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Discussion Starter #1
My brake pedal has significant travel (1/2 to 3/4 of the way to the floor) before I feel resistance in the pedal and the car slowing. The fluid was pretty old (4+ years/probably had water/air in it) so I decided to take it to the dealer to have them examine the brakes and change out the fluid.

The technician there told me he thought the problem was a bad master cylinder. However, the pedal never would lose pressure and the braking force never decreased when I hit that 1/2-3/4 mark. It seemed (from what I was reading) that the braking force would be gradually lost as fluid leaked past a bad seal in the master cylinder. Would this always be a symptom?

Another interesting thing to note was that only my rear brake pads needed to be replaced even though the fronts and rears were previously replaced at the exact same time. Could this be indicating that the master cylinder is only effectively operating on the rear brakes?

Anyways, I had them do the fluid change anyways and the brakes feel exactly the same (or maybe even slightly worse). Any comments/suggestions would be appreciated. Thanks!
 

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Brake force distribution (front-rear braking bias) is electronically controlled by the ABS/VSC/TRAC ECU and its regulated by the ABS/TRAC Actuator. Did they check the front caliper sliding pins? If one is seized it may cause the low pedal like you are describing. A seized caliper piston may also cause this.
 

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Discussion Starter #3
Brake force distribution (front-rear braking bias) is electronically controlled by the ABS/VSC/TRAC ECU and its regulated by the ABS/TRAC Actuator. Did they check the front caliper sliding pins? If one is seized it may cause the low pedal like you are describing. A seized caliper piston may also cause this.
Took it to two dealers. One said the master cylinder was bad. I didn't buy it because once the pads engage I don't see any fade (ie the car slowly losing the braking force at a stop and the car begins inching forward). I ended up having them change the brake fluid anyways since I knew it was old and that didn't seem to change anything. Another dealer said the back sliding pins were seized (which made sense since the rears wore WAY too quickly). I had them changed them out (along with the pads) and pedal travel may have been slightly reduced.

If I tap the pedal (maybe 1/8-1/4 of the way down once or twice) I can "prime" the brakes and get them to engage right when I start putting putting pressure on the pedal (again this is only immediately after I doing this priming step). That makes me think that there is air in the system but I figured the fluid change (if done correctly) would have solved that problem.

If anyone has any other ideas I'd appreciate it.
 

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I think it sounds like a bad master cylinder too. If you do a complete bleed (including the ABS unit) and know the calipers are in decent shape (slidy pins) then there's not much else for it to be.

Slowly going to the floor with constant pressure is just one mastercylinder symptom. Another is that one stage of the MC is simply blown out and isn't working at all. That's sort of what this sounds like.

Another interesting thing to note was that only my rear brake pads needed to be replaced even though the fronts and rears were previously replaced at the exact same time. Could this be indicating that the master cylinder is only effectively operating on the rear brakes?
Get up to 40 mph and slam on the brakes as hard as you can. See if you can determine which wheels are grabbing.
 

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Discussion Starter #5
Update on this: Took it to a third dealer and they determined that 3 out of 4 calipers had seized pistons. I ended up swapping out all the calipers and put new pads on as well. Brakes feel much better but still not perfect. I suspect maybe some air is in the lines (I used a power bleeder for the job but it still has that "air in the line" feeling) or perhaps the master cylinder is having some issues.
 

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Sometimes if new pads/rotors aren't bedded in right the brakes will feel like the lines have some air in them. Most dealer techs don't invest that much time to do that last step.
 

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Silly question but none of your caliper seals have an ever so slight leak do they? I've seen dust shields removed from around a piston and had it be full of fluid from a leaking seal and it caused some fairly erratic pedal behavior.
 

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Not yet. It may be air in my master cylinder.
2 years of driving around on broken brakes. Wonder how many accidents in this country are caused by poor maintenance like this?

I fixed a girls Accord the other day. Brakes sounded like this. Couldn't even engage the ABS. Got them working nicely. A day later she needed them for an emergency stop. Wouldn't have been able to stop in time if I hadn't fixed them.

I'm guessing you live in a state with no safety inspection?
 

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Hopefully this will help. I'm a Master tech, recently working on a 2008 is230. Soft pedal low engagement. After long diagnosis found bad abs unit, was bypassing internal.
 
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