How to tell if you have a bad clutch release fork?
 

1990 GXL

I got into my car today and started to back out of the garage and the clutch goes straight to the floor. It popped back up and after a few pumps it got stiffer, but still felt looser than normal. It feels like it grabs for a couple inches then loses tension, gets loose and drops quickly to the floor. The gears still grab, but it is not smooth as you have to semi force it into gear. No clunks or grinds though.

I bled the clutch thoroughly, but it didn't change anything. With my wife in the car pumping the pedal I can see the slave cylinder moving the release fork back and forth smoothly.

Where else should I look? Seems like an internal problem. Release fork or bearing?

I just replaced the driveshaft and engine mounts. Could jacking the engine up have jammed the slave cylinder against the transmission tunnel or something? Hopefully I won't have to drop the transmission...

your hydraulics are going.Did you check the Fluid level in the clutch reservoir?
..If your clutch is losing pressure it is not a mechanical problem.
It means slave or master is going or shot or on it's way out.
Recommendations of replacing the WHOLE system is usually the best one.(master,slave,rubber line).

+1 on the slave or master

The fork moves though... Normally when hydraulics go there are leaks. There are no leaks that I can see. Maybe I should take a closer look. If there are leaks the pedal will usually stick to the floor too...It just feels loose. No tension.

Fluid level was at the top line. The fluid wasn't clear, but not too dirty.

It has stainless lines BTW so just replacing the bad cylinder. If that's the problem. Could it lose pressure internally? Without leaking out of the seals?

Yes. My clutch master cylinder failed and I had no leaks at all. I also heard it can be leaking, but you never know it because the fluid is leaking into the interior of the vehicle.

"internal leaking" is what's going on. your seals are old, your fluids are dirty and most likely your seals have been damaged due to contaminated fluids. you said you pumped it and it gained pressure again right? thats because when you apply constant pressure, the fluid is going around the seal, while pumping it can create temporary pressure allowing your clutch to disengage. that's your first sign that your seals are on its way out. listen to mystery and your problem should be fixed. its better to fix it now while you still can, instead of getting stranded on the road!

Especially since deteriorating internal seals is the only cause for gray fluid with stainless lines.