Brake piston removal

The stirrup pump is rated to 120+ PSI but I was only pumping about 60 PSI as anymore pressure would blow off the pump connector.

Its sounds like yours are seized in abit, you might have to apply penetraiting fluid (WD40).

NB: Remember to un screw the brake fluid chamber lid to un pressurise the system !

What I'd do in your case is keep the brake unit on the bike - hooked up to the hydraulics but unbolted from the disc. If you can remove the pads this will gives you an inch of free space between the cups to work with.
The aim is to try to get the cups to extend out far enought so that you can get at them with a bit of emery paper / wd40.
I've got 2 retangles plates of metal with a drilled hole at either end and 2 nuts & long bolts connecting the plates either side of a cup. You extended the cup by pressing on the lever and then wind the the plates in by tightening the nuts & bolts. Keep repeating this untill cups extend and retract smoothly.

On the rear pad once you've cracked open the caliper into its 2 halves, you can punch/ tap out one of the shells through the unbolted bleed screw hole.

The other shell isnt so easy as the bleed bolt is not in the same position, this is where the bicycle pump came in. However there is a brake fluid flow hole between the two sides that needs to be blocked off. Cleverly you bolt the 2 halves of the caliper back together but with one of the sides reversed using only one bolt. This blanks of the flow hole allowing you to start pumping through the open bleed screw hole.

Originally Posted by Sid Squid

Easiest way if they're at all sticky, alternatively use an expander bolt to allow you to get a hold, and then pull/wiggle.

where about would I find a expander bolt that fits inside a piston? I googled a few but no idea if they are suitable looks like this



then something thats called a expander bolt too


many thanks for your helps!

Lucas

[yorkie_chris]

Originally Posted by no_akira

Its sounds like yours are seized in abit, you might have to apply penetraiting fluid (WD40).

NB: Remember to un screw the brake fluid chamber lid to un pressurise the system !

WD40 isn't a penetrating oil, and in this case using plusgas, 3in1, duck oil etc would not be advisable if you were intending to reuse the seals.

The compressor side of things i agree with YC a bit of rag, i used a thin bit of wood when i did mine then just pulled the pistons out as they were that far out, also depends on how much you pull the trigger, pull it gently they should just slide out, pull the trigger right back and then its time to take cover

[yorkie_chris]

Pressure =/= flow

pistons are very stuck

I'll be linking them back up to system to pump out, just how far, in terms of mm, will the pistons go before popping out?

also, does tying back the brake level actually close the system? hence stopping the fluid from master cylinder draining out?

cheers,

Lucas

How much of the pistons are protruding? Try to get some molegrips covered in rags on them. Don't try to pull them out, rotate them first, then gently pull upwards while twisting.

[Dave20046]

Originally Posted by Lucas

pistons are very stuck

I'll be linking them back up to system to pump out, just how far, in terms of mm, will the pistons go before popping out?

also, does tying back the brake level actually close the system? hence stopping the fluid from master cylinder draining out?

cheers,

Lucas

Not sure in terms of millimeters (possibly 30 or 40?) but basically the full length of the piston and they don't pop out when pumping they pretty much just fall. Just strip your calipers so it's just the pistons in there (no pads or securing plate at the bottom etc.) , wedge a spanner or something across both pistons on one caliper and pump the other caliper, they'll start coming out - use your thumb or spanner or something to slow one piston if it's coming out faster than the other, you want them coming out at the same rate. When they're almost there wedge something down that caliper and do the same process on the other caliper. Then just edge them out a little at a time, if they're all at the same rate as soon as one drops out it'll be easy to just pull out the others with your hands.

[Dave20046]

Originally Posted by Lucas

also, does tying back the brake level actually close the system? hence stopping the fluid from master cylinder draining out?

oh and unless you have a leak in your system no the fluid won't drain.

[yorkie_chris]

Yes the MC will drain with the lines disconnected.