Some years back there was a serious error in Napa's database, showing that clutch master & slave master were the same unit! Not so, as either the bore or stroke length or both were different between the two. If they pulled that on you, like they did on me, then swapping out for another doesn't help, if they match parts to existing. I complained enough to them that they corrected their error & have since listed different units for the last 10+ years. Take a look at part numbers on your clutch & brake master and make certain they're different numbers.

It's important to get your free play correct on both the master & the slave. If you don't then the cylinders may always be short-stroking. You could get by with a brand new cylinder but after some clearancing from age things go downhill. If the piston in cylinder doesn't return all the way home then less fluid is pumped next motion.

You need to have a good return spring on the slave cylinder as well, so piston is forced all the way back, refilling master and prepping slave for next action.

Overall I've had more problems with slaves than masters, as mentioned by Trey. Also fluid contamination can have a big impact on clutch ops. Water in the system naturally migrates to the bottom, causing corrosion in slave and fluid compression problems.

I've found again & again that these hydraulic clutches can require much more bleeding than a guy would think. Somehow the air entrained in system doesn't want to move to bleeder and it can take a whole bunch of fluid and a proper method to get them bled satisfactorily.

Finally, don't overlook the possibility of bad fluid lines or connections after all these years, slowly leaking air into system over time.

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