1972 CB 750 master cylinder woes... leaking

[fpcb750er]

I had a leaking master cylinder, after a rebuild with a TASClassicmotorsports (great site and retailer btw!) rebuild kit, now I have a leaking master cylinder with a new rebuild kit in it...

Any ideas?  I've done it twice now, I can't feel my left hand from the circlip-circlip issues, cleaned it in between again. It leaks out the rubber boot side - maybe it's toast.

If it is, what AFTERMARKET NEW Master cylinder will fit?  My bike runs well, looks good, but I can't get it on the road because it probably won't stop...

Leaning toward getting a new one, already burned $60 plus on the kits..

[Re-run]

So it is leaking by the piston on the side? if so, it is usually because there is a lot of crud built up in there. See people love their DOT3 brake fluid but it attracts moisture and causes a corrosion build-up. Best thing to do is reove the master, drain it and pull that piston out. then use a stiff nylon bristle round brush(brass is ok to as long as it is not to firm or large) and run it through that hole like you are cleaning a gun barrel.

[fpcb750er]

Thanks, will try that and also honing the cylinder walls, I won't give up totally yet. At least I'm learning to rebuild CB750 master cylinder in under 5 minutes...:)

[Re-run]

You do not want to remove any metal, just the crusty crud.

[fpcb750er]

Will do, I'm only going to give it this weekend and move onto a new one, the Honda dealer that i get my parts from sometimes said they can help me get an aftermarket using some of their resellers, which I'll do.  thanks for the advice, I'll let you know.

One additional question - use DOT 4?

[fpcb750er]

Cleaned the cylinder real good and now, with a strong light, notice that it is worn.  Thanks for the tip, it's a gonner.  I just bought a new master cylinder off of ebay, aftermarket, but brand new.  Thank you for the tips, it did help in making the decision to get the new one.  I appreciate your time, thanks again.