We see this far to much. The Matco master cylinders work well if they can return to the top every time. If not there will be a slight back pressure on the system and the brakes will drag a little. These cylinders have a return spring in them that pushes up on the plunger, if the plunger gets to the top of the cylinder the poppet valve will open and be ready for the next push down.
What we have done to get these pistons to return all the way back to the top is install the same return spring that is inside the cylinder also on the outside around the rod of the plunger. It is a nice fix that works very well. You buy the rebuild kit from Van's, put the new spring that comes in that kit inside the cylinder, take the old spring, put it around the shank of a drill bit that is 1/64" bigger than the rod " 3/8" "and peen it with a small hammer, while rolling it on a steal plate or anvil. This opens the spring up a little tell it slides over the rod nice and easy. Then put a thick nylon washer at the bottom under that spring and a 3/8" caller with a set screw in it at the top of the spring, slid down over the rod. You don't have to press it down to hard, just enough to get it moving back to the top each time. I think our set screws were locked down about an inch or inch and a half down from the top of the rod to get it to work. This also makes the brake pedal feel much better out on the move. Just what we have found that works for us.
Yours, R.E.A. III #80888
Last edited by Robert Anglin : 06-17-2017 at 12:06 PM.