Blown Brake Line

[mtnickel]

So I had a scary outing the other day. Decided to do a brake check/test from about 70mph and got on the brakes hard. Pressed firm at first and then attempted to apply more pressure. After slowing to about 20mph the pedal went to the floor. Turns out I burst an old rusted rear brake line.

Now here's a question. Aren't the front and rear circuits supposed to be isolated? Why did I lose braking altogether? Master Cylinder is basically brand new. Or does it require at least a little bit of the pressure to be held.

Anyways, ordered up some copper-nickel lines and will be re-re 'ing them soon. Not fun now that everything is installed. Will have to drop trans, maybe diff, etc.

 

Up next now while i'm at it is a new proportioning valve and found a 280zx rear brake conversion. Maybe get a 1" master as well since the stock was pretty squishy.

[Miles]

Why do you need a proportioning valve?

[mtnickel]

Why do you need a proportioning valve?

The 280zx brakes are a fair bit more powerful than stock drums. Will need to bias them correctly.

 

But alas, plans have changed. Now just doing a full brake upgrade. Figured if I was ripping the car half apart to change the lines, I may as well change the end hardware too.

 

1" d21 master cylinder

82+ 280zx booster

S12w calipers w/ machined spacer, and 84-85 300zx rotors

new 79-81 rear 280zx rotors and caliper rebuild kit (also have proper bracket for this setup).

 

I was a little worried at all the bias problems people say you get with the s12w, but doing a little math, I found that the 280zx had a 60mm front piston. calculating out the area, it is very similar to the s12w piston area. That means, it's 43mm rear piston was likely engineered to be a reasonable match.

 

A lot have bias problems using the s13 callipers as they are often the 34mm version (or at best s14 38mm). So while my 280zx callipers are old, they bolt up, have a nice sized piston, and should bias ok. 

 

For reference sake, I've heard the 82-83 280zx booster bolts up (but just upside down). this allows you to run the other style master cylinders (horizontal mounting points). That being the d21 1" master. So while I may spend a few bucks sourcing a bigger brake booster, the d21 1" master is only $25 from rock auto. Note that it's bigger though and won't fit on the 240z. (I think clutch or throttle mount interference). Another bonus (or caution, depending how you look at it) about the D21 master is that it has 2 Front outputs and 1 rear output port. This way I can bypass all the stock proportioning valve and splitter unit. It also has a built in proportioning valve (yes, built into the master), but it can be bypassed with a few mods. Mostly remove the poppet valve on the end, I will try and document it latter as all the research I did on the same z32 master found no results on people disabling them. 

 

While on proportioning valves, I realized that these things can vary a fair bit. Both the knee point at which they act and the pressure reduction ratio that's part of the valve. Hopefully since it's just a passenger car, the wilwood unit will suffice.

 

Also, tried to figure out if a 1" master would be too big. Well again, I looked at stock setups for a guide. The d21 which i'm taking the 1" master from has the exact same twin 43mm pistons (floating) as the s12w, so pedal pressure wise it should be ok. Definitely would want to pair it with the larger 10" booster though.

 

 

I digress.

Edited May 31, 2015 by mtnickel

[Miles]

Does that D21 master cylinder have a vertical or horizontal mounting flange?

[mtnickel]

 

For reference sake, I've heard the 82-83 280zx booster bolts up (but just upside down). this allows you to run the other style master cylinders (horizontal mounting points). That being the d21 1" master. 

Yes. I tried to imply that above. It is the horizontal bolt pattern.

[Miles]

I would like to use the 280ZX booster and master cylinder on my 72 240Z, but the clutch MC is in the way.