I am working on an 08 cobalt SS that i just bought off a guy "as is" it didnt run, and had no resistance at the brake pedal.

Well i got the engine running like a top... (it was an issue with the intercooler plumbing and a detached vac line..)

but after bleeding the brakes i still cant seem to get much resistance at the pedal. before it had nothing at all. now it build pressure as you pump it, but slowly looses pressure.
it isnt loosing any fluid anywhere... reservoir is full and stays that way. bled all 4 corners and dont seem to be getting any bubbles or air.

any idea what this could be? could the abs unit be causing this? possibly a bad master cylinder? any ideas?

any suggestions on what to do from here?

there are no fluid leaks.. everything is bone dry... i have bled the heck out of it so i doubt it is air... what else could it be?

 

May be the brake booster. Idk.

 

If there are no external leaks, prime suspect would be the master cylinder in my experience. Either it is pooched or in need of bleeding - guessing since you bled the whole system that won't be the case.
Should be able to get a used one from the bone yard, may be available from an aftermarket (NAPA, Autozone, Pep Boys, etc) supplier. Even from the dealer should not be more than a couple hundred bucks.

ABS unit is a possibility - not sure on the 'Balt but some cars require a special tool to "activate" the abs unit so it can be bled, like I say I'm not sure if this applies on the 'Balt.

 

just FYI... for those of you with 08+ cobalts...

the brembo front calipers have 2 bleeders per caliper... you need to bleed them both... inners first then outters....

that was my whole problem. brakes work fine after bleeding both sides of both rotors.