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Old 11-26-2012, 07:16 PM   #1
MFE
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Default Brakes spongy unless released & quickly reapplied

On my recently purchased 2009 G9 GT with what I think are stock pads and rotors, I've noticed the pedal feels kind of spongy compared to most cars. The brakes work great, just don't like the pedal feel. THe other day I discovered that if I release the brakes and quickly reapply them, the pedal is high and firm like I'd expect them to be.

On every other car I've ever experienced, this is caused by one of two things: Air in the lines, or pad knockback, which is what happens when axle or bearing runout/endplay cause the pads to be pushed back into the calipers as the wheels rotate, and that slack then needs to be taken up before they really work, causing a long pedal travel.

I don't believe it's knockback, because on a car that doesn't have solid axles, it takes a lot of bearing runout to cause it, and I don't have any other symptoms of the sort.

That leaves air in the lines. I bled all 4 corners on Saturday, and the fluid looked good and I didn't see any significant air coming through the clear bleeder line. Nonetheless, I was suprised that the situation didn't improve at all.

SO...is this spongy pedal a normal characteristic of the G8? If not, any ideas where I should look next?
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Old 11-26-2012, 07:21 PM   #2
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You probably fixed this by bleeding but fluid with alot of moisture might cause this. How did the brake pads look? Still lots of material left?
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Old 11-26-2012, 07:26 PM   #3
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Yes, it's normal on these cars. Like you said, the brakes are good just a little too much play for my liking. Swapping pads will help. I'm doing a full upgrade in the spring once the stocks wear out.
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Old 11-27-2012, 10:57 AM   #4
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Assuming it's normal as many people have this complaint about GM cars when coming from other brands. While many people make the claim, GM brakes aren't spongy. Brakes of other brands are binary. They set them up to lock up your wheels with 0.000000000000000007mm of pedal travel. Why? I don't understand why people like that. Why would I want my brake pedal to have no usable travel? And why do so many people call brakes that actually utilize the pedal travel "spongy"? The opposite of "stiff" (as in a stiff pedal) is not "spongy."

You'll get used to it. It gives you more precision anyway.

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Old 11-27-2012, 12:01 PM   #5
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Following this thread...mine have started to do this also and with the same solution to get peddle feel back (release and quickly reapply)...Had the car since new and don't remember it doing it before even with the first two sets of pads...
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Old 11-27-2012, 12:06 PM   #6
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I also have this. I don't remember having it before I put new pads and rotors on the car two months ago. I didn't think much of it because the breaks do work fine. I just thought it was because I went with a cheaper solution than OEM.
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Old 11-27-2012, 12:40 PM   #7
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OEM brakes are great IMO. It's not a spongy feeling, just too much travel. After a couple of panic stops, I want more initial bite and better feel. That's why I'm upgrading. Not that the stocks are bad, but aftermarket is usually better. My .02 cents.
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Old 11-27-2012, 03:11 PM   #8
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The GT brakes are spongy, at least in my opinion (though I'm not the only one). It was something on my list that made me glad I got the GXP, which has greatly improved pedal feel over the GT.

To the best of my knowledge, the GXP and GT share the same brake lines, master cylinder, and ABS unit. The difference is the front Brembo calipers on the GXP. The downside is that they don't fit behind the GT 19" or 18" wheels, though I think they can be made to fit with spacers.

Glancing at your signature, if you ever plan to take your car out on a road course, I'm guessing Brembos would be an upgrade you could appreciate. You can get in touch with I12XLR8 here on the board for his experience running Brembos with his stock GT wheels.
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Old 11-27-2012, 04:00 PM   #9
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Quote:
Originally Posted by dandragonrage View Post
Assuming it's normal as many people have this complaint about GM cars when coming from other brands. While many people make the claim, GM brakes aren't spongy. Brakes of other brands are binary. They set them up to lock up your wheels with 0.000000000000000007mm of pedal travel. Why? I don't understand why people like that. Why would I want my brake pedal to have no usable travel? And why do so many people call brakes that actually utilize the pedal travel "spongy"? The opposite of "stiff" (as in a stiff pedal) is not "spongy."
And a stiff pedal doesn't necessarily correlate to higher effort. Making changes to any given braking system that reduce pedal effort always means you get longer pedal effort in the tradeoff, but that is not to say that short-travel systems, designed to be that way, are necessarily high effort. In most cases, they're not high effort, they're just short-travel.

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You'll get used to it. It gives you more precision anyway.
No, I won't, and the precision argument is not true. Unless we're talking air brakes, precision comes from brake pedal pressure modulation, not brake pedal travel modulation. And believe me, running a car on road courses for 10 years without ABS and autocrossing it for 5 years before that has taught me an awful lot about brake modulation with a high, firm pedal.
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Old 11-27-2012, 04:30 PM   #10
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Originally Posted by MFE View Post
No, I won't, and the precision argument is not true. Unless we're talking air brakes, precision comes from brake pedal pressure modulation, not brake pedal travel modulation. And believe me, running a car on road courses for 10 years without ABS and autocrossing it for 5 years before that has taught me an awful lot about brake modulation with a high, firm pedal.
It is true - you're looking at it the wrong way. Both travel and pressure matter. The point is that with longer travel, it takes less precision with the foot movements to get the point you want, because the pedal action is essentially "stretched out" so your movements are longer and require less precision. I can't really explain it that well. It's like taking a 16-bit audio signal but only using 1-2 bits of that, and leaving the other 14-15 bits there to do nothing. If you're trying to record music, it will sound like crap because of super high distortion because the recording didn't take advantage of the precision of using all 16 bits. That's probably the best way I can explain my point at this time.

I'm not saying that I am unable to drive a car with binary brakes that lock your wheels up when you even think about touching the brakes. I just don't see why anyone would like that. And I don't see what the problem is with the GT brake pedal travel. It's longer than with many other cars. And? Are you too short that you barely reach the pedal? Are you so weak that you can't press it fast enough?

My argument is that the longer pedal travel is easier to use, and that it still works fine for whatever purpose.

My mom's Accord - which I can drive just fine for the record - has WAY too 'immediate' a brake pedal that accomplishes absolutely nothing worthwhile. Not a single reason for that crap. I don't actually want the pedal to travel all the way to the floor or anything, but I don't want it to be anywhere near as immediate as it is on her car any more than I want the gas pedal to be that immediate. Though her car has the opposite problem with the gas pedal - it doesn't feel like it's connected to anything, because the car is too damn slow. haha
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Old 11-27-2012, 04:33 PM   #11
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You're each talking about two different things: travel and effort, and they're each distinct. Travel is the distance the pedal is able to move, and effort is the amount of force it takes to produce that travel.

MFE isn't talking about a pedal with no travel. He's talking specifically about the failure of the GT brake pedal to produce a roughly linear increase in resistance to travel - a roughly linear increase in effort, in otherwords - the further into the stroke you press the pedal.

So the issue isn't that the GT pedal travels too far. It doesn't. The issue is that it doesn't press back and, as such, gives you a rather vague and poor sense of how deep into the stroke you are.

Coming from a Mazda6, I test drove a G8 GT and immediately noticed the difference in pedal feel. Got to love Mazdas...
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Old 11-27-2012, 04:47 PM   #12
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Originally Posted by Eidolon View Post
So the issue isn't that the GT pedal travels too far. It doesn't. The issue is that it doesn't press back and, as such, gives you a rather vague and poor sense of how deep into the stroke you are.
I just can't duplicate that feeling. I dunno man. I've never once been unsure of what was going on with my brakes.

When comparing, to me - well, I will give another audio analogy. You know how many people tend to confuse volume with sound quality, i.e. if you A/B them the same signal at slightly different volumes, most people will assume the louder signal to sound better? You turned up the volume with your Mazda 6, and in the G8 you turned it back down. It may seem lower quality, but it's just different.

That's what it's like to me, anyway.

Anyway, I have probably explained what I meant well enough now, so I'll leave the discussion alone.

Edit: Oh, and one more thing. Don't think you can change the pedal travel notably by doing simple stuff like the stainless braided brake hoses that many people like to do. You'll need to really dive into the brake system if you want to really change it. Assuming we're still talking about a car that MFE just doesn't like the brake pedal feel of (as opposed to it truly having air in the lines).
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Old 11-27-2012, 05:07 PM   #13
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Modulation does not have to come from long pedal travel, and "short travel" does not equate to "binary brakes" unless the driver is incapable of modulating how much pressure they apply to the pedal. If that's the case, they're probably a paraplegic using hand controls anyway, and the argument is moot.

I like to modulate pressure, not travel, not only because it feels better to me, but because I'm less likely to accidentally catch the gas while braking hard with such a long pedal stroke. If this is considered normal for these cars then I'll have to add it to the very short list of things I don't like about it. I don't *like* a pedal that feels like the brakes need bleeding, and this is one of very few cars I've encountered in almost 30 years of driving that feel that way.
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Old 11-27-2012, 05:13 PM   #14
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Quote:
Originally Posted by Eidolon View Post
The GT brakes are spongy, at least in my opinion (though I'm not the only one).
To quote the source:

Quote:
Originally Posted by Engineering Editor Jason Kavanagh
For all the things done right in the 2008 Pontiac G8, the "Buick-circa-1988" squooshy brake pedal is made that much more incongruous. The bite over the initial inch or so of pedal travel is largely nonexistent. It's like stepping on a Care Bear.
Exactly what I'm talking about.

I just think it's really strange that releasing and immediately re-applying the brake makes them feel like they should. I'm deeply familiar with how braking systems and their boosters work, but that's a head-scratcher to me.
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Old 11-27-2012, 05:14 PM   #15
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Quote:
Originally Posted by dandragonrage View Post
I just can't duplicate that feeling. I dunno man. I've never once been unsure of what was going on with my brakes.

When comparing, to me - well, I will give another audio analogy. You know how many people tend to confuse volume with sound quality, i.e. if you A/B them the same signal at slightly different volumes, most people will assume the louder signal to sound better? You turned up the volume with your Mazda 6, and in the G8 you turned it back down. It may seem lower quality, but it's just different.
Yup, I know exactly what you're talking about. Sound cards in computers often pull the trick of bumping their output volume when you enable any processing to create the perception that quality has been improved. Turn the volume back down to compensate, however, and the difference is usually either unnoticeable or actually undesirable. Not quite sure that the analogy fits here, though...

I think a lot of it is just what you got used to in previous cars. The Mazda's pedal effort was honestly a bit higher than I would have liked, but the effort built up nicely as I applied pressure. It made it easy to modulate by pressure.

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Originally Posted by MFE View Post
I like to modulate pressure, not travel, not only because it feels better to me, but because I'm less likely to accidentally catch the gas while braking hard with such a long pedal stroke. If this is considered normal for these cars then I'll have to add it to the very short list of things I don't like about it. I don't *like* a pedal that feels like the brakes need bleeding, and this is one of very few cars I've encountered in almost 30 years of driving that feel that way.
Ditto on modulating by pressure. I'd see if you can find a GXP owner nearby who will let you take their car for a short spin. If you like what you feel, you have a known-good upgrade path that should pick this nit off your list.
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Old 11-27-2012, 05:20 PM   #16
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I just think it's really strange that releasing and immediately re-applying the brake makes them feel like they should. I'm deeply familiar with how braking systems and their boosters work, but that's a head-scratcher to me.
If I'm right about the differences between the GT and GXP, then it all comes down to the dual-piston sliding/floating calipers at the front of the GT. Perhaps they somehow back off the rotor after release? And I mean more than just the fractions of a millimeter necessary to free the rotor from the pads.

If Edmunds can still be considered a good source, here's another quote from a GXP follow-up test:
Quote:
Originally Posted by Edmunds.com, Dan Edmunds
The GXP's stopping distance from 60 mph comes in at 110 feet — the same result as the G8 GT with the same tires, but smaller brakes. The benefit from the new brake package expresses itself as increased fade resistance after numerous hard stops, and excellent pedal feel.
Not the same author as the source of the previous post, though, so I guess it should be taken with a grain of salt. But the original G8 GT test also had this quote from a different author:
Quote:
Originally Posted by Edmunds.com, Scott Oldham
The G8 GT's four-wheel disc brakes are also worthy. They help produce a stopping distance from 60 mph of just 109 feet with excellent fade resistance, and they can hang with the best from Germany. But they're also activated by a soft pedal that provides little feel. It's the one real dynamic flaw in an otherwise impressive package.
I'm a broken record. But if you do want to fix it, it can be done.
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Old 11-27-2012, 06:14 PM   #17
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GM stock pad tend to be very quiet and very clean. The GT has no brake dust, but the down fall is a spongy pedal. You could get a set of nice dust stoptech pads, hawk HP (not HPS) or something better, with some nice black wheel dust, and the pedal will feel better. Actually stock Brembo/GXP pads feel stronger and less squishy then most other pads I have ever had.

I have a GXP and the stock Brembo pads are very dusty and firm feeling. When switched to Stoptech front pads, they were almost as dusty, but initial bite and the firm pedal were somewhat lost. I think the GM-Brembo pads are Ferrodo... not sure what model though.

I hate squishy pads.
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Old 11-27-2012, 06:43 PM   #18
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I tend to agree with the pressure modulation folks on this one. I prefer to apply enough pressure to get the initial bite (how much bite is a discussion about pad compounds) and then modulate the pressure to get the desired braking. I tend not to like lots of travel in the peddle before the initial bite.

When I first drove the GT the brakes were the best I'd driven, but looking back at how I drove compared to now (with the aftermarket brakes) it was definitely different. The stock brakes required far more peddle travel to get the initial braking I desired, but then did a good job at that point. Not having driving anything with a "firm peddle" I didn't know any different... going back now would feel very "squishy".

Back to pad composition for a moment... I noticed with the same brakes a dramatic difference in initial bite from one pad to another. When installing a "track" pad I had to become much more gentile on the brake peddle using the same amount of travel/pressure to avoid lockup. I could install a pad with less initial bite and reduce the tendency for the car to lockup with minimal peddle travel, but that's not what I'm after.

Quote:
Originally Posted by dandragonrage View Post
Why would I want my brake pedal to have no usable travel? ...It gives you more precision anyway
I would prefer to have more the usable travel after the point of initial bite, not before. Basically, I don't want to have a linear brake peddle response. I would much rather use the precision associated with travel at higher braking levels.

When I want to use the brakes on-track, I want them to work immediately (0% to 50% braking almost instantly)... I don't want to need to move the peddle 50% to the floor. After the point of initial bite I want to use the peddle travel to precisely modulate my braking.

Just to spark some more debate... wouldn't having a peddle with minimal travel on the street allow for additional travel (before "bottoming-out") in high performance (aka. track) conditions? Hot/sticky tires will take much more braking before locking... but using that setup in the rain would be quite difficult...

Personally, I'd rather "baby" the brakes on the street (when the speeds are low and I can more easily brake for longer distances) to get the performance I want while driving in a more "spirited" manner and on-track.

-Todd...
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Old 11-27-2012, 07:19 PM   #19
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Quote:
Originally Posted by Jeff92se View Post
You probably fixed this by bleeding but fluid with alot of moisture might cause this.
I figure moisture wouldn't be an issue until the fluid got quite hot (air resulting from the lower boiling point of the moisture-rich fluid).

Quote:
Originally Posted by dandragonrage View Post
Don't think you can change the pedal travel notably by doing simple stuff like the stainless braided brake hoses that many people like to do.
Stainless lines might help the feel a little. While it might not solve the whole problem, it likely wouldn't hurt anything.

Quote:
Originally Posted by dandragonrage View Post
It's like taking a 16-bit audio signal but only using 1-2 bits of that, and leaving the other 14-15 bits there to do nothing. If you're trying to record music, it will sound like crap because of super high distortion because the recording didn't take advantage of the precision of using all 16 bits.
To use an audio/bit example... think about the frequency range. If I'm recording something with minimal base, but lots of distinct treble tones (ie. a flue solo)… I'd rather use my bits of resolution to focus on the treble than full spectrum of frequencies. Yes, there would be additional distortion at the lower frequencies… but I'm sacrificing that for the increased resolution in the more desirable range.

Applied to the brakes… I'd rather have less resolution at lower braking levels (0%-25%) if it results in greater resolution… and greater precision… at higher braking levels (25%-100%).

Quote:
Originally Posted by MFE View Post
"short travel" does not equate to "binary brakes" unless the driver is incapable of modulating how much pressure they apply to the pedal.
Agreed 100%. When I was looking into brake pads for the track I was a little surprised to see "for experienced drivers" listed at a caution on some pads. After reading more about initial bite it became more obvious... the high initial bite produces a greater stopping force, but it takes an experienced driver to properly modulate the pressures. Based on your experience, and description of the current feeling, it sounds like you're more comfortable with the greater stopping force by a braking setup with high initial bite with minimal initial peddle travel (as I would describe as having a "firm" peddle) than one with less initial bite and more peddle travel (as I would describe as having a "soft" or "squishy" peddle).

Quote:
Originally Posted by MFE View Post
I just think it's really strange that releasing and immediately re-applying the brake makes them feel like they should. I'm deeply familiar with how braking systems and their boosters work, but that's a head-scratcher to me.
Agreed… it's almost like you're having to rebuild pressure. Almost like a "slow leak" (I don't know if that's even possible though) more so than lines, fluid, etc.

I wonder if you flushed your fluid and changed to stainless lines if that would improve things enough? Then again, at that point you're part way into the labor of swapping calipers.

-Todd...
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Old 11-28-2012, 10:13 AM   #20
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I agree the GT brakes feel rather spongy and provide poor modulation. Even with new brake pads, rotors and fluid flush. Coming to a quick stop often ends up my head jerking forwarding from applying too much pressure. They are just tricky to modulate.

I find my GTO brakes are less spongy and easier to modulate.

As far as stopping power is concerned I don't know which are more powerful, the GT or the GTO brakes.
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