NuclearB18B

i've searched and searched through countless threads about brake master cylinders and brake boosters, but i still haven't found anything concrete.

this may be kinda long...

i just recently installed brembo blanks, goodridge lines, axxis ultimates (F & R), and motul dot 5.1 brake fluid. everything was installed correctly and all the lines were bled thouroughly and properly.

now, when i hit the brakes, the initial bite is good, but the pedal slowly sinks to the floor. it used to do it before all the new parts, but only after i had been driving a while and it was hot outside, not constantly like it is now. but the brakes have worked properly twice but for only like one or two stops at a time in the week that i have had them on.
i performed a few simple diagnostic test as mentioned in my manual and from this thread https://honda-tech.com/zerothread?id=1261970 and this is what i've found...

when i pump the brakes with the engine off, the brake feels like a rock but holding it down causes it to sink to the floor very slowly which says master cylinder problem. but there doesn't seem to be any leaks and i haven't found any brake fluid inside the car.

i also read in one post that if you pump the brakes at idle and it goes up that the brake booster is leaking. i pumped my brakes at idle and the idle rose to about 1200 rpm. i checked the vac hoses on the booster and they seemed to be fine. as well as the check valve. starting the car with the brake pedal depressed makes the pedal sink as well. turning off the engine with the brake pedal depress also makes it sink.

does this mean that both the master cylinder AND the brake booster is bad? or could a faulty master cylinder affect the operation of the booster and make it seems like it is bad as well? thanks in advance for your help.

Deluzional

sounds like a master cylinder to me

matto2413

yea i had that same problem in my teg. and usually its rare for your brake booster to go bad. i have an extra brake master cylinder that i just took off of a car that i striped the other day. IM and ill give it to you for cheap

Gekko

I had the same problem when I first got my DA, was the master cylinder.

JUN1OR

I have that problem right now. (94gsr w/ 150k) If you're sure there's no leak anywhere, I'd put money on it that it's the master cylinder. Read this thread:

https://honda-tech.com/zerothread?id=1272412


You'll need to do some bench bleeding.

EDITx3 = wow I can't spell for ****

NuclearB18B

thanks guys. anyone have any experience with the wilwood brake master cylinder?

JUN1OR

easy killer

NuclearB18B

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by JUN1OR &raquo;</TD></TR><TR><TD CLASS="quote">easy killer</TD></TR></TABLE>

lol...i guess that might be a little overkill.

anyway, i replaced the mc today and it works fantastic. thanks for your help.

Dee A Nine

LOL, I have the same problem... but just been lagging on checking what's really the problem though.. haha.. =\

JUN1OR

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by NuclearB18B &raquo;</TD></TR><TR><TD CLASS="quote">

lol...i guess that might be a little overkill.

anyway, i replaced the mc today and it works fantastic. thanks for your help. </TD></TR></TABLE>

How long it take?

NuclearB18B

about 15 minutes. two brake lines, two nuts holing it on and switching the reservoir from the old one to the new one and bench bleeding. i was actually kinda disappointed that it took so little time.

JUN1OR

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by NuclearB18B &raquo;</TD></TR><TR><TD CLASS="quote">about 15 minutes. two brake lines, two nuts holing it on and switching the reservoir from the old one to the new one and bench bleeding. i was actually kinda disappointed that it took so little time. </TD></TR></TABLE>

update: just replaced mine this weekend. Yeah, that was easy!

Bad news, I replaced a bad master cylinder with a bad master cylinder. it still sinks to the floor. no fluid leaks, just bad friggin luck.

I don't think air would cause the pedal to sink like that, just be mushy, right?