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Brake Master Cylinder

544 Views 9 Replies 6 Participants Last post by  steves280
What is involved in putting a 280zx master cylinder in a 20z?
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I mean 280z
I'm going to do it on the week end. Tech tip to follow.

just did wheel bearings, rotors and toyota calipers (tips on deck)
Why would you want to? It just take more pedal effort to get the same stopping power and even with 4 piston calipers, if the rear drums are adjusted right the pedal travel is fine.
LESS pedal effort. 15/16'' in zx VS. 7/8'' in 280z. small amount of difference, but A difference.

if yours is'nt bad, i'd wait.

otherwise, it's 2 nuts and 2 brake line fittings. some people have had problems, forcing them to adjust the length of the small pushrod, but others had a direct swap.
I'm looking into it because my local Autozone has been trying for three weeks to locate a stock replacement for my '77 280z, and everyone else is asking too much for it. I am also looking into upgrading to the Toyota 4 piston calipers soon and I have seen it advised to upgrade to the zx master cylinder at the same time.
Very hard pedal feel, but I swapped from 3/4 to 15/16 and stock booster on my 24oz
Actually, it would require more effort because of the larger bore in the ZX master cylinder.
Pressure=Force/Area, so if you increase the area, you need to increase the force to get the same pressure in the brake lines.

I'm not saying it's not the right thing to do when putting on the toyota calipers; i don't have any experience with that. but all else being equal, using the zx cylinder will require more braking effort.
ZX master cylinder

Quick hydraulic math calc without taking the brake booster into account.

4 X 48mm dia stock caliper pistons have a surface area of 7238mm^2

15/16" (23.8mm) master piston has a surface area of 445mm^2

7/8" (22.2mm) master piston has a surface area of 388mm^2

This means the brake pedal force multipliers are :

7/8" = 18.7X

15/16" = 16.3X

So 100lb force with your foot produces:

1,870lbs with 7/8"
1,630lbs with 15/16"

Or, you need to press 114.7lbs on the 15/16" to match the same braking force 100lbs you would have pressed on the stock 7/8" master.

However, you will have to move the brake pedal less to apply the same pressure on the brake pedal.
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Unless you feel you have a pedal travel issue, (I didn't doing the toyo caliper swap), there is no good reason to do it.
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