I have noticed that the rear brakes on my 06 Impala SS are not working right. While I changed the struts on it I held the brakes and you can still turn the rear wheels. When I drive easy they seem to work but under heavy braking I get real bad nose down tail up action. The brakes are new front and rear. The calibers front and rear are new as well.
Just asking but why did you change all four calipers? I would try and bleed the system. Double check make sure all bleeder screws are at the top, maybe they were switched or put upside down? How does pedal feel? Could even be a bad master cylinder. Is it both rear wheels?
your car could be 60 years past warranty, if u take it in for example a window not staying up and they repair it and it falls back down a week later they are responsible and u take it back and have it repaired for free
2007 grand prix GXP-intake,exhaust,tune
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2008 Jeep wrangler unlimited- 2.5 inch rough country lift,33s,other random goodies.
if the pedal isnt spongy, then it sounds like the caliper's piston is hung up. It happens and even new calipers can be defective. The first generation W-bodies had defective rear brakes, I was replacing my rear brakes every 10 months and twice I received bad calipers where someone could be stepping on the brake pedal and I could still turn the wheel by hand.
Also, however I'm not 100% sure... you could might be able to have a firm brake pedal however the ABS pump might need to be bled as well.