Brakes feeling soft

[Fingers]

K, i've almost gotten to the point of getting my vibe on the road. (been sitting for 2 years). 2003 Vibe GT 6MTI am getting a soft/spongy brake feel with the car turned on. When the car is off, and I pump the brakes, they become firm, with a nice feel. When I turn the car on, and apply the brakes gradually, i can essentially hit the floor with the pedal. If I stomp on it, i do feel some pressure, but it's not at all what you'd expect out of a well-working braking system.I've done the following:-had the rotors turned-bled the system THOROUGHLY. Got some air out, braking improved marginally, still very poorI suspect the following:-leak from the left front caliper... i found some fluid inside the wheel, but i may have spilt some from the hose i was using to bleed the brakes with. -master cylinder bypassing on itself. What are likely causes for a car that's been sitting this long?And please, if you've never worked on a brake system, or you're under the age of 20, save your breath. It's not my intent to be discourteous, I just find alot of misinformation on car boards.

[kevera]

The rubber dries out(dry rot)I would probably replace both sides.Did you also check the wheel cylinder on the backs.

[Fingers]

Exactly what rubber are you referring to? And this is an 03 GT, so it's four wheel disc. The back calipers definitely aren't leaking, because i spent most of my time working/bleeding them. The front left, i'm not 100% positive.

[joatmon]

I had the same problem on a non-Vibe last weekend. WIth the engine not running, the pedal was really firm, with the engine running it would push all the way to the floor. Fascinated by this phenomenon, I pushed it all the way to the floor several times. The faulty wheel slave cylinder became obvious by a puddle of brake fluid.Some cars with ABS have convoluted procedures and special equipment to bleed the entire system,but I couldn't find anything in the book about special bleeding for ABS equipped Vibes/Matrixes. If you have properly bled the brakes, and pushing the pedal to the floor repeatedly doesn't give you a puddle somewhere, then I'd think it would have to be the master cylinder. Here is a PDF of the master cylinder overhaul. Not sure how much help it would be, I'd be torn between rebuild and replace, since I wouldn't trust myself to rebuild it right. In a car, being able to stop is more important than being able to go. When you do get it figured out, let us know the cause and cure

Attached files w040001.pdf (115 KB) 

[Sublimewind]

You say you bled the system, but, did you FLUSH the system? I guess it's possible you could have some condensation in the lines from sitting. Seems you need to look at that front left to be 100% on it... get someone to pump them for you and inspect... Oh and i'm over 20 AND have worked on brakes... BTW

[Fingers]

Condensation/brake fluid's affinity for water was my first suspicion, and I did flush it thoroughly. Here's the thing though, that can't be it. Water is not compressable until it becomes a gas (boils)... so even if it were water, it still wouldn't explain why the pedal feel isnt there.I'm leaning strongly towards replacing the master. We'll see.

[Fingers]

No fluid leaking out the front left caliper, unfortunately. Leaning strongly towards master cylinder. $50 at a junk yard, can't find a new one, dealer only. Guess i'll give it a shot.

[joatmon]

oh well, at least you can do the work yourself. Think of the money you are saving, and all the fun you are having I hope that fixes it.So how come it has been sitting idle for two years?

[Fingers]

I still haven't gotten the car on the road for various reasons (travel, move, etc). The last time I worked on it, I replaced the master cylinder, bled the entire thing MANY times, with the car on and off, still same problemI made and installed blockoff lines for the master, and tested it with the engine on and off... very firm brake pedal feel -- master cylinder eliminated.I checked all the rubber hoses. None expand. Hoses eliminated.I serviced all the brake calipers and machined the rotors. No leaks found. Calipers eliminated.Very few things left. Perhaps I've got some stubborn air still in the system... i'm doubtful, but i don't have many options left! Tomorrow, I'm going to slap the wheels back on, and go around the block locking up all four wheels in the snow. Hopefully, if the air is stuck in the ABS pump, it will be loosened. Past that, I will be blocking off one wheel at a time at the ABS pump to see if I can troubleshoot the system by dividing it in two. Ideas? Much appreciated.