300ZX 4-PISTON CALIPER UPGRADE PROBLEM....

[REC]

I recently upgraded the calipers on my 90 Q45 with the 4 piston 300zx calipers. My brakes were working fine before but i wanted the increased performance. A member here named Wes told me that i could use the stock brake lines I just needed to shorten the brake line bolt to fit the caliper. After cutting off the heat shield and shortening the bolt me and a friend began to bleed the brakes and everything went as planned until i started the car. When the car isnt running there is plenty of pressure on the brake petal but as soon as the car is running the pedal is mushy and goes to the floor and doens't get any stiffer after pumping it several times. Obviously when driving around the parking lot there is literally no brakes at all as the pedal goes to the floor. I'm basically stuck and have no idea what the problem is. Has anyone experienced this before with this upgrade?

[oneline180]

i dont have a q45, but im pretty sure you are going to want to get a z32 Brake Master Cylinder for your car. Your stock one will have the same problem that 240sx's have when you do a brake swap...its too much for the OEM units to handle the extra pistons...

[EviL inside]

or you could try re-bleeding,,,and making sure the bleed screw on the calipers is on the top.

even with the small difference in the brake master cylinders, it should still stop the car.

[IHeartTurbo]

or you could try re-bleeding,,,and making sure the bleed screw on the calipers is on the top.

even with the small difference in the brake master cylinders, it should still stop the car.

If it needed to be bled, it wouldn't have any pressure with the car off.

[180fan]

master cylinder is needed. Get rid of that mushy pedal.