Inconsistent brake pedal feel. Doesn't look be your everyday problem

[Bumnah]

I did a z32 brake upgrade on my s13.

Here are the parts that were swapped during the upgrade:

New 1 1/16 brake master cylinderz32 brake conversion linesFront calipers remanufactured aluminum calipers from Advance AutoRear calipers remanufactured aluminum calipers some guy off ebay.Forodo DS2500 brake pads front and rearPowerslot, slotted rotors front and rearz32 ebrake conversionz32 2+2 ebrake cablesichiba 5 lug conversion hubs front and reararp extended wheel studs front and rear.Motul RBF 600 brake fluidRecently swapped remanufactured brake booster from advance auto.Z32 NA rim used. Kind of beat up.Falken Azenis front and rear. 215fronts 225 rears.

Details on the swap:

I had problems from day one. Mainly spongy brakes. It turned out the problem was my front passenger caliper was actually a front driver side caliper. Because the caliper was sitting upside down i couln't bleed the brakes properly. I swapped in the correct caliper. Rebled and I got rid of the sponginess. I have had the brakes pressure bled to be certain there is no air in the lines.

The problem:

90% of the time the brakes feel fine, nice solid brake pedal feel. Then sometimes I have to press further to get the brakes to work properly. It feels like there is air in the lines (but there isn't). If you were to step on the brakes immediately after the initial spongy reponse, you'd get a nice solid brake pedal feel. Sometimes the brakes respond perfectly, sometimes the brake pedals goes 50% lower before you actually get brakes. It hard to determin when the brakes will work properly and when they won't.

What I have done to remedy the issue:

Bled till the cows came home. I swapped in a new brake booster thinking perhaps it was screwed up. I pressure bled the system once afterwards and the problem is still there. I did the brake booster swap this week. The brakes feel solid 90% of the time but if you're driving hard around turns the problem is very apparent. I have replaced the entire brake system minus the hardlines. I'm really not sure where to go from here.

What to do next?:

I'm not sure what else to do to diagnose the problem. I'm hoping you guys can help me on what to do next.

Here are a couple things I am thinking of doing.

Remove the front calipers and pads and see if I see anything strange.Contact Forodo if perhaps my pads are the issue, and see what they say (doubt it's there).Could the suspension have something to do with this problem?

Any help is greatly appreciated.

I'm posting this here instead of basic because I've tried most of your basic things to solve the problem.

Please help.

[My RB25]

The problem won't lie with the pads or suspension. I wish I had the z32 brakes on my car so I could relate, but sorry. Not sure if this would have anything to do with it, but did you bench bleed the M/C before installation? Any fluid leaks?

[Bumnah]

No fluid leaks.The MC was bench bled.

[My RB25]

Any breaks or dry rot on the vaccum line for the booster?

[Vegascorbin]

No Experiance with this but while I read through yor post my thought was faulty M/C. I would check the vacum lines as suggested and then re-blead the M/C then all 4 wheels again.

Blead them until you think you are done than blead them some more.

Just had another thought: Do you have any lines that could be getting to close to the exaust? You couold be boiling the fluid causeing it to not work but then when you get to the car to check it has cooled and all looks ok. Saw that in a race car once. Took us a long time to figure out. No brakes durring the race but all was fine in the pits.

Hope this helps

[My RB25]

Any kinked, crushed or twisted lines or seizing calipers? Also remember the bleeder ALWAYS faces up on calipers.

[ELEMENT692121]

was the master cyclnder new or remanufactured ?? sounds like a mc problem to me .. if you came to me with that complaint id check all the lines really quick if i didnt see anything id change out the mc .. good luck

[MasterOfAngle]

Check the vacuum supply to your brake booster and see if it has a bad brake booster.

[My RB25]

was the master cyclnder new or remanufactured ??

I agree. I've had bad remanufactured mc's before, leaking from the same spot the bad one was That's the reason I only get new mc's.

[Bumnah]

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