300zx brake conversion on 240sx with rear lines causing pedal to go to the floor

[krijohn1012]

HI,

I am gonna go straight to the point....

I am doing the z32 rear brake swap......when I pumped the brake...the padal went to the floor.....

I unhooked the rear brake line from the Master Cylinder to let the Master Cylinder works only with the Front......Everything is fine........And, the padal was so stiff....the brake was really good....

However, once I hooked the rear brake line back to the Master cylinder....the problems happened again...

I just bought the brand new 1 1/16 Z32 Master Cylinder .....Russel stanless steel brake line.....Z32 TT brembo rotor and used set of z32 rear caliper.....

everything I bought seems to be line to me since I bought everything new....

I brought the car to the machanic to have them worked on it...They said they never experienced something like this before......they said it problem might be caused from the Master Cylinder's leaking......but it's brand new...how can it be!!!!!

Please help

[180fan]

got it from somewhere like autozone by any chance or is this an oem unit? It's possible that you got a junk one. Other thing that's possible and more probable is you've got air in the rear lines.

[dousan_pg]

i think u need to bleed it way better.

[krijohn1012]

Yeah we bled the brake....we bled the Master Cylinder.....I really think that there was no air in the line at all.......we have been using 4 bottles of brake fluid so far... but the problem still occurs.......

But the Machanics told me that right after we bled the brake, the padal was so strong....there was a lot of pressure.....however, right afrer you stepped out from the padal just a few second. Then, step on it again.....the padal went down again like there was no pressure....

I thought and tried to find the way to solve the problem all night long.......since mine is a non-ABS one which the main component are Master Cylinder, Power Brake, and Calipers.....

According to my point of view, I think that the problem might cause from the bad Master Cylinder.......since it's possible that the brand new Master Cylinder from the old stock one might have the bad rubber inside the cylinder bore........which makes the MAster Cylinder working less than what it usually does....like 50-60% . Therefore, when I first pumped the brake padal......the padal went down to the floor since there was not enough pressure to push the calipers.....but if I still pumped the padal for the second and the thrid time.....the car stopped fine......

NOw, I am wating for the New MAster Cylinder to put in....Hopefully, changing the MAster Cylinder will bring my s14 back to live again today.....

[Fenvy]

whoa I am not going to read all that but have you considered the brake fluid cooling box?

it often trap air inside and no amount of bleeding will resolve the problem. A lot of peopel just bypass it including myself

[krijohn1012]

how can you bypass it man

Please let me know....that's a good thought

[JeromeS13]

Here's a shot in the dark: make sure the calipers are on the correct side. If they're reversed, you can't get all the air out. Also, what order are you bleeding the four corners in?

[Fenvy]

how can you bypass it man

Please let me know....that's a good thought

I waas wrong, it is for clutch not for brake

[krijohn1012]

The machanic said that they got the brake working now. but I still feel that the air is still trapped inside the brake system.....the padal is better than what I told before....but the feeling still weak.....

I told the machanic about the problem and they told me that it takes sometimes to brake in the new pads and rotors...which I think it's not a good excuse....

I need to get the car back since I need the car to do something....I think I'll just staw away from the problem for a while until I got everything's done....

Then, I'll go back and find out again....

I got the car back now...and I think I have to bring the car back to have them check it again...

Again, if anyone have experienced this problem before, please let me know....I found one person on this board had the same kind of problem like what I have...but noone on this board can pinpoint and answer the problem correctly.......

so let's see how we fix the problem...