Proportioning Valve

I read with interest the past threads on disc brake proportioning valves. While rebuilding my master cylinder and front disc brakes, I thought it would be prudent to also do the proportioning valve. I ordered the kit for the late model version from NPD and installed it. It leaked (it didn't leak prior to the rebuild). I sent the valve to Mark Furrier in Mass. He had told me that he was seeing valves with a 3/4 inch O-ring on the piston instead of the proper 11/16 inch. It turned out that that was the issue with mine. It seems that the kits from NPD have the wrong size piston O-ring. It should be very difficult to put the proper size O-ring on the piston; so much so that Mark camfers the end of the piston, soaks the O-ring in brake fluid and heats it up to get it to go on. If it goes on real easy, it's likely the wrong one. Just a caution to all who get thier kit from NPD.

Z.,

I also am having mine re-sleeved, by Mark, as a precaution, even though the bore appears to be OK. Just want to be done with it.

BTW, I'm a newbie to the K code world and have found a wealth of good info on this site. Thanks to all.

Wayne