Originally Posted by RotaryRocket88

It's a leak or large air bubble. The master cylinder can leak down the firewall and be almost undetectable. I've seen a number of theads where someone pulled the master cylinder to find brake fluid going into the firewall or even inside near the pedals. If you find it is leaking, it's usually a good idea to replace the master, slave and rubber hose at the same time. Mazdarix sells a braided stainless hose that is better than the OEM line.

Originally Posted by DarrenTRS

If the clutch pedal is sticking to the floor then it's very very likely to be the hydraulics and as well will cause shifting problems particularly trying to shift into first or reverse from a dead stop.

1. Check your fluid level and condition
2. Look inside the footwell where the pedal pushrod goes into the back of the master cylinder and see if there is fluid leaking. [bad master cyl]
3. Look at the slave cylinder and pull the dust boot back and see if it is damp and if there is buildup and dampness around the slave itself [bad slave cyl]
4. Check the condition of the flex hose itself, the outer casing will likely be cracked but check for any tearing, dampness, leakage especially around the ends where it's bolted to the hardline or slave cyl.
5. If you can find someone to help you, open the hood, take the cap off the master cyl reservoir and have an assistant pump the clutch a few times then hold it down to the floor. Look carefully at the slave cylinder to see if it holds still in the extended position, if it begins to slowly return while the pedal is still depressed and there appears to be no leak at the slave cyl and the boot is dry and clean. Repeat the pedal pump and hold and this time look at the master cyl reservoir, watch the fluid level and see if while the pedal is held down to see if the fluid returns back on its own, if it does this is a sign of an internal leak in the master.
6. If no leaks or signs of failure are apparent, flush out the fluid and lines with new fluid and see if that helps.

As always it is the BEST practice to replace everything together so you do not fix one thing then have another fail a week or two later because usually when one fails, the other is bound to be on it's way.

RockAuto.com generally has the best prices available for all the parts you will need, try not to get the cheapest master as even though it will last you a long time, you still want a quality product.

When I did my hydraulics I went ahead and replaced both master and slave, and picked up a stainless braided clutch line from Mazdatrix for about $25-30 shipped and IMO well worth it.

Originally Posted by DarrenTRS

Copy n Pasting an older post of mine but covers nearly all the things to look over when diagnosing a hydraulic clutch failure