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Discussion Starter #1
My 2007 had a front brake dragging. Got red hot. I had to drive the caliper off of the rotor.
I wanted to put a piston kit in the caliper, but I can't get the piston all the way out.
I push it in and out about an inch, about 3 different times but I can't get it to pop all the way out.
Any tips?
 

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If the caliper is off of the rotor but still connected to the brake lines, you can remove the pads and pump the brakes. It should pop out if there is no air in the system. If it got hot enough to boil the fluid you could have air in the caliper cylinder. If it is disconnected from the brake lines, try what showtime recommended. If that doesn't work, reconnect the caliper to the brake line, make sure the brake fluid reservoir is full and bleed the caliper to be sure there is no air in the caliper cylinder. Wrap a shop towel around the caliper and pump the brakes. There should be more than enough hydraulic pressure to pop that piston out. The towel is just to keep things from getting too messy.
 

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The piston or bore could be damaged enough that it won't come out, which would require a new caliper. I hope it doesn't come to that, but OEM calipers are relatively cheap and someone on the Sky forum has some leftovers: Free front brake rotors

Using brake pressure to pop the piston out will work, but will also make a mess. I would not use air. The energy released when the piston blows out can make it a pretty dangerous projectile.
 

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I would not use air. The energy released when the piston blows out can make it a pretty dangerous projectile.
Indeed - I have seen them fire all the way across a shop and make a significant dent in whatever stops them. We used to use an adaptor that screwed into the bleed nipple hole and attached to a grease gun. Point the caliper into a garbage can and pump. Doesn't seem to come out with the same velocity as air pressure makes it and in any case the can catches it.

Another way that usually works is to simply slam it down by hand (with the frozen piston directed downward of course) on a hefty chunk of wood. That often shocks it out but shouldn't be risked if a particular caliper doesn't look chunky enough to take it.
 

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Air is dangerous because it compresses. As you build up pressure behind the piston you are pushing a large volume of atmospheric pressure air into the cylinder. When the piston pops out that large quantity of air returns to its un-compressed volume, and that expansion is what creates the danger. Oil, brake fluid, and grease are not compressible, so they have the same volume at any pressure. This means that there is no expansion when the piston pops out and it therefore exhibits minimal ballistic behavior.
 

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Air is dangerous because it compresses. As you build up pressure behind the piston you are pushing a large volume of atmospheric pressure air into the cylinder. When the piston pops out that large quantity of air returns to its un-compressed volume, and that expansion is what creates the danger. Oil, brake fluid, and grease are not compressible, so they have the same volume at any pressure. This means that there is no expansion when the piston pops out and it therefore exhibits minimal ballistic behavior.
I always put a hammer handle across the caliper opening. Softens the blow when the piston hits it and doesn't damage the piston. Never had one fly anywhere in over 40 years of rebuilding calipers and it's not messy. I guess if you're not comforatble with it don't do it. Never had one not come out.
 

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Discussion Starter #9
Stupid mistake. I took the whole caliper out and took it to work to see if my buddy could help me. We decided I should put it back on and start the car when I press it out with the brake pressure. Worked fine. I probably did the same thing on a car about 44 years ago... finally learned something. Thank you all for the words of wisdom.
 

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And what exactly is unsafe about doing that way? I gues if you're stupid and use full shop air you may be stupid. Did you do it that way John?
As for what is unsafe about using air to eject a stuck piston, read my earlier post. You may understand it, or not. You may believe it, or not. You may care about my opinion, or not. Either is fine because I am not responsible for your actions or your safety. We all make our own choices and then live (or don't) with the results. That said, if someone whose knowledge and abilities I have no way of judging asks for advice about how to do something, I am not going to suggest a method that requires additional cautions if there is a safer alternative. And I certainly would not do it without making it very clear what the risks are.

No, I have not done it that way. What I have done is spent the last 40 years in a variety of industrial settings where I have had to clean up the messes left by some idiots who have done similar things with unpleasant results. Filling out the paperwork for the accident report is almost as much fun as cleaning up the blood.

In most of the injury accident reconstructions we have done the injury was caused by the intended result happening either sooner or more abruptly than the injured person (a bystander in some cases) expected or planned for. And the comment that is almost always made? "I've been doing it that way for years, and never had a problem, I don't know what could have gone wrong."
 

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Discussion Starter #13
Thank for your help and words of wisdom. Everything went well after getting the piston out.

There were rust flakes packed around the piston ring. It didn't come from the piston though, and it all cleaned up well. New rubber parts and silicone grease to make sure the boots sealed well and lube the slides. I didn't know how to check the old rotor so I just replaced it.

It looked like the last person in there just slapped some shoes in and then went on to cross threading all of the lug nuts. It looked like the old pads had never touched the rotor until they finally moved once and locked up. All of the lug nuts but one have been damaged by cross threading them.

Now I know I need to do all the rest and buy a whole set of lug nuts.

I really enjoyed doing it, and it's great to have you guys around to share problems and solutions!
 
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