Only the top two pistons move when the brakes are applied

2006 CHEVROLET TRAILBLAZER
160,000 MILES • 4.2L • 6 CYL • 4WD • AUTOMATIC
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BEHINDTHE8BALL
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The front brake calipers only the top pistons are pushing out the brake lines have been replaced. The front left brake calipers replaced. Still the same result only the top two pistons move when the brakes are applied. They were bled properly I started from the right rear went to the left rear front right front left. I have plenty of brake pedal, no sponginess, doesn't stick. Just the pistons won't move together on either side and as I said the front left driver side is brand new.
May 12, 2021 at 4:55 AM
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ASEMASTER6371
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Good morning,

I attached the procedure for you for replacing the calipers. Both pistons should move together. If only 1 piston moves, then the other is seized.

https://www.2carpros.com/articles/brake-caliper-replacement

Make sure you flush the system of all fluid and replace it with new fluid.

https://www.2carpros.com/articles/how-to-bleed-or-flush-a-car-brake-system

Roy
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May 12, 2021 at 6:10 AM
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BEHINDTHE8BALL
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I didn't realize I can respond to you sorry thank you for getting back to me I have replaced the front left caliper it's brand new and it's having the same exact issue the bottom piston does not work only the top piston push this out when I'm pumping the brakes it's got new brake lines a new front left caliper still didn't solve the issue.
May 12, 2021 at 8:51 AM
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ASEMASTER6371
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Okay, did you use or clean the slider pins that are identified in the illustrations I posted?

If the slider is seized or dirty, one of the pistons will not move.

Roy
May 12, 2021 at 9:00 AM