help me fix my brakes please, new MC and bled already.

[maddmatt02]

ok, heres the story. we have an 01 accord I was using as my commuter for a couple years, no problems except pedal vibration under braking and eventually also started to cause the wheel to shimmy pretty bad under acceleration. finally decided to fix it and ordered up some parts. However I also bought myself a new car and just left the parts in the garage for quite some time until some family flew out and I went to get the car ready for them to use it. replaced both axles, both front rotors and both pads. (done axles on at least 5 other hondas, rotors on this car as well as countless others and pads on at least 40 different vehicles, never had a problem with the process before and everything seemed to go without a hitch this time)

I go drive the car and the brake pedal was terrible, didnt know how I would have gotten air in the system but figured oh well I'll bleed them. didnt work but I started with the furthest caliper and worked to the closest because I thought thats how it was done. searching revealed its supposed to be the other way around so I reluctantly bled them again knowing it wasnt going to help.

with the pedal still sinking to the floor (but not losing fluid) I figured the MC seals were bad and letting fluid leak past them (had this happen on my 96 and a MC fixed it) but I just installed a new MC and the problem is still there. also I dont remember actually being able to hear the air equalizing the vacuum in the back half of the booster before, but now at a certain position you can hear a constant suction, which makes me think the diaphragm in the booster might be bad... but I have plenty of brake assist, and if the car is off I can pump to build pressure, start the car and the pedal sinks so it seems like the booster is fine by that test.

what should I check next? I assume its not possible for a brake caliper to bleed off system pressure without your fluid level dropping like whats possible with a MC, am I correct there?

 

[maddmatt02]

the fact that the booster is constantly sucking in atmosheric pressure has to mean either the diaphragm or 2 way valve inside have failed, no other explanation, right? so the booster obviously is bad...?

but even with a bad booster the pedal should just be hard to press, but hold pressure like normal, so I feel like Im chasing 2 problems... I know Ive gotten a bad part before, my sister even got 2 duds (I think alternators) in a row once... so maybe my second problem is master cylinder but should I replace the booster first and then diagnose the next problem after that?

https://www.youtube.com/watch?v=Qjcq6dV-ick

 

[Connie]

the fact that the booster is constantly sucking in atmosheric pressure has to mean either the diaphragm or 2 way valve inside have failed, no other explanation, right? so the booster obviously is bad...?

but even with a bad booster the pedal should just be hard to press, but hold pressure like normal, so I feel like Im chasing 2 problems... I know Ive gotten a bad part before, my sister even got 2 duds (I think alternators) in a row once... so maybe my second problem is master cylinder but should I replace the booster first and then diagnose the next problem after that?

https://www.youtube.com/watch?v=Qjcq6dV-ick

You definitely need a new booster if the diaphragm is torn, yes.


Regarding bleeding the brakes:
Had a similar problem on my 02 v6 when I got it.
No leaks but spongy brakes that get firmer when pumped, feels like air was in the system.

Turned out to be air in the master cylinder even though I bench bled it properly. Ended up taking the fittings off, filling the master with fluid while fingers covered ports, starting the car, and having my buddy MASH THE BRAKES AS HARD AS YOU CAN WITH TWO FEET AND HOLD IT!!!!, while holding my fingers over the ports. I got a bit of foam out when he did this, and it came out in front of the fluid that gushed around my fingers. So maybe the air pocket was trapped in the top of the cylinder bore and the volume in the cylinder never went to zero so the air just stayed there when it wasn't pumped aggressively enough. I dunno, I'm no scientist.

Put the fittings back on tightly, then let him take his foot off and rebleed the system. Was fine afterwards, but still not as firm as I'd like; I swear Honda can't build a master cylinder to save their lives. But it doesn't fade and it's been flushed 2 or 3 times since then and still feels the same.

I started furthest caliper from the cylinder like you did, never heard of doing it the other way around.

For whatever reason, though, my Accord is the biggest pain in the @$$ of any braking system I've ever had to bleed. Maybe it has something to do with all that ABS plumbing, I dunno.

Good luck.

 

[maddmatt02]

alright, thanks. got my brake booster sitting in the garage waiting to go in. then I'm going to go back to the bleeding debacle...

 

[Connie]

alright, thanks. got my brake booster sitting in the garage waiting to go in. then I'm going to go back to the bleeding debacle...

Once you get the booster in and are bleeding, try starting the car so the vacuum booster is helping put more pressure through the system with each pump.

 

[maddmatt02]

ok, Ive bled the brakes a TON, nothing was solved. figured I possibly got a bad MC so I got another, bled them a TON, still have the problem. I used a couple peices of flat bar and vise grips and closed off the rubber line between the hard line and caliper at each wheel to eliminate any possibility of it being a caliper since someone told me with the e brake incorporated in the caliper fluid can leak past the piston in there similar to a master cylinder failure (even though I rebuilt the calipers already for my first attempt). still no go and I verified the clamp was holding because I could turn the rotor while the pedal was being pushed.

I just now went out and "bench bled" the master cylinder with it on the booster, removed the clear tubes/fittings and threw in some 10 x 1.0 bolts with washers to plug the MC, pedal holds firm, so I KNOW the MC is fine. now Im going to break the lines loose at the ABS modulator and bleed the lines from the MC to there. next step would be cracking loose/bleeding the lines coming out of it. after that the prop. valve which has me puzzled. in my old CD accord I swapped to rear disc and put in the 4040 and it makes sense, 2 in, 4 out and it can control the pressure differential to the F/R, whatever it is on this car has 2 in, 2 out. so its not really a prop valve, right? I know I had a 95 ford that was 3ch ABS, this is not the case on an 01 accord I assume and since there's 2 separate lines from the modulator for rear brakes that another thing hinting me that this is a full 4ch ABS. but if the rears are controlled independently, and aren't needing the pressure proportioned from the front system, what is the purpose of that block below the master cylinder?

 

[maddmatt02]

oh and yes I also had bench bled the MC before putting it in the first time, just did it again to be absolutely sure I was setup for my plugs to either pass/fail and let me know where to go next.

 

[maddmatt02]

had no helper so all I could do right now was remove lines from MC to ABS and bleed those with the one-man hose/bottle routine then bleed the 4 corners the same way... of course it didnt work but I do now 85% of the time hear a sound like pushing high pressure aerated liquid through a small hole while pressing the pedal during bleeding of the rears. wife got home so I put the bottle back to a rear wheel and had her pump a few times and with a stethoscope it definitely seems to be coming from whatever that valve is under the MC so Im going to see about getting one of those and hope I can finally get the brakes working on this thing. what really stumps me is that it was fine and the problem began after replacing pads/rotors w/o cracking the system loose at all (just c-clamped the fluid back through the lines) and now am having major problems. makes you feel just worthless after youv'e rebuilt engines, swapped engines, done an auto-manual swap, disc brake conversions, etc.. and you cant even bleed your brakes... lol

 

[maddmatt02]

me again... did part 36 replace 6? doesn't list 6, and doesn't mention 36 superceding 6.
http://www.hondaautomotiveparts.com...ER)&catcgry4=KA5MT&catcgry5=BRAKE+LINES+(ABS)

And can a prop valve fail and cause my problem or can it only fail and cause the rears to lock up too easily?

 

[White6GAV6]

Big bump. I know this is a stretch, but does anyone have any ideas on this topic? I’m having the same exact issues cause by the same exact reason, compressing the piston during a brake pad change. I’ve replaced the MC, the proportioning valve, and all the brake lines from the MC to the front calipers and the prop. valve.

I’m at a loss, any help or ideas would be great.