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Discussion Starter #1 (Edited)
Yesterday I started on the brake re-build for my RD03. This bike had been sitting for a few years with the brake systems drained and partially disassembled.


Problem: How to remove the old crusty brake pistons from the caliper while not destroying them in case they can be cleaned up and reused.


One solution was to re-assemble the entire system, bleed it and use hydraulic pressure to push out the pistons.


I thought I might be able to get it done without all that messing about with brake fluid (and the fact that both master cylinders also need a rebuild and would likely not pump any fluid anyway).


Here are the steps. Log this in your shade-tree-mechanics file.


First you repurpose two parts of the old brake system and murder one piece of it. I have to stop here and say that the lines are being replaced with braided flex lines so the old lines will be binned anyway.

IMG_2349.jpg


Here's what you need. The OEM fitting that holds the metal flared brake line into the flex line is removed. It is then drilled out to 6MM.


Next you have to murder a bicycle PRESTA inner tube. If you're a cyclist, you'll likely have a few punctured tubes on a hook somewhere waiting for a rainy day when you can patch them all. If you're not a cyclist, any good bike shop will have junk tubes lying about or in the trash. Ask nicely for a PRESTA tube. Should be a freebie.


The standard SCHRADER valve stems don't work because they are about 7.6 mm and too large to work in this application since no rubber is left to seal it into the old brake line.


Have a look at the PRESTA stem at the right of the photo above. The stem is cut off the inner tube and then sanded down so it fits tightly in the flex brake fitting at the top of the photo.

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Then the fitting that was drilled out in the first step is screwed down onto the rubber PRESTA stem making a pretty good (but not perfect) seal.
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Next connect the flex line to the brake caliper. I found that inserting about 5cc of brake fluid into the line helps to seal the PRESTA stem and also probably helps to lubricate the crusty old brake pistons.
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Next, insert some piece of metal between the pistons and the brake caliper. As you start to pressurize the system you've created one piston will likely start to move before the other. What you do NOT want to happen is for one piston to come completely out of the caliper and the other to still be stuck inside with no way of pressurizing the system again. NOTE: since you are using a PRESTA valve stem, you must also use a PRESTA pump or at least a pump that can accommodate both PRESTA and SCHRADER. Standard SCHRADER pump fittings will not work with PRESTA valves.
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So one piston will begin to extend until it hits the stop you've built. As you can see, you can put in a fairly thin piece of stock (or an old wrench) and still not have the piston come all the way out of the bore.


I was able to create about 140 psi with my bicycle pump before the pistons began to move. I had to take several strokes with the pump and hold the pressure for about 5 minutes as the old pistons finally conceded to move out of the bores.

And - no - the vise grip marks (arrgghh) on the pistons are from a previous owner....not mine !!


As the pistons move almost to the stop you have in place, you can reduce the pressure on the pump. The last 5 mm or so of movement was done with only about 40 psi necessary to make the piston move.



Once they pistons are out this far, you can remove the stop and just pop one out of the caliper, The other it far enough out to be removed with your hands.


...............Sucess...............
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The advantage to this method is using stuff I already had in the shop. And the bicycle pump is a bit of a safety factor since the pressure can be reduced as the pistons reach the end of their travel. At the end one will just make a soft "pop" when it comes out.


Hopefully this will help someone
 

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Very interesting article, indeed.
Usually when I want to remove pistons, I remove brake caliper from bike, then I press brake lever to push pistons out. You made a good point of not letting one piston get out before the other is nearly popping out too.
 

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i just sprayed loads of WD40 in there and pulled them out with a pair of pliers, using a piece of rag in-between the pliers so not to damage the pistons
 

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For really stubborn ones you can replace the bleed nipple with a grease nipple block off the banjo bolt hole and pump them out with a grease gun.
your way is much safer than the way i took them out of my xr400 a few months ago. Apparently using a compressor and your fingers to control the pistons on the way out is not a good idea lol














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