Brake Pedal is erratic

[Jkust]

All, before I changed my rear brakes and rotors on my 9-7, the pedal would sometimes go too far down and other times be fine. I thought it was due to the piston traveling too far as the rears were down to metal. I put on new rear pads and rotors and verified the fronts were new as the dealer indicated. The pedal situation never changed. Basically it is a crap shoot as to if the pedal will be nice and hard and the brakes will grip as intended or the pedal will go too far down causing you to need to pump them to get full breaking power and the cycle starts all over.

Given the pedal situation wasn't related to the pads being worn though the timing seemed to indicate they were related what do you think?
Possibly a master cylinder? I didn't bleed the brakes when I did the rears but I'm a bit confused as to what this could be. Sometimes the brakes will be perfect and others require pumping on the same 25 mile drive? When they work they stop great and when they don't the stopping power is cut down.

 

[HARDTRAILZ]

Rubber brake lines swelling or having a bubble spot possibly.

 

[BRomanJr]

All, before I changed my rear brakes and rotors on my 9-7, the pedal would sometimes go too far down and other times be fine. I thought it was due to the piston traveling too far as the rears were down to metal. I put on new rear pads and rotors and verified the fronts were new as the dealer indicated. The pedal situation never changed. Basically it is a crap shoot as to if the pedal will be nice and hard and the brakes will grip as intended or the pedal will go too far down causing you to need to pump them to get full breaking power and the cycle starts all over.

Given the pedal situation wasn't related to the pads being worn though the timing seemed to indicate they were related what do you think?
Possibly a master cylinder? I didn't bleed the brakes when I did the rears but I'm a bit confused as to what this could be. Sometimes the brakes will be perfect and others require pumping on the same 25 mile drive? When they work they stop great and when they don't the stopping power is cut down.

I'm having a similar problem, but possibly not as severe as yours. Mine would always stop better on the second pump, so I figured it had air and I would need to bleed them, not sure front or rear though. After many miles of putting up with it it appears mostly improved after my last 3000 mile trip, not sure what to think anymore.

Many discussions on here and the OS about lousy brakes and long pedal travel. Some fixed with standard bleeding and some required bleeding the ABS unit using a Tech II or similar capable tool. Not many have reported back (IMO) the fixes they used.

Sounds like yours is air, but may need to bleed the ABS with a capable OBDII tool, then bleed each wheel using the bleeders.

 

[Jkust]

I'm having a similar problem, but possibly not as severe as yours. Mine would always stop better on the second pump, so I figured it had air and I would need to bleed them, not sure front or rear though. After many miles of putting up with it it appears mostly improved after my last 3000 mile trip, not sure what to think anymore.

Many discussions on here and the OS about lousy brakes and long pedal travel. Some fixed with standard bleeding and some required bleeding the ABS unit using a Tech II or similar capable tool. Not many have reported back (IMO) the fixes they used.

Sounds like yours is air, but may need to bleed the ABS with a capable OBDII tool, then bleed each wheel using the bleeders.

Interesting. I didn't have any issues with mine right up until the rear brakes started indicating and got worse as the brakes got more and more worn down. You'd think the pedal and the worn brakes were directly related. In other words if there is air in there, how did it get there?

 

[Wooluf1952]

Brake fluid absorbs moisture. Under hard braking the moisture can boil causing steam and air bubbles. It's one of the reasons the fluid should be changed.
I've heard change intervals any where from yearly to every five years to just every time a brake job is done.

 

[Jkust]

Forgot to mention, when I changed the pads/rotors, I had to top off the brake fluid resoivoir which should never need to be done.

 

[BRomanJr]

Forgot to mention, when I changed the pads/rotors, I had to top off the brake fluid resoivoir which should never need to be done.

Usually the level goes down as the pads wear and if you push back the pistons when installing new pads (not usually recommended), the level goes back up.

Not sure how your level went down unless you opened bleeders when pushing back pistons and got air in.

EDIT:
On second thought, if the pads were worn down enough, the piston could have been over extended and introduced air.

The fix for both of those is a good bleeding at both calipers.

 

[Jkust]

Usually the level goes down as the pads wear and if you push back the pistons when installing new pads (not usually recommended), the level goes back up.

Not sure how your level went down unless you opened bleeders when pushing back pistons and got air in.

EDIT:
On second thought, if the pads were worn down enough, the piston could have been over extended and introduced air.

The fix for both of those is a good bleeding at both calipers.

Ok if the piston can overextent and let air into the system, that would make sense as I didn't open the bleaders. The overextension got worse as the pads got to the metal and that would make sense. I wasn't aware air could enter into the system other than through the bleaders but I suppose the fluid being low even after pusing back the pistons is still a mystery. I'm not really equipped to blead the system or I would have done it.

 

[Lima Tango]

Ok if the piston can overextent and let air into the system, that would make sense as I didn't open the bleaders. The overextension got worse as the pads got to the metal and that would make sense. I wasn't aware air could enter into the system other than through the bleaders but I suppose the fluid being low even after pusing back the pistons is still a mystery. I'm not really equipped to blead the system or I would have done it.

All you need to bleed them the manual way is an old soda bottle, short length of clear hose sized to fit over the valve, an assistant to pump the brakes for you, and an end wrench. Flushing completely takes awhile but you can do it that simple as well. This is obviously the first thing to try as it's easy and low cost, as opposed to paying for ABS service or replacing the MC.

 

[Jkust]

All you need to bleed them the manual way is an old soda bottle, short length of clear hose sized to fit over the valve, an assistant to pump the brakes for you, and an end wrench. Flushing completely takes awhile but you can do it that simple as well. This is obviously the first thing to try as it's easy and low cost, as opposed to paying for ABS service or replacing the MC.

Thanks, the more I'm dealing with this the more it makes sense that there must be air in the system.

 

[Mooseman]

Try bleeding them yourself first but if the problem persists, it could be air trapped in the ABS module and to properly bleed that, it will take a trip to the dealer (and $$$) to hook up a Tech2 to cycle the ABS to get all the air out.

 

[Jkust]

Try bleeding them yourself first but if the problem persists, it could be air trapped in the ABS module and to properly bleed that, it will take a trip to the dealer (and $$$) to hook up a Tech2 to cycle the ABS to get all the air out.

Ok but I don't like to see $$$ and dealer in any sentence.