Brakes acting up after Q45 brake swap

[jdm_master_X]

me and another member were doing the Q45 brake swap on my car. all went well. we bled the car under factory specs, no air bubbles or anything. go out for a test drive, the brakes sometimes feel spongy on low speeds, and the pedal dives all the way to the floor when approaching high speeds. it grabs when its off, and grabs hard randomly.

im starting to believe my master cylinder took a dump. someone please confirm this. ive been at MrZabala's house for 12 hours and this friday just sucks...

[Fenvy]

did you bleed it in accordance with sequence?

also, are you sure they are on the correct sides? you can not swap right with left sides.

where did you get the calipers? have they been rebuilt or at least cleaned?

[mrzabala]

The calipers are clean and JDM checked them before all of it. We bled in accordance to the manual so yes with the about the sequence.

[180fan]

Well it was wet and cold this Friday anyway. It could be a master cylinder issue, but I'm still inclinded to believe it's either 1. air bubbles, or 2. your master has indeed taken a dump.

[jdm_master_X]

i bled the brakes for nearly 6 hours with MrZabala. we bled em so many times, drove em so many times, and came out with the same results.

i mean i have to pump the brakes to regain normal pressure, which is an indication of a brake master taking a dump.

what is the typical lifespan of the master cylinder in an S13? a lot of my friends who hit the 100K-110K mark tend to change the master cylinders due to failures.

so what are my alternatives to an S13 master? z32 and which else?

[180fan]

I'd stick with the s13 bmc if you only got the front calipers for the q45, although you can also use a Z31 bmc which is a direct fit for the s13's as well. I'm using that bmc with my z32 calipers...

[jdm_master_X]

what would happen if i were to get a Z32 BMC? how would the pedal feel? isnt the pistons inner diameter bigger compared to the S13, allowing more fluid pressure with shorter pedal travel??
Modified by jdm_master_X at 3:23 PM 12/9/2006

[jdm_master_X]

which z32 BMCs have the 1 1/16" piston?

anyway, for those of you tuning in, my problem is when i step on pedal at speeds past 5-10mph, the brake pedal sinks all the way too the floor, and the car does not stop. i have to pump the pedal to regain stopping power.

master cylinder failure right?

[180fan]

uh the z32 that has the 1 1/16" is the z32 with the label on the side 1 1/16"...

master cylinder.

[jdm_master_X]

uh the z32 that has the 1 1/16" is the z32 with the label on the side 1 1/16"...

master cylinder.

but i thought there were two sizes -- a 1" BMC and a 1 1/16" version, variants dependent on abs and non abs z32s?

[matt4pl]

all z32's have abs, i think its just a model year difference, i would think maybe the brake booster is gone.

[jdm_master_X]

well when i depress the brakes before startup, its firm. after startup, the pedal goes down, meaning the booster is assisting the pedal via vacuum. so i know thats good.

[jdm_master_X]

I'd stick with the s13 bmc if you only got the front calipers for the q45, although you can also use a Z31 bmc which is a direct fit for the s13's as well. I'm using that bmc with my z32 calipers...

are they similar parts or does the Z31 have a different size piston?

[jdm_master_X]

UPDATE!

just finished putting the Z32 BMC as well as the Q45 brakes! even though its a bit spongy, i still get pretty good braking power. just a few more air bubbles to bleed and bam!

[180fan]

the z31 came in a few different size pistons. it is a total bolt on affair for the s13 and handles my z32 calipers with ease.

[jdm_master_X]

yeah absolutely.

whats funny is that you know how ABS BMCs only used two out of three outlets for the brake lines (the middle one is blocked off with a hex fitting), once you open it always remember that it does not come with a cup seal. i had to decimate my old BMC to get one. haha.

but yeah it was a leaking BMC after all. the brakes feel awesome now.