Brake pedal goes to floor, engine at idle - DodgeIntrepid.Net Forums - Dodge Intrepid, Concorde, 300m and Eagle Vision chat
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post #1 of 21 (permalink) Old 09-24-2008, 11:08 PM Thread Starter
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Brake pedal goes to floor, engine at idle

Ok, first try this, with your engine running at idle, press hard on the pedal, can you make it go to the floor?


I've just about torn off all my hair trying to figure out exactly what's going on, and for the last year or so I just can't come up with an explaination.

Apparently, many cars do this. A list I've gathered include: Mustang, Corolla, Lancer, Sonata, Jetta. Here're 3 cars that I know for sure that DON'T do this: 1995 BMW 530i, 2005 Mazda 6, 1988 Mazda RX7.

Here are many possible explainations:

1) Air in the system. I've bled the brakes twice in the last year, each time using an entire quart to make sure it's done properly, so no.

2) Bad master cylinder seal. This would also cause the symptom of a "sinking pedal", which mine doesn't do. I have a "spring effect" symptom. i.e. feels like a large spring is under my pedal.

3) master cylinder flex due to thin firewall. I spent 7 hours fabricating a master cylinder brace, and now the MC doesn't even budge when I'm heavy on the brakes. But the pedal will still go to the floor.

4) leaky hoses. No, my fluid level is perfect.

My biggest defence against many speculations is the fact that with the engine off, my pedal is as stiff as the pedal on an F1 car! I can apply about 200 lbs of force, and the pedal barely moves 1/4". This means I have NO AIR in the system, and the MC seal is GOOD.


So, anybody has any idea of what might be causing this on our cars?

The only other thing I can think of is caliper and hose flex, but they shouldn't flex so much that the pedal goes to the floor.

most importance of all though, verify this on your car!!! This is not something you'd likely to notice in normal driving, unless you're on a racetrack

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post #2 of 21 (permalink) Old 09-25-2008, 06:15 AM
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that's very similar to the problem I'm having, except it is very obvious - my pedal goes straight to the floor with almost no resistance.Add a '99 Town & Country to your list!
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post #3 of 21 (permalink) Old 09-25-2008, 07:27 AM
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How hard are you pushing? If you push hard enough you can get any car's brake pedal damn near on the floor. I can get mine about 2 inches off the floor.
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post #4 of 21 (permalink) Old 09-25-2008, 11:08 AM
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well, Crap! I just had a nice post typed out about this, and I hit the escape key... hitting escape is the same as hitting UNDO!

ALL BE WARNED, DON'T HIT ESCAPE WHILE USING 'QUICK REPLY' AT THE BOTTOM OF A THREAD!

Sorry, I'm pissed about that.

Does the car stop o.k.?

O.k. I wonder if you have drum brakes... if the drum brakes aren't adjusted UP all the way, you'll get that problem.

Or, if you have 4 wheel disc, and the discs are warped a bit (not runout that you will feel in the brake pedal). If they are warped enough, they will force the calipers back open greater than needed, meaning you'll have greater pedal travel to full compression than ideal...

A comment on Warped and Runout... To me, what most people call 'warped' is really runout. Runout would be where the thickness of the rotor changes around the circumfrence of the rotor. This would mean that as the wheel goes around, the caliper would be forced open in the thick areas, and allowed to colaps in the thin areas.

With a Warped rotor, the thickness of the rotor stays the same, but rather what happens is that the center line of the edge of the rotor wobbles as the rotor is spun. This would cause the caliper, while under braking force, to slide back and forth on the hardware, creating very little feel in the pedal if any at all... but, under NO braking force, the rotor spinning at a high rate on a floating caliper would knock the piston back into the bore farther than needed, making you have to push the pedal that much farther every time you push on it....

Of course, if you are experiencing the pedal to the floor syndrom after repeated pressings with out driving between them, that shoots my theory out the window...
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post #5 of 21 (permalink) Old 09-25-2008, 07:57 PM
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I actually check this quite often when I'm in my car, but I wasn't even aware of this issue. I had a 1988 Mazdda 929 that had the master cylender go at one point. I would have to have the brake pressed all the way to the floor. If I lifted up just a bit, the car would move. My father regularly drives a 1996 Town and Country but we've yet to encounter this.
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post #6 of 21 (permalink) Old 09-25-2008, 10:53 PM Thread Starter
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Quote:
Originally Posted by 32Intrepid View Post
How hard are you pushing? If you push hard enough you can get any car's brake pedal damn near on the floor. I can get mine about 2 inches off the floor.
Well, that's the thing - this seems to be a design problem. The BMWs I mentioned do not do this regardless of how hard you push.

When you say 2" off the floor, I assume the pedal is actually bottomed out somewhere. i.e. you can feel metal to metal contact, even though the pedal itself is still not touching the carpet.
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post #7 of 21 (permalink) Old 09-25-2008, 10:57 PM Thread Starter
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Quote:
Originally Posted by cdmccul View Post
well, Crap! I just had a nice post typed out about this, and I hit the escape key... hitting escape is the same as hitting UNDO!

ALL BE WARNED, DON'T HIT ESCAPE WHILE USING 'QUICK REPLY' AT THE BOTTOM OF A THREAD!

Sorry, I'm pissed about that.

Does the car stop o.k.?

O.k. I wonder if you have drum brakes... if the drum brakes aren't adjusted UP all the way, you'll get that problem.

Or, if you have 4 wheel disc, and the discs are warped a bit (not runout that you will feel in the brake pedal). If they are warped enough, they will force the calipers back open greater than needed, meaning you'll have greater pedal travel to full compression than ideal...

A comment on Warped and Runout... To me, what most people call 'warped' is really runout. Runout would be where the thickness of the rotor changes around the circumfrence of the rotor. This would mean that as the wheel goes around, the caliper would be forced open in the thick areas, and allowed to colaps in the thin areas.

With a Warped rotor, the thickness of the rotor stays the same, but rather what happens is that the center line of the edge of the rotor wobbles as the rotor is spun. This would cause the caliper, while under braking force, to slide back and forth on the hardware, creating very little feel in the pedal if any at all... but, under NO braking force, the rotor spinning at a high rate on a floating caliper would knock the piston back into the bore farther than needed, making you have to push the pedal that much farther every time you push on it....

Of course, if you are experiencing the pedal to the floor syndrom after repeated pressings with out driving between them, that shoots my theory out the window...
The cars is obviously 4 wheel disk; I'm unaware of and 2nd gens with drums.

The car stops excellent, and under normal braking, the pedal is FAR from hitting the floor. However, what I'm describing is stomping really hard on the pedal, while sitting in the driveway, idling. Even if the rotor has excessive runout (mine doesn't), the piston would've adjusted to it if you're sitting still.

The question is, if you get in your car, turn on the engine, and press really hard on the brake pedal, could you make it go to the floor?

I've duplicated this on atleast one other Intrepid.
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post #8 of 21 (permalink) Old 09-25-2008, 11:01 PM Thread Starter
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Quote:
Originally Posted by cubedtothex View Post
I actually check this quite often when I'm in my car, but I wasn't even aware of this issue. I had a 1988 Mazdda 929 that had the master cylender go at one point. I would have to have the brake pressed all the way to the floor. If I lifted up just a bit, the car would move. My father regularly drives a 1996 Town and Country but we've yet to encounter this.
The thing is, if the master cylinder seal goes, then the pedal would sink while sitting at a stoplight. My pedal remains in the same position regardless of how long I'm on the brakes for.

Also, the pedal is stiff as a rock when the engine is off, with no vacuum boost. If the MC is bad, you'd feel it boost or no boost.

Now, the next time you're in the Intrepid, could you try verifying this?
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post #9 of 21 (permalink) Old 09-26-2008, 12:16 AM
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ive actually never tried flooring the brake as my brakes kick in pretty quickly.

BUT my friends g35 has a similar issue that you are describing, you have to floor the brake to feel something. He Just had the brakes serviced, flushed, new pads and rotors front and rear and its still the same.

I wonder if ABS has anything to do with your issues? I dont see how it would but im just trying to look at it from all angles. I tried my brake after reading this and it wont touch the floor, it comes close to it but even if i press it really hard it never touches the floor as in feeling metal to metal contact. I didnt measure it.

You have to be losing pressure somewhere otherwise your system would explode with that much pressure applied to the brakes.

Engine off, my brake pedal will get very stiff after 1-2 pumps. Is there some sort of brake pump that runs off the engine ? There must be some hydraulic power, perhaps thats a flaw in the system?

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post #10 of 21 (permalink) Old 09-26-2008, 12:27 AM
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Replace the master cylinder, that is all.
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post #11 of 21 (permalink) Old 09-26-2008, 12:33 AM
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Quote:
Originally Posted by RJ View Post
Well, that's the thing - this seems to be a design problem. The BMWs I mentioned do not do this regardless of how hard you push.

When you say 2" off the floor, I assume the pedal is actually bottomed out somewhere. i.e. you can feel metal to metal contact, even though the pedal itself is still not touching the carpet.
Wouldnt necessarily say its a problem, the car stops fine and always has. My dads truck does it too, its a dodge. Its just the way the brake system works. I get about an inch of movement before the brakes apply, and if I step much harder it will lock the tires and kick the ABS in -- that happens about half way to the floor, maybe alittle more.

Its hard to tell if its metal to metal contact or you are just at the maximum pressure of the hydraulic fluid. You can not compress fluid, so it may feel like its metal once you hit the limits of the system.

If your pedal is light and feels spongy, you may have a leak or air in the system. Then it will go all the way to the floor with ease. I have to put quite a bit of force into mine to make it go to the 2" from the floor.


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post #12 of 21 (permalink) Old 09-27-2008, 04:28 AM
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tried it again today, i think i feel the max pressure of the cylinder, since it feels like im hitting the floor but the pedal isnt touching.

Not having abs, i think if i ever pressed my brakes that hard, the wheels would just lock.
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post #13 of 21 (permalink) Old 09-29-2008, 08:16 PM Thread Starter
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Replace the master cylinder, that is all.
That's not the problem. Trust me, try it on your car, it does the same thing.

Hell, a brand new BMW X3 sitting on the dealer's lot did the same thing. This is a design issue, not a defect.
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post #14 of 21 (permalink) Old 09-29-2008, 08:21 PM Thread Starter
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Originally Posted by linuxglobal View Post
ive actually never tried flooring the brake as my brakes kick in pretty quickly.

BUT my friends g35 has a similar issue that you are describing, you have to floor the brake to feel something. He Just had the brakes serviced, flushed, new pads and rotors front and rear and its still the same.

I wonder if ABS has anything to do with your issues? I dont see how it would but im just trying to look at it from all angles. I tried my brake after reading this and it wont touch the floor, it comes close to it but even if i press it really hard it never touches the floor as in feeling metal to metal contact. I didnt measure it.

You have to be losing pressure somewhere otherwise your system would explode with that much pressure applied to the brakes.

Engine off, my brake pedal will get very stiff after 1-2 pumps. Is there some sort of brake pump that runs off the engine ? There must be some hydraulic power, perhaps thats a flaw in the system?
I too, was highly suspicious of the ABS system. I thought the ABS accumulators / valves may somehow bypass the fluid pressure, if the pressure peaks above a certain point. However, I pulled the ABS fuse, and made no difference.

As I mentioned, my pedal is VERY stiff with the engine off, after 2 pumps, due to the master cylinder brace I installed (zero firewall deflection).

On a properly designed brake system, once the booster's power is all used up, the pedal stiffens up because your leg power is the only thing left to generate hydraulic pressure. Nothing would blow up because the leg power is relatively small compared to what's generated by the booster (easily in the 1000 lbs range).
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post #15 of 21 (permalink) Old 09-29-2008, 08:24 PM Thread Starter
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Originally Posted by 32Intrepid View Post
Wouldnt necessarily say its a problem, the car stops fine and always has. My dads truck does it too, its a dodge. Its just the way the brake system works. I get about an inch of movement before the brakes apply, and if I step much harder it will lock the tires and kick the ABS in -- that happens about half way to the floor, maybe alittle more.

Its hard to tell if its metal to metal contact or you are just at the maximum pressure of the hydraulic fluid. You can not compress fluid, so it may feel like its metal once you hit the limits of the system.

If your pedal is light and feels spongy, you may have a leak or air in the system. Then it will go all the way to the floor with ease. I have to put quite a bit of force into mine to make it go to the 2" from the floor.
I totally agree, this is not a problem at all; it just shows our cars do not have a performance oriented brake system, by far.

Under normal driving, the pedal is not spongy at all, since you're pressing nowhere nearly as hard to make it go to the floor. On a race track, or even "spirited" driving, it's a totally difference story. Our cars to do inspire the same confidence level as say, an E39 5-series.

And like I said before, I've verified this on quite a few other cars, even brand new, dealer lot cars do this, so definitely not an air issue.
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