Alright so I'm planning on replacing my clutch slave cylinder in a few weeks along with some other parts that I have collected within the last few months. Well a few months ago my clutch master cylinder went bad so I replaced it with a ebay cylinder (works fine) but at the same time I bought a ebay slave cylinder. When I received both parts the master cylinder bolted up just fine, but my slave cylinder would rock back and forth whenever I put my foot on the clutch pedal (the oh **** moment). So I took it off and put my stock cylinder back on and have used that for the last few months, well I feel that the cylinder now is finally coming to its end. So I just now bought a Auto Zone cylinder I received it today and what do ya know it's almost identical to the ebay cylinder. I called my local Mazda dealer and they asked a number in the 150$ range (BS in my opinion). Pictures are attached. Do you guys have any ideas?
In the first picture the ebay cylinder is on the left and the Auto Zone is on the right.
The old looking cylinder is the stock cylinder.

 

what do you mean by "rocking back and forth"?

the replacements look like they should work just fine.

if it's an issue with the rod piece, you can see if the stock rod fits more snugly into the piston cup and obviously swap the boot to the new slave.

 

When the slave cylinder was fully bolted down, my father pressed the clutch pedal (ebay cylinder) inwards the slave cylinder would push backward. The clutch never disengaged so we could pull it out of gear. So in short the cylinder itself moved. I pretty sure it's not supposed to do that. Sorry for sounding like a smart @$$ I just don't know any other way of putting it. Also another problem just came up within the short time I posted this. I bought the Re Speed clutch line (love it), but the thread is too big for either cylinder. I'll post a video if needed (for the clutch line).

 

Okay so out of anger I took the hammer and jammed it into the piston and pushed it back. Now looking back on what I did a couple months ago I kept the piston at the distance I received it at and didn't adjust it so when I filled the system with fluid there was no other place for my piston to go but backwards (if you guys get what I'm saying). So Thursday I'll put my theory to the test ad see what my results are. So now I'm just left with why my Re Speed line won't fit, my stock line fits all three cylinders. I know this is a question for Sam but if you guys have ideas this would help. Maybe I'm stupid?

 

You have a 79 (from looking at yoru profile) and I think the brake and clutch lines all used a
finer thread than the FB (81+). So you need a SA clutch line, not an FB one.

 

Yeah I received the wrong hose. So that fixes that problem, should be smooth sailing from here.

 

if the slave itself is moving on the bellhousing then i can only say the mount bolts aren't tight enough, threads pulling out or an issue with the clutch that is putting too much stress on the slave to move the throwout arm.

worst case, if the issue lies within the slave you can buy a rebuild kit for them at most of the big parts stores for about $8. pop out the retaining clip on the end and you will see just how simple of a hydraulics mechanism these are.

but from the fact that your old slave looks bone dry i am almost convinced that you're looking in the wrong place for your issue.

 

Yeah, I received the wrong hose so that is no longer a problem. About the slave cylinder, I think when I installed the ebay cylinder I put too much fluid in the system . So when I receive the right hose I'll replace the system. I think I solved my own problem . Thanks Karack .

 

If the slave's visibly moving on the bellhousing, the bolts are either 1) loose, or 2) too long (mounting ears on slave too thin, so the bolts are bottoming in their holes) or 3) the holes in the mounting ears are too large.

It simply should NOT move on the housing.