Z32 Fr Brakes & MC = VERY short pedal travel

[floodo1]

OK guys, did the search thing and I couldn't really find anyone talking about my specific problem, only a bunch of garbage about "omg i put a 17/16 MC on and now my pedal is stiff".....

So I have this interesting 1" master cylinder...d00d that I got it from claimed it was from a JDM S14...anyway the interesting part is that the 3rd brake line opening already had the little flare fitting in it so I didnt have to mess with that. It's definately 1" as its clearly stamped on it.

Previously I had stock brakes and swapped this MC in (long story) so I'm used to a "stiff" pedal. At this point the pedal also had the hard stop that I talk about below, it just wasnt so short of a throw. Last weekend, I finally got around to installing 30mm Z32 brakes on the front (with stainless lines all around).

My problem is that now the pedal has VERY limited travel. It has the proper free play at the top but once you take up the slack and actually start braking there is only a small amount of travel before the peddle stops moving. Once it reaches this point you can press as hard as you want and the pedal never goes down any farther. Its as if there is some physical stop preventing it from moving farther.

The trip for me is that a tiny bit before you hit the limit of travel the front tires start locking up, and before that there is significant brakings. so the brakes basically work fine, but the pedal just has SUPER short range of motion.

Also the brake booster works...checked it by holding pedal down with car off, then start car and pedal goes down a bit.

again, the ONLY issue is that the travel is so short. it has free-play, booster works, brakes do actually stop, brakes are NOT spongy, the pedal feel is not too stiff (actually has better sensitivity (like it should) compared to stock brakes).

any ideas?

[Def]

Welcome to the world of fixed calipers that aren't flexing around on their sliders plus steel brake lines. It's completely normal.

Most of the "flex" in the braking system will now be from the brake pads compressing, and some do it more than others.

[floodo1]

Welcome to the world of fixed calipers that aren't flexing around on their sliders plus steel brake lines. It's completely normal.

Most of the "flex" in the braking system will now be from the brake pads compressing, and some do it more than others.

really? short travel that just stops? i mean the pedal stops WAAY before it did when it was stock. wow?

[coreansurfer]

did you get the z32 booster?

[floodo1]

did you get the z32 booster?

stock 1997 manual tranny booster. Again I think i should mention that the problem isnt pedal feel but that the range of travel is low and at the end of that range it STOPS. like i said its as if there is some sort of physical stop there preventing it from moving more.

idk, any other info needed?

[Def]

That's how a brake pedal is suppose to feel - vary braking force with pressure vs. travel.

I have a 1" Z32 MC and full Z32 brakes - it is very firm once the pads engage.

[floodo1]

That's how a brake pedal is suppose to feel - vary braking force with pressure vs. travel.

I have a 1" Z32 MC and full Z32 brakes - it is very firm once the pads engage.

like i JUST said, its not a problem of feel, i.e. its not too firm.....the problem is that it STOPS!

basically, as i push the pedal it goes like this:
free play at top, brakes start to engage about the time the free play is taken up. now the pedal gets its firm feel and the brakes start really engaging. pedal keeps going down, front tires lock up, pedal goes down a TINY bit more, pedal STOPS moving at all (no matter how hard you press).

the entire range of motion here, from pedal at the top to pedal not moving at the bottom is pretty damn small....MUCH shorter than i think it should be, and definately shorter than it was with completely stock braking system.

[coreansurfer]

the z32 booster will give you a bit more play in the brakes pedal

[devnull]

Did you adjust the rod that actuates the master cylinder? There are two rods between your pedal and the MC. The rod connected to the brake pedal is adjusted at the brake pedal and only affects brake booster function. The rod from the booster to the MC is adjusted separately.

What you have to do is this:

Jack up the front until you can spin at least one wheel.
Spin the wheel and feel/listen for brake pad engagement. If it's constantly engaged (constant rubbing sound) then the MC needs to be adjusted. If you only hear the brake pads rubbing the disc a portion of the time, it doesn't need to be adjusted.

To adjust the MC:
(1)Unbolt the MC and pull it forward slowly to avoid damaging the hard lines until you can access the rod and it's locking nut.
(2)Loosen the lock nut and turn the rod clockwise 1/4 turn.
(3)Tighten the lock nut being careful to hold the rod in the same position.
(4)Bolt the MC onto the booster and test the brake system. Spin the wheel and listen for pad engagement. If pad engagement is normal, perform a road test.

If pad engagement is still constant repeats steps 1-4. If it doesn't engage at all, repeat steps 1-4, but at step 2 turn the rod counter-clockwise 1/8 turn.

The MC adjustment needs to be checked whenever you replace the MC. Some argue that replacing stock for stock it isn't necessary, however discrepancies in machining can cause two like components to be dissimilar in performance.

[floodo1]

Did you adjust the rod that actuates the master cylinder? There are two rods between your pedal and the MC. The rod connected to the brake pedal is adjusted at the brake pedal and only affects brake booster function. The rod from the booster to the MC is adjusted separately.



Well the first thing that I checked when i noticed the short stroke was that the pads arent dragging...and they arent. I suppose I can double check this, but I doubt the outcome will change.
This being the case, according to your post I DONT need to adjust the MC right?


Really what it SEEMS like (even though peddle feel probably suggest otherwise) is that the MC is too big, so it builds up a lot of pressure with a short pedal movement and this is limiting the travel of the brake pedal.
Thing is that its "only" a 1" MC :(


Also, neither rod (brake pedal to booster, booster to MC) have been adjusted since I had stock brakes.

I also need to note that when I had the 1" MC with completely stock brakes the same thing would happen, but mysteriously the pedal had MORE travel.
This is what makes the problem so strange....with stock brakes there should be LESS travel because the ratio between MC and total piston area is much higher, and going to Z32 brakes increases total piston area a ton, so that should then make the pedal have MORE travel.

I suppose my question should be changed to "What limits the pedal from moving farther down?" and "is the mechanism that limits how far down the pedal can travel also the same mechanism that adjusts free play at the top"

[floodo1]

btw, thanks for the help so far!

[devnull]

This being the case, according to your post I DONT need to adjust the MC right?


That's right.

After thinking about it, maybe you should check the line pressure at each caliper. You'll need a gauge capable of reading 3000 psi. At least check for fluid flow to the rear calipers.

My mom has an '86 300zx that had a problem with the fronts locking up too easily. It turned out the port to the rear brakes on the MC was plugged and all the pressure was going to the front.