Brake upgrades done - input needed

[ezzzzzzz]

I completed the four wheel disc conversion on my 71. The parts include 280ZX front calipers/300ZX rotors and rear 240SX calipers/300ZX rotors. I also used the 280ZX 15/16" MC and the stock 280ZX four wheel disc proportioning valve. The old T-valve in the back was gutted. I used MM rear brackets and replaced all flex hoses with teflon/stainless steel braid. I have adjusted the MC pushrod close to where it needs to be (it should be damn near dead-on). The MC was disassembled and cleaned up. I don't believe there is any MC internal leakage. The brakes are fully bled and I can stop the car without panic. There are no external leaks in the system. My brakes are heavy requiring a lot of pedal pressure compared to more modern brakes. Since the car sat for nearly a year I don't recall the original pedal pressure. There is no locking up (front or rear) and it appears the rear calipers are not applying full pressure when looking at the rotor surfaces. I adjusted the cylinders and the parking brake works okay. Are there any suggestions for improving overall performance and rear caliper function for those that have gone before me?

[JimmyZ]

I once installed a non-stock brake system on a Mustang. I've no experience with non-stock Z brakes but just a couple thoughts...

We used an adjustable proportioning valve. It sounds like one wouldn't hurt here.

You might want to try using a 280Z vacuum booster since it is larger. (Less pedal press req.)

Just my 2cents

(Trying to keep this post on top for ya)

[ezzzzzzz]

Okay, I gutted a 280Z NP valve. The only obvious difference to the 280ZX NP valve is the missing brake failure switch. If I reassemble with only the end bolts (no spring/piston) then the brake system is effectively reduced from a true dual setup to a single setup. I like a dual system which is still reasonably operational even if there is partial failure front or rear. If you look at the guts there is a long bolt for the front caliper section. That bolt is hollow allowing brake fluid to move from front to back balancing brake pressure via the piston/spring located in the rear caliper section. I intend to block this hole, leave out the piston/spring and reinsert both bolts. I'll swap out the 280ZX NP valve for this unit. That will separate the front and rear into individual systems retaining the dual brake properties but no proportioning at all. It should still work as the front calipers are much larger than the rear calipers. All of this because I do not have the rear braking I was hoping for. If this does not provide desired results the next step will be replacing the MC (possibly leaking internally?). Lastly, I may end up with an inline adjustable proportioning valve. Crap, I hope this works...... I want to drive, not wrench, for a while!

P.S. I'll consider a booster swap if needed. The pedal presssure is firm but tolerable as long as the brakes actually function well enough to lock them up.

[JimmyZ]

If you don't like the "junction box" of brake lines then run each circuit of the master cylinder separately with Tee unions to split each wheel.

You'll need the adjustable proprtioning valve to dial in your rear brake function. You may be able to get away with a stock Prop.valve but the adj is better in your situation.

Running a dual piston master cylinder into a single block which in turn gets divvied up between the four wheels isn't good construction and begs a bad day.

Either get another block or completely split the system by fabbing some new lines.

My 2c

Jim