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Weird Master Cylinder Behavior #4674221
02/22/18 11:42 AM
02/22/18 11:42 AM
Joined: Dec 2005
Posts: 1,192
Kennett Square, PA
artbuc Offline OP
artbuc  Offline OP

Joined: Dec 2005
Posts: 1,192
Kennett Square, PA
Re 2010 Acura MDX

This may be perfectly normal but I never experienced or noticed it before. Replaced brake fluid as usual using my Vacula bleeder. Started car and could not get a firm brake pedal. Just kept going to floor. Turned car off and pedal was firm. Turned car back on and braking was normal. Can anyone explain this? At first I thought I let air get into the MC but that just could not have happened because fluid level was always well above ram. Thanks for your thoughts.

Last edited by artbuc; 02/22/18 11:42 AM.
Re: Weird Master Cylinder Behavior [Re: artbuc] #4674235
02/22/18 11:55 AM
02/22/18 11:55 AM
Joined: Apr 2012
Posts: 6,316
MA
Wolf359 Online content
Wolf359  Online Content

Joined: Apr 2012
Posts: 6,316
MA
That's how master cylinders fail. The seals inside the master cylinder went. No fluid loss but the brake pedal go to the floor. Time for a new master cylinder.

Or you still have air somewhere.

Re: Weird Master Cylinder Behavior [Re: Wolf359] #4674267
02/22/18 12:14 PM
02/22/18 12:14 PM
Joined: Dec 2005
Posts: 1,192
Kennett Square, PA
artbuc Offline OP
artbuc  Offline OP

Joined: Dec 2005
Posts: 1,192
Kennett Square, PA
Originally Posted By: Wolf359
That's how master cylinders fail. The seals inside the master cylinder went. No fluid loss but the brake pedal go to the floor. Time for a new master cylinder.

Or you still have air somewhere.


Thx for the quick response. I hope there is another explanation. The car is only 9 years old with 61k miles. MC was working perfectly before I replaced fluid. Also, I was not bleeding air, just replacing fluid so I canít see how there can be any air in the system. Iím wondering if it is normal ECU behavior resulting from the low level switch being activated?

Last edited by artbuc; 02/22/18 12:16 PM.
Re: Weird Master Cylinder Behavior [Re: artbuc] #4674281
02/22/18 12:23 PM
02/22/18 12:23 PM
Joined: Oct 2014
Posts: 1,177
SW Ontario Canada
KGMtech Offline
KGMtech  Offline

Joined: Oct 2014
Posts: 1,177
SW Ontario Canada
Potentially one of the ABS valves was leaking internally in brake hydraulic system, not enough to be a problem in regular use, but after the fluid replacement that portion of ABS system needed to fill up?


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Re: Weird Master Cylinder Behavior [Re: KGMtech] #4674319
02/22/18 12:42 PM
02/22/18 12:42 PM
Joined: Dec 2005
Posts: 1,192
Kennett Square, PA
artbuc Offline OP
artbuc  Offline OP

Joined: Dec 2005
Posts: 1,192
Kennett Square, PA
Originally Posted By: KGMtech
Potentially one of the ABS valves was leaking internally in brake hydraulic system, not enough to be a problem in regular use, but after the fluid replacement that portion of ABS system needed to fill up?


That is what I am thinking now. I applied sealant around the bleeder valve, something I have never done before. Usually I get a lot of air sucking past the bleeder threads such that the fluid looks like foam. With the sealant I got very few air bubbles meaning I put much much more vacuum on the system. I donít have a hydraulic circuit diagram of the ABS but I bet I sucked one of the valves out of position.

Re: Weird Master Cylinder Behavior [Re: artbuc] #4674405
02/22/18 01:50 PM
02/22/18 01:50 PM
Joined: Aug 2004
Posts: 20,515
CA
The Critic Offline
The Critic  Offline

Joined: Aug 2004
Posts: 20,515
CA
You have air in the system, this is a common issue with vacuum bleeders. This is why I stopped using vacuum bleeders and use pressure or manual

Bleed the system manually in the correct sequence (should be lf, rf, rr, lr) and it should resolve your problem.


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Re: Weird Master Cylinder Behavior [Re: artbuc] #4674473
02/22/18 02:36 PM
02/22/18 02:36 PM
Joined: Oct 2017
Posts: 566
Northeastern Vermont
littleant Offline
littleant  Offline

Joined: Oct 2017
Posts: 566
Northeastern Vermont
The critic is correct. Pressure or manual bleed. I believe you got a slug of air when bleeding.

Last edited by littleant; 02/22/18 02:40 PM.

I can't prevent getting old but I REFUSE to grow up.
2010 Mountaineer 4.0
2002 Jeep Wrangler TJ 4.0
Re: Weird Master Cylinder Behavior [Re: The Critic] #4674481
02/22/18 02:39 PM
02/22/18 02:39 PM
Joined: Nov 2006
Posts: 21,262
MA, Mittelfranken.de
Trav Offline
Trav  Offline

Joined: Nov 2006
Posts: 21,262
MA, Mittelfranken.de
Originally Posted By: The Critic
You have air in the system, this is a common issue with vacuum bleeders. This is why I stopped using vacuum bleeders and use pressure or manual

Bleed the system manually in the correct sequence (should be lf, rf, rr, lr) and it should resolve your problem.


^ This


ASE L1, Master. Deutsch Meisterbrief.
Re: Weird Master Cylinder Behavior [Re: The Critic] #4674484
02/22/18 02:40 PM
02/22/18 02:40 PM
Joined: Dec 2005
Posts: 1,192
Kennett Square, PA
artbuc Offline OP
artbuc  Offline OP

Joined: Dec 2005
Posts: 1,192
Kennett Square, PA
Originally Posted By: The Critic
You have air in the system, this is a common issue with vacuum bleeders. This is why I stopped using vacuum bleeders and use pressure or manual

Bleed the system manually in the correct sequence (should be lf, rf, rr, lr) and it should resolve your problem.


You have the right sequence. Have used my Vacula probably 10-15 times to replace and/or bleed brakes. Never had a problem. Just finished a long test drive and brakes worked perfectly...pedal feels great. How could that be if air is in system?

Re: Weird Master Cylinder Behavior [Re: artbuc] #4674494
02/22/18 02:44 PM
02/22/18 02:44 PM
Joined: Oct 2017
Posts: 566
Northeastern Vermont
littleant Offline
littleant  Offline

Joined: Oct 2017
Posts: 566
Northeastern Vermont
I think the air may have bleed back and out through the master cylinder.

Last edited by littleant; 02/22/18 02:44 PM.

I can't prevent getting old but I REFUSE to grow up.
2010 Mountaineer 4.0
2002 Jeep Wrangler TJ 4.0
Re: Weird Master Cylinder Behavior [Re: The Critic] #4674513
02/22/18 03:02 PM
02/22/18 03:02 PM
Joined: Jan 2017
Posts: 2,546
VW Fanboy Island
maxdustington Offline
maxdustington  Offline

Joined: Jan 2017
Posts: 2,546
VW Fanboy Island
Originally Posted By: The Critic
You have air in the system, this is a common issue with vacuum bleeders. This is why I stopped using vacuum bleeders and use pressure or manual

Bleed the system manually in the correct sequence (should be lf, rf, rr, lr) and it should resolve your problem.


How does this happen? I've seen the argument made that air gets pulled in to the system somehow but I have never had anyone with first hand experience describe it in any detail.

I use an oil extractor to bleed my brakes and have never had an real issues but I always seem to get bubbles constantly, especially on the RR caliper.


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Re: Weird Master Cylinder Behavior [Re: maxdustington] #4674521
02/22/18 03:09 PM
02/22/18 03:09 PM
Joined: Dec 2005
Posts: 1,192
Kennett Square, PA
artbuc Offline OP
artbuc  Offline OP

Joined: Dec 2005
Posts: 1,192
Kennett Square, PA
Originally Posted By: maxdustington
Originally Posted By: The Critic
You have air in the system, this is a common issue with vacuum bleeders. This is why I stopped using vacuum bleeders and use pressure or manual

Bleed the system manually in the correct sequence (should be lf, rf, rr, lr) and it should resolve your problem.


How does this happen? I've seen the argument made that air gets pulled in to the system somehow but I have never had anyone with first hand experience describe it in any detail.

I use an oil extractor to bleed my brakes and have never had an real issues but I always seem to get bubbles constantly, especially on the RR caliper.


Right, bubbles come from air being sucked past the threads but it is immediately entrained in the brake fluid and is extracted. The only time I got in trouble was many years ago when I used my Vacula to suck old fluid out of the MC and I went too far.

Re: Weird Master Cylinder Behavior [Re: artbuc] #4675097
02/23/18 07:56 AM
02/23/18 07:56 AM
Joined: Dec 2005
Posts: 1,192
Kennett Square, PA
artbuc Offline OP
artbuc  Offline OP

Joined: Dec 2005
Posts: 1,192
Kennett Square, PA
Originally Posted By: artbuc
I donít have a hydraulic circuit diagram of the ABS but I bet I sucked one of the valves out of position.


Duh, of course I have the hydraulic circuit diagram...it is in the FSM. It looks possible, maybe likely, that I emptied the accumulators. In any event, FSM says no special bleeding procedure required for ABS unit. For kicks and giggles I did manually bleed front brakes (first two in FSM sequence) and got zero air. Did another test drive with repeated hard braking and performance was excellent. At this point I have to conclude all is well. Thanks for your help!

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