G Speed

So... after taking my car to the track.... the next morning I go to start up my car...

When I press my brake pedal the moment it starts.. it makes an odd "crunch sound" I can kind of feel it in the pedal too... almost like resistance, like im pumping air out of the system....

After 1 or 2 pumps... it goes away...and braking is fine...

I'm a little low on fluid... but no warning messages nothing

Pontiac.G5

check your brake fluid

turbaltss

Strip or road course? bleed your brakes if was a road course all the heat from hard braking causes brake fluid to break down.

Gestapo007

iTrader: (2)

i dont know **** about brakes, but if I was having a problem with brakes, n i knew i was low on fluid, I would first fill my brake fluid to help narrow it down. Just saying

G Speed

road course... it was in the rain so I was on them alot more then usual...

It's in between min and max right now

Permafried-

Hmm, does it feel like your ABS is engaging while you're sitting still? When you say 1 or 2 pumps and then it goes away, does it go away for good, or do you feel it under normal driving conditions as well?

G Speed

Well I geuss you could take that abs feeling.... make the feeling 10X harsher or harder.. "hard to describe".... but once that feeling is gone.. the braking is fine..

It's like something is blocking a line... when I start the car up, I have to almost push it out with the brake pedal... like little sacks of air exploding...

Permafried-

There's no evidence that your fluid started boiling when tracking the car is there? In other words, is your fluid substantially lower now than it was before you took it out for the day (obviously taking into account you would have sluffed some pad off in the process)? Does it look like the bleeders (front or rear) were "wheeping"?

I highly doubt anything is blocking the line but if it DID start to reach boiling point you MIGHT (big might) have developed tiny air bubbles in the lines that settle out when the system is no longer pressurized. Out of curiosity, try starting your car, do not touch the brakes then shut it off, unload the sysetm (brake down to floor, back up, try once more until the pedal doesn't want to move anymore) and restart it immediately after and try again. I've never done this myself but you might want to sample your brake fluid for water content (since you were tracking in the rain) to see what % of the fluid is water as well.

If it persists you may want to remove the pads and inspect the brake system just to be sure nothing is hung up and perhaps check your brake lines to make sure nothing is slightly pinched (doubtful on this one). Also, take the vehicle out (make damn sure your brakes are working well first ) and try some moderate stops (to complete stop) from 35mph and then a couple harder stops (hit ABS if you want) from 50mph to see if this helps.

Diagnosing brake issues can be a severe pain in the ass so I might seem like I'm grabbing at straws but you're looking process of elimination if it doesn't correct itself and best to start smiple and work your way through it.

G Speed

There's no evidence that your fluid started boiling when tracking the car is there? In other words, is your fluid substantially lower now than it was before you took it out for the day (obviously taking into account you would have sluffed some pad off in the process)? Does it look like the bleeders (front or rear) were "wheeping"?

No wheeping from the brakes, fluid is a tad bit lower

I highly doubt anything is blocking the line but if it DID start to reach boiling point you MIGHT (big might) have developed tiny air bubbles in the lines that settle out when the system is no longer pressurized. Out of curiosity, try starting your car, do not touch the brakes then shut it off, unload the sysetm (brake down to floor, back up, try once more until the pedal doesn't want to move anymore) and restart it immediately after and try again. I've never done this myself but you might want to sample your brake fluid for water content (since you were tracking in the rain) to see what % of the fluid is water as well.

Will go outside and try it now

If it persists you may want to remove the pads and inspect the brake system just to be sure nothing is hung up and perhaps check your brake lines to make sure nothing is slightly pinched (doubtful on this one). Also, take the vehicle out (make damn sure your brakes are working well first ) and try some moderate stops (to complete stop) from 35mph and then a couple harder stops (hit ABS if you want) from 50mph to see if this helps.

Diagnosing brake issues can be a severe pain in the ass so I might seem like I'm grabbing at straws but you're looking process of elimination if it doesn't correct itself and best to start smiple and work your way through it.

and the brakes do work fine... other than that odd "crunch"...abs still works etc..
think of it as putting a big large apple behind the pedal... and crushing it...

Permafried-

Air in the lines tends to make the pedal feel "squishy" since compressing the air takes more force than compressing the fluid. I'm just trying to figure out how you could have gotten air in the lines without opening the system

G Speed

okay went outside and did what you said... didn't hear that crunching sound... I just find it hard to have destroyed my brake fluid in 1 track session in the rain.. so no 150kph stops.... and 18000km highway miles?

Unless GM stuff is garbage?

I mean I could just go to the dealership, but I hate that place it's like going to a hospital... and they probably wouldn't even be able to replicate the problem or tell me it's normal

PrincessTurbo

They used the Brembo name on an economy car,

Have you not read about rear rotor and pad issues? With 18000 miles not km my rear pads and rotors were toast .. pretty sure it isn't the brake fluid .. have you ever had brake fluid go bad on you before it gels up. You would know if they gel. Braking is extremely difficult, it wouldn't be at start up you noticed it.

Just take it in but I doubt they will give you any type of warranty on pads and rotors.

Just get R1 Concepts stuff with Hawk pads, better yet keep the stock front pads if they are good and get just rears and rotors all the way around... The stock rotors do not dissipate heat or rain on track like conditions.

Why would you race in wet conditions anyway ? The front brembo's have a bleeder valve that is real easy to get at .

http://www.ehow.com/how_5095410_blee...bo-brakes.html


I would just take it in man and expect no warranty on wearable items ..

G Speed

Ummm..

1. Blanks are better then slotted and drilled
2. Why wouldn't I race in wet conditions?

SSlobalt

I get this crunch sound everytime I'm on the brakes and end up turning into an inclined drive. I assume that's the ABS, so it's probably the same for yours. I don't know why it did it, but unless it continues, I wouldn't worry about it.

Permafried-

If I pump mine 2 or 3 times sitting idle I will get the noise, but it sounds like his is slightly different. Based on the tests he ran, my guess is it is really nothing to be concerned with but it's really tough to say since brakes tend to be a "by feel" type of diagnosis.

exiged

Please elaborate, especially for slotted. . . .

PrincessTurbo

Besides maybe slightly more pad wear and possible cracking which R1 does the best job at ensuring it doesn't..
https://www.cobaltss.net/forums/show...light=Concepts


In your case the slotted rotors are for gassing, when the pads reach their operating temps or higher they start to gas or breakdown and the slots are there to allow the gas to escape. So the people who say that drilled and slotted are useless haven't done the comparison on real track brakes. Maybe if this was an LS .. The Brembo's brake and behave a little different then your average caliper. So heat dissipation is the key factor here , Warp your "blanks" then tell me they aren't better Heat is what kills fluid. I live at 6000 ft boiling temps occur a LOT faster here ...

The materials R1's use will last a lot longer too, you are braking under , Wet , Slick , conditions around corners having to use the brake's even more and you ask why wouldn't you race in the rain . simple answer is traction ...

I race a super late model ...

LOL probably read that on a civic forum or some place where they don't have brakes with enough piston pressure in the caliper to even warp the rotor or cause enough heat to make a difference ...

Fact is the best drilled slotted rotors are cast with the holes in them, Ferrari does this but as long as the holes are chaffed and you use ceramic pads the rotors will last a lot longer and will give the pads a more even wear period creating less stress on the system overall

Stock front pads are fine they just give of lots of dust.....

Wangspeed

iTrader: (2)

PrincessTurbo, do you do anything other than bitch about this car?

G Speed, the front brakes on this car are great. There are many of us that have beaten them up on track, and they're better than STI or Evo brakes. I've owned both of those. The front pads are quite good. I'd pull the front pads to see if there's some crude preventing the pads from moving back and forth easily. If you can't find anything there, just bleed the fronts and see if that helps.

I'm gonna take a bet that one of the anti squeal shims is out of place, or that something weird happened like the backing plate or pad is damaged due to too much thermal changes, like an extraordinary amount of water on the hot pads/rotors.

Amen.

Permafried-

Based on the design of our front brakes I'd be more inclined to wonder if something is trapped on the rears since the fronts are only suspended by the pins and spring. Even after a full winter of driving my pins were clean, my rears were so gunked up it was ridiculous. I agree though taking them apart one at a time, inspecting them for damage, build-up, etc. and cleaning/lubricating everything. If that's not the problem it certainly can't hurt .

Wangspeed

iTrader: (2)

Agreed. Since the rears don't get that hot, I used suspension lube, which is sticky nasty waterproof teflon stuff. It'll last longer than anti-seize or cheap brake lube.

Permafried-

I went with a synthetic brake lubricant with similar properties to what you used mind you my car doesn't see track days so who knows how it would hold up there. Sticky, thick, waterproof (couldn't even get it off my hands ) and so far it is doing the trick for the DDing I do .

G Speed

1. got back from GM.. I live in a small town, so they are friendly.. foreman came out to check the pedal feel.. he told me it was perfect... and he was gonna check the start up procedure of the car...

He told me, that it's the abs solenoid testing it self.. so that's good to know

2. It's funny.. how F1 cars use blank rotors.... cause you know all the "GASES" lol

3. They are replacing my rear rotors & pads I just have to pay $99 for full brake service which they will do also

PrincessTurbo

Open wheel cars don't need duct work in the front to cool the rotors or pads because they are "open wheel"


Last time I checked a Cobalt wasn't an F1 car.

Funny they are replacing your rears , just like I said . You are still paying out your pocket

G Speed

Yea... I get there open wheel... just stop believing what everyone is telling you about slotted and drilled, for brakes you want to most surface area possible.... slotted and drilled don't give you that, now I know your next argument is going to be about the slotted and drilled how they cool down the brakes.. well the blanks, have more surface area = large area to dissipate the heat...

I don't mind for paying out my pocket for the rears, I do take the car to the track... and I do have 18000km's on the car... so for $100 that's a steal...

cubaniche

iTrader: (1)

So is this 'ABS testing' going to go away? I never felt the pedal doing this 'crunching' thing under normal operation or startup like yourself. So its weird he said it was normal.

I have R1 slotted on all four corners. Rear discs are crap from the factory. Too much of an agressive pad for the GM blanks causes scoring, especially the inner rear drivers side disc. A lot of us that have R1's in the back with HPS pads have proven that this combo works and there is no more scoring going on and they operate like they should.

Front discs and pads are great! But I replaced them too because I wanted better wet performance and I wanted the car to match. It does brake better after a wash and in the rain. No one is saying to go spend money on them if you dont want to, but they are better in the long run.....IMO If slotted is not your cup of tea, well, R1 does make Premium blanks too.

Glad your getting your rears replaced though.