I have lost the master in my 72 240 but have a brand new master for a zx (15/16) bore. The ZX would have had rear disc brakes. Any ill effects if I replace the original master with the zx master? I'd think the proportioning valve would compensate the difference for the pressure for the rear disc but could be completely wrong. Anyone have any first hand info on it?

I am assuming your 72 240 is on stock brakes? I have installed a 280ZX Master Cylinder on a stock brake set up before and I felt the braking point became very low. Then again I did not have a proportioning valve installed. I had to play with the pushrod a bit (adjusted outwards) and that fixed things a bit, but I never got the right feel. It did not matter so much because I upgraded the brakes shortly thereafter.

I haven't had a chance to even see if the fittings work. Recovering from surgery and trying to do what I can (it is driving me nuts!) I can go buy the correct one, I just happen to have the other one for an upgrade on the turbo car at a future time. I was/am certain someone did this already and just wondered what the results were.

As long as the mount holes are over and under (not side by side like some 280s) it'll bolt up. And the F&R hookup may be reversed. Just bend yours to fit and everything should hook up.

I have the 15/16" on my wagon with the ZX fronts and drum rears so what I have should replicate a stock early Z and they work fine.

And again, I doubt what gets called a "proportioning valve" on the early car is a proportioning valve. I believe it's a "circuit failure" switch which is designed to turn on your dash brake light should front or rears lose pressure. I actually talked to a guy from this list who has been into his switch and cleaned it up and got it working. I told him we'd give him a table at Canby next year if he wanted to drive up and sign autographs. Only human I know to have ever opened one of these up......

That switch is mounted under the booster and is not the prop valve. That is in-line between the rear wheels.

For those that have installed larger calipers, a 280 booster and a 15/16 MC makes the pedal respond much better.

You would need to drill new holes to match the bolts on the 280 booster. Not easy but a step drill will have it done in a few minutes. You will like the results.

That block is the rear is not a proportioning valve. The proper name eludes me but it's there to hold residual pressure on the shoes so they stay in close proximity to the drum. Otherwise, the shoes would back well off under return spring pull and require pumping the peddle to get them back against the drum. I swapped in a 280Z booster in my 240Z and the 15/16 MC when I went to 280Z front calipers and 240SX rear calipers. I'm working on putting '90 300Z front and rear calipers in with a 5 lug conversion. Custom 19mm offset rear axles provide plenty of room for the internal parking brake. I hope the MC will provide adequate fluid for those new calipers.

The original master for the '72 is for drum brakes and has a pressure check valve for the rear brakes. The disc brake master from the ZX will not have the check valve. This could lead to problems.

You can get a check valve from Wilwood or other suppliers that installs in-line to allow the use if a disk brake master with drum brakes.

Been there-done that. The pushrod will be too short from the 240 booster in it's original state. The pushrod has a screw on nipple on the end of the pushrod that goes into the MC. There is a longer nipple that i found off of a 73 booster unit that will screw onto the earlier pushrod(it's about an 1/2" longer). If you don't install this you will never get the proper pedal travel.

I did this swap for the wildwood brakes and the difference in the 2 rod lengths meant everything as far as the brakes working properly.

That block is the rear is not a proportioning valve. The proper name eludes me but it's there to hold residual pressure on the shoes so they stay in close proximity to the drum. Otherwise, the shoes would back well off under return spring pull and require pumping the peddle to get them back against the drum. I swapped in a 280Z booster in my 240Z and the 15/16 MC when I went to 280Z front calipers and 240SX rear calipers. I'm working on putting '90 300Z front and rear calipers in with a 5 lug conversion. Custom 19mm offset rear axles provide plenty of room for the internal parking brake. I hope the MC will provide adequate fluid for those new calipers.

Called a residual pressure check valve, Nissan does call it a proportioning valve in everything I have seen. But it as you said is not a proportioning valve.

Dave.