Description: Bendix Disc Brake Master Cylinder Piston Stop Screw -Fine Thread-
Year: Jack's comments below
Model: Mustang, Shelby, & Boss 302 (except Boss 429), MOPAR
Model Options: All with disc brakes 
Thread: 5/16-24 (Fine Thread)
Quantity: 1
Location: Bottom of brake master cylinder

Accuracy Rating: 8
Best Repro Available: YES

Jack's Comments:

OK, you found what looks like an original Bendix master cylinder, but it has a hex headed stop screw that’s fine thread. What you most likely found is a 1972 or older (exact date not known) Ford or MOPAR master cylinder that came with either a hex or button headed stop screw with fine threads. The master cylinder looks just like the earlier version in every way but the stop screw is slightly different. You have some choices. You can find an earlier version with the course thread stop screw, tap the bore to accept the correct larger headed stop screw we sell (see notes below), or use one of the two sizes we offer that look just like the course thread version, but the head is slightly smaller (5/16 - 24 has the same size dome head). Will a judge figure it out, probably not since most judges only feel for a piston stop that has a rounded head. 

NOTE: We suggest you don't rebuild your master cylinder yourself. We recommend using a professional re-builder that’s familiar with vintage master cylinders.

Check out our Factoid Section on how to identify an original master cylinder.

NOTE: Boss 429 master cylinders had a fine thread hex headed piston stop screw.

Notes from a friend who owned a vintage master cylinders rebuilding service:
Q: Any tips on tapping out the smaller 1/4 - 28 stop bolt to accept the larger 5/16" - 18 stop bolt?
A: On a non-sleeved cylinder, there is an annular groove down the bore at the stop bolt location.The factory does this to keep the sharp edge of the hole from cutting the seals on the secondary piston as it goes into the bore. On these cylinders, it would be safe to drill the hole larger and then knock off drilling flash with a hook pick.

When I sleeve cylinders, the holes get thoroughly deburred in my medium honing step with the dingleball hone, so I don't duplicate the annular groove. On sleeved cylinders the holes should not get drilled larger unless the holes are similarly deburred on the inside.