For the Hemi brake experts. I have a real Hemi booster and some sort of C body master cylinder. With the proper tool, I was checking the booster rod and the piston in the master and with the tool the rood sticks out father than what it can go inside the master piston. Is this how the Hemi master is different than the rest of the master cylinders? The brakes work fine and don't drag.

The C body and hemi had similar MC in certain years. What is the casting number of your MC if it is bendix? The primary piston sticks out of the rear of the master cylinder some. So when assembled it will push in. The key is that the "compensating holes are not covered by the pistons in the static position. Once you start applying brakes those holes are closed by the piston seal. If they are closed in static position pressure cannot bleed off when you release brakes.

You are probably missing the metal tang on the back side of the master cylinder that prohibits the piston from protruding. Adjust the push rod so the back side of the piston is flush with the back side of the master cylinder at rest.

There is no tang for Bendix disc MC of that era for B bodies. There is a stop bolt under the MC that keeps the primary piston from coming out, but it does protrude in its natural state. Now if this is a power drum set up that would be different.

This is the master cylinder. It doesn’t have a casting number.

Post a picture of the underside

i would think there would be a snap ring to hold piston in ?

Press the piston into it’s bore until flush with the MC flange. Measure the depth of the piston pushrod bore to the flange, record that dim.
Add the compressed gasket thickness to this spec.

Adjust the booster pushrod length to this spec.

I believe there is an actual tool (looks like a square horseshoe) for this but I performed the op. using Vernier calipers

On the original Bendix master cylinder there is a bolt with a point that screws in from the bottom , this is what holds the guts in the master .

Picture of bottom. This is a new Cardone cylinder, so, I guess that is the reason there isn’t a casting number. I have the special tool to do the air gap with, I guess the question is, is does a real Hemi cylinder have a different piston depth than a wedge one.

My original 1971 MC - the piston sticks out maybe .050”.

71 is a different MC. You said you don't have any braking issues so what the issue? That is the aftermarket that had ports on both sides. The 67 All B thru 69 Hemi had ports to the fender. The 68-70 B non hemi to the engine. Same MC in general terms other than port side. They did some stuff with pistons but subtle and I don't know if you can sense any difference. I have Centric on mine which is to fender side only. The 70 C also used the hemi type but with slightly different pistons internally. The 70 B/E Hemi was a shorter but fatter MC but still 1 1/8" bore.

Well I took the measurement with the tool and even with the push rod all the way in, it still sticks out to far, so it has to be pushing on the piston, but I can't feel anything driving it. I'm just wondering if I really need to find the correct cylinder.

I told you how to check it. The spec given by mopar was for the Bendix booster with a Bendix MC attached. Regardless, the key is that the piston seal sit rearward of the compensation port by .010-.020". When brakes off this allows line pressure to bleed back into the reservoir. Those aftermarket versions do work. Though the ports on two sides does not give a good appearance to me. It is a shame the manufactures went that way to make it a universal fit.

When you hold the MC you can press the piston in flush and look at the compensation ports. You would see the piston minor dia. Press more and the black seal should cover the port. The piston rod in booster set the piston to the proper setting.

I do have Casting # 2225621 Bendix 67-69 Hemi MC core. It has been sleeved with stainless, and I had it as a backup. It just needs to be assembled with a kit. If you are interested, you can PM me.

Here is a master that is currently for sale that is much closer in appearance than that one for a Hemi application. I have used it, works fine.

https://mbmbrakes.com/1962-72-mopar-b-e-body-standard-manual-master-cylinder-kit/