Master brake cylinder swap

[walt967]

how do you substitute a 1970 240z master brake cylinder for the 311 unit? Can you use the 311 push rod?

[JT68]

What calipers are you running?

[garth]

how do you substitute a 1970 240z master brake cylinder for the 311 unit? Can you use the 311 push rod?

Push rod length/adjustment is critical. I am running GTR calipers with a 510 MC. I could not keep the pedal hard for more than a few 100 miles. The pedal would soften and require a quick double pump for a quick stop. Not an optimum setup for a half blind, slow reacting, old fart driver! I and and others would play with the adjustment but could not get sustained pedal firmness.

I had my car in at Sports Imports for some other work and mentioned it to Ross, who discovered the problem was the push rod was too short and the piston not positioned correctly. An embarrassingly easy and obvious fix

Have to be careful now not to lock up the front wheels.

[dbrick]

And too long is just as bad, it won't let the piston come all the way back and refill from the reservoir. I recall seeing something about swapping the bottom hex fittings from the Roadster cylinder to the new one to get the right fitting threads, not sure if that applies.

[JT68]

If you try to use the 240 Master, it needs to be with big calipers like GTR or 300zx.

The larger 7/8 piston diameter greatly decreases line pressure, so you don't want this with stock calipers.

Email if you need master cylinder technical help! Jim