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Brake pedal dead zone

Old 09-05-2018, 04:58 PM
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Icon5 Brake pedal dead zone

2012 Honda CRZ EX

Issue started with incident:

Was braking over rough road, which is unavoidable in my city, and it got rough enough to skip the tires around. ABS did it's thing and activated as usual - nothing felt odd during this braking action. Next time the pedal was depressed the symptoms appeared. Brake pedal falls rapidly with little pressure, until it gets past a certain point and full braking is available. Brake pedal seems super low by the time this happens. Full panic braking (with abs activation) available with a hard and almost complete pedal press past what I can really only describe as a dead zone.

First thought was air:

Inspected the brake system, no fluids visible anywhere (master, connections, lines, abs modulator, etc... Upper brake reservior filled properly to line, lower reservior attached to master cylinder is fine. Lines between are clear...

Did my full and complete flush in the proper order. I run vinyl tubing from the bleed nipple all the way back to the upper brake reservior, discard the dirty stuff while keeping the reservior full and when the vinyl tube is full of clean fluid I stick it in the reservior and pump for 10 minutes firmly across a closed loop from bleed nipple to reservior. It's still a two man job, someone has to sit by the bleed nipple and make sure the vinyl tube doesn't pop off - the advantage is the volume of fluid you're able to push through the lines by pumping constantly.

Anyhow, absolutely zero change. Big old dead zone in the brake pedal travel - feels exactly the same.

Off to my mechanic - tell him the story and set him loose. Given the context I theorize that it's either the master cylinder, ABS modulator, or some air in an odd spot that I missed:

Mechanic re-does the bleed, no change.

Replaces the master cylinder, no change.

Has a snap-on device that can actuate the ABS solenoids. The procedure is that you provide pressure at the brake pedal, and then hit a button on the device and it uses some CANBUS signal to actuate the solenoids. When you do this there's pushback on the pedal, and it pulses. New symptom discovered: all solenoids except the front passenger provide pushback.

Call the dealer and set up an appointment - remember this part for later: they drop a hint that you might have to activate the ABS solenoid while flushing. Tell my mechanic this and he flushes again but no dice.

Off to the darn dealer:

Dealer flushes as part of diagnostic. They tell me it works now, and there was lots of air in the system. WTF? They tell me 'they have a machine that purges all air and fluid from the lines'. Won't go into any more detail than that, I try to get some more info but no dice. Whatever - time to go pick it up.

Drive off and have a ton more brake pressure - but there's a problem. I have brake pedal sinking. WTF?? It's definitley there. I can stop on a steep hill and after about 5 seconds if I don't increase pressure I begin rolling back. Pedal still seems to sink to a point and then hold. Doesn't feel like a dead zone anymore though, plenty of pressure but slowly lets off.

Okay so I start doing some checking on the empty road to see if I still have panic braking in an attempt to see if I need a tow - keep in mind I've done this, my mechanic did this and so on. Bam, as soon as I've tested panic braking including activating ABS the brake pedal is back to factory.

So... I'm $450 lighter between a mechanic (who forgave me labor and only charged me parts) and dealer. I left the dealer with a less serious problem, fixed it by panic braking... Still not entirely sure what the issue was. Can't find a good diagram of the CRZ ABS Modulator hydraulic circuit but I think the input/output/return to supply is actually handled inside the modulator - if it is I don't think there could actually be enough air volume in there to cause the initial symptoms that weren't relieved by thorough bleeding. Maybe it was just air. The pedal sink after leaving the dealer is weird. Anyone have any ideas?
Alex Daniel is offline  

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