Caliper piston removal with caliper off bike?

[ironsheik]

Hey all,
I just repainted my master cylinder and calipers in preparation for a front brake rebuild with stainless lines and I ignorantly removed the calipers without pushing out the pistons. So I know I can do this with a compressor but I don't know how. I can borrow a compressor but can someone tell me the specifics? I don't want to blow this thing apart in my hands! I suppose I use the bleeder valve to blow into and plug up the brake line connection? Thanks for any help. I can't wait to get my bike back on the road!

Josh

[80GS750]

sounds like you got it figured out....

just block the brake line, and put some pressure into it..

make sure nothing is in the way though, cause it will pop out of there with some force...

[Dogma]

Hey all,
I just repainted my master cylinder and calipers in preparation for a front brake rebuild with stainless lines and I ignorantly removed the calipers without pushing out the pistons. So I know I can do this with a compressor but I don't know how. I can borrow a compressor but can someone tell me the specifics? I don't want to blow this thing apart in my hands! I suppose I use the bleeder valve to blow into and plug up the brake line connection? Thanks for any help. I can't wait to get my bike back on the road!

Josh

Whichever way you can cobble it together without damaging the caliper will work. Just keep your fingers out of the caliper while doing it.

In my case, I cut one of the old rubber lines so that there was a banjo on just the end attached to the caliper. Then I set up my little emergency compressor with the attachment for inflating rafts, air mattresses, etc. I shoved this little cone-shaped thing into the open end of the brake line and turned on the little compressor. Pressure built to maybe 30 psi (I think. It happens quickly). The piston poped out with a clang against the other side of caliper. The first one I was holding in my hand. The second one I held on the ground with my foot. Since then I read a story of someone who had the piston jam in the bore when it smashed his finger on the other side. Since the piston was jammed, it had to be forced back into the caliper before he could get his finger out. Treat it like a saw or any other power tool: Always be aware of where your parts are, and where it's parts might go.

[BrianMcDonald]

Had the same problem just last week...

A buddy of mine and I just had this same issue. Both of us are just starting out on bike maintenance - what can I say...

We left the bleeder valve in and used a rubber attachment (found it at Lowes in the air compressor aisle for like $3) on the air compressor to snug into the brake line bolt hole. We were able to pop out one of the front caliper pistons on his Goldwing at about 80psi or so. The piston came out really, really hard. His bike caliper wraps around so we put a block of wood on the far side covered in rubber to give the piston something nice and relatively soft to hit. Still - my ears were ringing for a few seconds after the pop.

The second one wouldn't budge even with that much pressure. We ended up rigging a way to lever it out by the lip where the dust boot slips in. Seemed like it was out of the way enough where it wouldn't compromise the piston seal, but it's not a smart way to do it, that's for sure. I have the banged knuckle to prove it.

For the rear, we used a similar technique - you can't realistically use air pressure if the caliper is a dual piston system because one of the pistons is fed by a fluid channel inside the caliper body and there's no way to seal that hole well enough.

I did have a question about the right way of doing this. If you use the brake system to pop the pistons out how do you manage the flow of pressurized oil when the piston comes loose? Or do you just run it close to the edge and pull it the rest of the way out by hand?

[80GS750]

i would get it close and then take it out by hand if its possible.....