Disk brake conversion 521

[521newbie]

I am getting the parts together to do the front disc swap on my 521.
I have the following:

Lower control arms
rotors, calipers, soft lines, spindles, hubs
Custom upper arms (on their way from beebani)
SAE to Metric brake line adapters
Pads
upper arm bushings

A couple questions.. Can/should I use the stock master cylinder, if not what should I use?
I want to make sure I'm not missing anything. This is my daily driver and I can't be down too long. Much thanks for the help.

[yello620]

I would not even consider running the single outlet master cylinder on it with the conversion. They are marginal when with the drum system, the seals are almost guaranteed to fail when you increase the needed master cylinder piston stroke due to the larger fluid capacity calipers.

The replacement master cylinder is going to depend on a couple of things. Are you going to try to get a power booster on it too?

I would probably consider the 7/8" bore 280z master cylinder for non-power brakes. If you are going to install a power booster then i would consider the 15/16" bore master cylinder from a 79/80 280zx.
Even at that, i dont think that either of these are a direct bolt on deal to the 521, but must have mount holes filed to make it fit(i think).

[DRIVEN]

We did the Klotz conversion on my brother's 521 which uses 720 rotors/calipers. Used '79 280zx master. Had to open up the mounting holes on the master cylinder and modify the push rod. It works great.

[521newbie]

Do you mean the holes on the firewall need opened? How was the pushrod modified? Does the hardline fitting need modified to fit the new master cylinder?

[DRIVEN]

The posts on the firewall and the holes in the master cylinder were slightly off. I used a file to elongate the holes. The 521 push rod is "captured" and needs to be pulled off by removing the wire clip at the end of the bore. The mushroom end needs to be cut off and round stock material needs to be welded to the end.
Because the original master cylinder is a single pot style you will have to modify the hard lines. The front lines need to be separated from the rear lines. You should also consider adding an adjustable proportioning valve for the rear.

[AtomChurch]

Originally Posted by DRIVEN

You should also consider adding an adjustable proportioning valve for the rear.

I understand that this is recommended, but is it necessary ? I will eventually do this swap and I am wondering if I should get a valve before hand or just get one when the opportunity comes up. How much more pressure do the disc brakes need?

[DRIVEN]

Might not be necessary. These trucks are really light in the back so the prop valve just allows you to reduce the amount of braking to the rear drums which avoids lockup. I'm sure you can get away without it but they only cost $40. It's not really a matter of pressure as much as balance.

[521newbie]

By separate the lines, do you mean I add a line from the master to where they fork off to front and back? Can I add the proportioning valve to that junction for the rears?
If anyone has pictures or a diagram it would be a big help... Thanks for the info so far..

[DRIVEN]

There is a T on the frame rail. The quick and dirty way is to disconnect the rear line from there and plug the port. Then run a line from the new master cylinder down and connect it with a male-to-male coupler. If you add a proportioning valve, it goes in that line.

[521newbie]

I get it now. Thanks for the description. I'll do that.

[521newbie]

Does anyone know where I can find a non-power brake master cylinder? Everyone I call only has the power master cylinder.

Thanks..

[521newbie]

I'm confused. That's a picture of my stock master cylinder. The picture on rock auto doesn't say if it's for non-power and I don't see any rod/seal in the picture.

[521newbie]

Please read from my OP. I am putting disks on my 521. I was told I could use a brake master cylinder from a 76 280z with non-power. I can't find that part anywhere and I'm wondering what I should be looking for...

[DRIVEN]

I'm not aware of any Zs that were available without power brakes.

[521newbie]

Originally Posted by yello620

I would not even consider running the single outlet master cylinder on it with the conversion. They are marginal when with the drum system, the seals are almost guaranteed to fail when you increase the needed master cylinder piston stroke due to the larger fluid capacity calipers.

The replacement master cylinder is going to depend on a couple of things. Are you going to try to get a power booster on it too?

I would probably consider the 7/8" bore 280z master cylinder for non-power brakes. If you are going to install a power booster then i would consider the 15/16" bore master cylinder from a 79/80 280zx.
Even at that, i dont think that either of these are a direct bolt on deal to the 521, but must have mount holes filed to make it fit(i think).

Where can I get the non-power master???

[yello620]

What you need is a master cylinder for the Z. Your only option is from a power brake vehicle that you will be using in a manual brake application. You are simply deleting the power booster from the system. This is also why the pushrod needs modified.

[521newbie]

Is there a pushrod in it? The picture doesn't have one at all.

[DRIVEN]

Probably not. You'll have to modify the 521 push rod.

[kaliboy96]

can you eloborate on the modification of the pushrod, I used a 280zx master cylinder as well and it makes a wierd clicking noise when I depress the pedal what kind of modification is necessary and do you have photos

[mklotz70]

this link will get you fairly close. You may need to back up or go forwards a bit depending on whether you're logged in at the time.

About 3/4 down the page...the m/c stuff starts.

http://forum.ratsun.net/showthread.php?t=10314&page=7


If I remember right...it's a '79 280zx m/c you want....it was disc/drum. Yello620 may correct me on that...I know I got it wrong last time

[521newbie]

Originally Posted by DRIVEN

Probably not. You'll have to modify the 521 push rod.

Does that mean I need to take the pushrod out of the stock master and put it into the 280 master? From what I understood, just needed to weld the end from the stock master to the 280 master. Is that right?

[kaliboy96]

I checked out the thread, is it really necessary to make this modification, I think mine will work okay without modification. But I am not sure why its clicking.

[DRIVEN]

Originally Posted by DRIVEN

The 521 push rod is "captured" and needs to be pulled off by removing the wire clip at the end of the bore. The mushroom end needs to be cut off and round stock material needs to be welded to the end.

You won't be welding anything to the ZX master. Just extending the 521 push rod.

[mklotz70]

climb under the dash...pull back the rubber boot and watch the linkage as you press the brake pedal....most likely, the ticking is either a worn pin on the clevis, or it's the mushroom end moving in the m/c..........because it's not designed to fit there.

[521newbie]

Originally Posted by DRIVEN

You won't be welding anything to the ZX master. Just extending the 521 push rod.

I'm still not getting it. What exactly am I doing with each master cylinder?