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Old 08-21-2011, 05:00 PM   #1
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Default Rear Caliper Piston Won't Retract

I'm changing the pads and rotors on a 2000, A-6, 4.2L. The rear caliper piston won't retract when trying to run it back into the caliper housing with the disc brake piston tool. Same problem on both sides. The piston just seems to spin when I push and ratchet it inward. Sometimes it feels like the piston is binding up as it turns, rest of the time it turns freely. The piston appears to have right hand threats. I tried opening the bleeder valve to release pressure. Also tried to retract the piston using a C-clamp. The piston was well extended as the pad was worn down to approx. 1/8".

What am I missing?

Thanks for any advice.
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Old 08-21-2011, 08:57 PM   #2
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Originally Posted by Skyrex View Post
I'm changing the pads and rotors on a 2000, A-6, 4.2L. The rear caliper piston won't retract when trying to run it back into the caliper housing with the disc brake piston tool. Same problem on both sides. The piston just seems to spin when I push and ratchet it inward. Sometimes it feels like the piston is binding up as it turns, rest of the time it turns freely. The piston appears to have right hand threats. I tried opening the bleeder valve to release pressure. Also tried to retract the piston using a C-clamp. The piston was well extended as the pad was worn down to approx. 1/8".

What am I missing?

Thanks for any advice.
Try to use a c-clamp or similar to push it in and adjustable pliers or similar tool to turn it. As it goes in a bit, tighten the c-clamp a bit further to push. That should work. Make sure parking brake is not engaged. It may be that it is too far out and a spring etc. is not letting it catch the grooves...
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Old 08-22-2011, 08:51 AM   #3
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You mention using the disc brake caliper tool - so I'm not sure if you have the correct tool or not. There is a kit you can rent from Autozone that has the correct parts - the tool is like a standard caliper tool that presses against one side of the caliper while the screw pushes the piston into the caliper. However, the tool has plates that fit in the slots on the piston and "screw" the piston in while pressure is being applied to force the piston inward. If you have this tool, then this is correct. If not, rent it from Autozone for $35 and keep it, or return it and get your $35 back.

If you are using a c-clamp or the standard tool that just presses inward, you can damage the piston like this.

If you are using the right tool and it is binding still, the caliper may need rebuild or replacement. Replacement is probably $80 and not a hard job if you have it off already...
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Old 08-22-2011, 09:14 AM   #4
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^ Correct, the rear pistons actually screw in to retract and you therefore need the correct dedicated caliper tool. A 'C' clamp is fine for the front pistons, but not the rear.


Make sure the caliper tool is 'locking into' the piston face so that the piston is actually being engaged and you're not just spinning the tool itself freely.

btw: my 2011 requires rear caliper piston electro-mechanical retraction (VCDS tool or the like). At least you can still do yours the "old school" way.
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Old 08-22-2011, 08:48 PM   #5
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^ Correct, the rear pistons actually screw in to retract and you therefore need the correct dedicated caliper tool. A 'C' clamp is fine for the front pistons, but not the rear.


Make sure the caliper tool is 'locking into' the piston face so that the piston is actually being engaged and you're not just spinning the tool itself freely.

btw: my 2011 requires rear caliper piston electro-mechanical retraction (VCDS tool or the like). At least you can still do yours the "old school" way.
Agree with getting the right tool. I was able to get away with just a c-clamp and adjustable pliers (not the locking ones) and turn them. It's a slow process but worked anyway.

Also, on my bro's '07 passat, they have to be done via VAG-COM as they have motor in them. Easy but, if that motor goes, whole caliper is in jeopardy...
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Old 08-22-2011, 11:47 PM   #6
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Everyone - Thanks for your suggestions. As soon as I got the caliper in the bench vice and standing up, I was able to thread the piston back into the caliper. I was using one of the cube piston tools with ratchet and extension. Didn't do anything different and the piston turned the same as it did before. This time it did retract. It may have been my tool and trying to retract the piston in a horizontal position. No other problems found inside and I had the same problem with both calipers.

Thanks for the support.
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Old 08-23-2011, 03:54 PM   #7
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One thing is to free up the dust boot around the piston with a pick before you start turning the piston. I destroyed a dust boot once because I didn't do this and the dust boot rotated with the piston and tore. Replacing the boot is a PITA because you have to blow out the piston (might as well replace the seal in the cylinder..it comes with the kit!), put the boot on the piston and turn the boot inside out and install the piston in the cylinder part way...turn the boot right side out and press it onto the cylinder and finish retracting the piston.
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Old 08-23-2011, 03:54 PM
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05, 2000, a4, a6, a8, audi, brake, caliper, piston, rear, retrack, retract, retracting, software, vcds


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