What is the correct master cylinder for manual disc

340sFastback said
I needed a new master cylinder and found this thread with the search. I have the factory 4 piston disc set up. Based on the above post I ordered a master cylinder for a '73 Duster 340 with power disc brakes. Its a Raybestos Part Number MC36406 which is a new "Professional Grade". www.rockauto.com has them. What was on my car was a 1 1/16" and it took excessive foot pressure even on moderate stops. I bench bled, installed, then pressure bled the system. I took it for a drive and the pedal does travel a bit more. But it takes way less foot pressure to stop the car. And it can lock up the tires where as before it could not.

It bolted right in and hooked right up to my reproduction brake lines without issue. Notice how the rear is curved and the front is square. Opposite of how the stock '69 ones were.

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Reading old posts to see if it helps my issues, I remember back in the 80s having a problem coming up with a replacement MC for my 69 KH manual front discs. I think I used one speced for 70 cuda manual discs, anyway, takes a lot of foot pressure to slow down and won't lock up. The lid leaks, probably indicates air in the system. I seem to remember the original being equal with square lid but memory is the first thing that goes. My question: go with the 73 power one or get a original?