope it's not the pressure plate itself.   

On the hydraulic side, it's most likely the master cylinders seals allowing the fluid to bypass the piston and get stuck "inside" of it so the piston can't retract.   It's possible that it even leaked slowly leaked down afterwards either onto the carpet inside or the firewall outside.   But it's likely if you replace just the master, it'll be a lot higher pressure than it used to be, and will shortly blow out the slave.

IIRC, it has an annular slave cylinder, so replacing the clutch at that point is added parts, little/no extra labor.