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Discussion Starter · #1 ·
So I pulled the brake calipers off my rotor and took out the brake pads. After I pushed the pistons all the way back and since I was curious how it worked i then pull the brake lever a bunch pushes the piston back out. Now the piston is too far out and I cant get brake pads in and I cant get the piston to go back in. I have tried pushing with the bleeder valve open as I thought it was a pressure problem. Anyone know why it would go in originally and now wont?
 

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Discussion Starter · #3 ·
How far in does it go? Wondering if it wasn’t pushed straight back in
so the first one with the new brake pads in is the front left and the one without the brake pads in is the front right. I cant get the front right callipers in enough to even put the brake pads in. Do I have to open both valves or how do I make it so there is no pressure so i can easily push them back?
 

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You have a couple of additional opportunities, pushing the rusted piston back in may rip the o-ring in the caliper creating leaks. The amount of rust on the pin where the pads slide has a tremendous amount of rust, remove the pin, sand it down to remove the rust and then some grease to prevent rust in the future. Back to the pistons, I would remove them and replace or at minimum sand them down with fine sandpaper to remove rust & crud. Likely the ones that are refusing to go back in are slightly cocked in the bore, again I would remove all the pistons and clean up while it's apart. That would also allow you to clean the crud out of the caliper, brake fluid absorbs moisture and performance deteriorates. I'm betting there is a lot of black crud behind the pistons. If you refuse to correct the problems just stick a screwdriver between the pads and pry them apart, what's the worst that can happen.
 

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Discussion Starter · #5 ·
You have a couple of additional opportunities, pushing the rusted piston back in may rip the o-ring in the caliper creating leaks. The amount of rust on the pin where the pads slide has a tremendous amount of rust, remove the pin, sand it down to remove the rust and then some grease to prevent rust in the future. Back to the pistons, I would remove them and replace or at minimum sand them down with fine sandpaper to remove rust & crud. Likely the ones that are refusing to go back in are slightly cocked in the bore, again I would remove all the pistons and clean up while it's apart. That would also allow you to clean the crud out of the caliper, brake fluid absorbs moisture and performance deteriorates. I'm betting there is a lot of black crud behind the pistons. If you refuse to correct the problems just stick a screwdriver between the pads and pry them apart, what's the worst that can happen.
So the one that had brake pads on I was able to get the pistons back in place by just using pliers. I cleaned up the calliper then through it back on the bike. The problem Im having trouble with is in the second picture. The pistons just wont go back in no matter how much force I put on them.
 

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Use a bigger prybar - that is not a serious suggestion. If you insist on just slapping it together move the pads out of the way, the piston is cocked in the caliper bore. You have a lot of bad stuff going on that really needs to be addressed, goes back easy when you fix all the problems. If the pistons don't go back in easily do you think they will extend as designed when you pull the brake lever?
 

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Discussion Starter · #7 · (Edited)
Use a bigger prybar - that is not a serious suggestion. If you insist on just slapping it together move the pads out of the way, the piston is cocked in the caliper bore. You have a lot of bad stuff going on that really needs to be addressed, goes back easy when you fix all the problems. If the pistons don't go back in easily do you think they will extend as designed when you pull the brake lever?
Who said I insisted on just slapping it together. I cleaned the other one after I got the pistons moving and am going to do the same to this. Was able to pull them out and they are clean and no black gunk in the bores like you said there probably is. The left piston goes in but the right one keeps giving me trouble. I wiped down the pistons and its completely clean. The inside of the bore is completely clean too and it still doesnt go in. I am asking if its a pressure thing or the right technique to get it back in cause it is not stuck as it was working before I pulled on the brake lever.
 

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Assume you're putting it back together as since you have the pads mounted and looks like you were ready to install the caliper. How are you cleaning the rust off the pistons? Pull the pistons out clean them (gunk & rust) lubricate with brake fluid and reinstall

The piston is cocked in the caliper bore (for the 3rd time), it won't be visible when you're looking at it or there's something behind the piston preventing it from retracting. You said there wasn't anything behind the pistons in the other caliper so I will stick with the piston is cocked in the caliper bore. After 40 years of working on 100's of motorcycles I can assure you I am not confused.

The piston to cylinder clearance is very tight, just a bit off and the piston won't retract
 

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Discussion Starter · #9 ·
Assume you're putting it back together as since you have the pads mounted and looks like you were ready to install the caliper. How are you cleaning the rust off the pistons? Pull the pistons out clean them (gunk & rust) lubricate with brake fluid and reinstall

The piston is cocked in the caliper bore (for the 3rd time), it won't be visible when you're looking at it or there's something behind the piston preventing it from retracting. You said there wasn't anything behind the pistons in the other caliper so I will stick with the piston is cocked in the caliper bore. After 40 years of working on 100's of motorcycles I can assure you I am not confused.

The piston to cylinder clearance is very tight, just a bit off and the piston won't retract
Yea that was the other side. There are two photos on that Imgur upload I know its hard to see but if you hover over the image and click on the arrow you can see the other brake. The one that is giving me troubles is not rusted up like the other one. I have pulled it out and cleaned it with a microfiber towel and brake fluid and took all the brake fluid out of the bore and cleaned it but when I try to push it back in it does not go. On the front right caliper the top piston goes in and out but the bottom one wont no matter how much I clean it. I am not sure why its being cocked. I did not mean it like that I am sure you definitely know what you are doing I am just talking about why the piston wont go in even tho its clean. No bad blood just a misunderstanding.
 

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Remove the piston, use a very fine sandpaper (1,000 may 800 grit), sand the piston, if you're leaving deep scratches, stop and get finer sandpaper. Scotchbright pad works too,, once it's smooth coat with brake fluid, and it should slide in. All the grunge and rust has to be cleaned off. If there's any build-up on the bore of the caliper it will need to be cleaned/smoothed before the piston will go back in and move freely. Open up the bleeder valve, since the brake fluid is out only air should come out.
 

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Discussion Starter · #11 ·
Remove the piston, use a very fine sandpaper (1,000 may 800 grit), sand the piston, if you're leaving deep scratches, stop and get finer sandpaper. Scotchbright pad works too,, once it's smooth coat with brake fluid, and it should slide in. All the grunge and rust has to be cleaned off. If there's any build-up on the bore of the caliper it will need to be cleaned/smoothed before the piston will go back in and move freely. Open up the bleeder valve, since the brake fluid is out only air should come out.
Yea I am cleaning the right front calliper right now. Been busy the last couple days but have finally been able to continue this project. Im seeing that the dust rings are shot on it so ordering some new ones now. Thanks for all the help and advice Ill let you know how it turns out.
 
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