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Discussion Starter · #1 ·
I have a 2012 chevy impala and I cannot figure out the brakes. I recently replaced master cylinder and have bleed the brakes several times. I cannot get it to build and maintain brake pressure. it's not leaking fluid and brake lines and calipers look OK. Has anyone ran into this issue? Or does anyone have an idea of what it could be?
 

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I have a 2012 chevy impala and I cannot figure out the brakes. I recently replaced master cylinder and have bleed the brakes several times. I cannot get it to build and maintain brake pressure. it's not leaking fluid and brake lines and calipers look OK. Has anyone ran into this issue? Or does anyone have an idea of what it could be?


On vehicles with an ABS system, a special controller (such as the GM Tech 2) must be used to aid in brake system bleeding - to cycle the ABS control unit shutter valves, to eliminate all air in the system.
 

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Discussion Starter · #3 ·
On vehicles with an ABS system, a special controller (such as the GM Tech 2) must be used to aid in brake system bleeding - to cycle the ABS control unit shutter valves, to eliminate all air in the system.
I used one of the controllers when bleeding. I even used a power bleeder. Still don't have brakes. I'm thinking the replacement master cylinder is bad. Also thank you for the reply! :)
 

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2004 Impala LS 3.8L (~130k miles)
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Did you bench-bleed the MC prior to installation?
It's possible to have a bad new part....factories are not perfect. But do note that the symptoms are strongly suggesting air in the brake system somewhere.....
 

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Discussion Starter · #5 ·
Yes! I took it to a friend has a mechanic shop. We bench bled the MC and bled the brake lines. We went through the proper steps for bleeding. Still can't find any leaks or any reason why the brakes would still be spongy
 

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2004 Impala LS 3.8L (~130k miles)
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As suggested by 1999 White C5 Coupe, there could still be air in the ABS unit....they are notoriously difficult to bleed if ever they get air inside. It might require a special GM tool and tech to perform.
Other than that, the MC itself could be bad even though it's new.....
 

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I’ve dealt with this before with my old Tahoe. Just use the scab tool to perform at least two more cycles of the automated power bleed. I have a Tech 2 and it has me go around in a circle to each caliper to crack open a bleed screw while the driver carefully pumps the brake pedal.
 

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I went through the bleed assist procedures where you use a scanner to cycle each individual abs pump. I've done itultiple times with no luck and have probably ran a gallon of brake fluid through the lines. I still don't have any brakes. There are still no leaks and I've put another master cylinder in it with no luck. Idk if it could be a brake booster issue or what...
 
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