Stuck break calipers. Help!

[LCK]

Weaker than usual front breaks on Lexmoto Arizona, (double cylinder, + yes I know its a Chinese bike...)
I have a fair bit of mechanical confidence, so decided to remove caliper, clean pads, etc. after watching a few videos. Cylinders were well cruddy and rusty, so i gave them a scrub, pumped break gently to check movement.

One cylinder moved out a bit, the other a fair way out, but not popped out (whew..). But,.. neither of them will move or twist or anything. Tried gentle persuasion with plumbing wrench.

Am I right in thinking the next stage involves a big C clamp to push them back in? I also used very fine grade sandpaper and WD40 on the pistons only (advised by MCN tutorial), they still have a little corrosion.)

1. Do I push one cylinder, until even with other one, before clamping both and pushing back together?(I know if you push one, the other moves out.

2. Will I need to bleed the brakes/ open the valve to do this? Some say yes, (HOW THE HELL DO YOU QUICKLY OPEN AND CLOSE THE BLEED VALVE WHILE CLAMPING?) some say no in other forums. Confused.

3. Is a clamp the best way to do this?

Thanks in advance for wise words, I realise it is dangerous to fiddle with breaks if inexperienced, but thorough testing will follow on a quiet road. Gotta learn how to service them someday!

[Rogerborg]

Take the top off your master cylinder reservoir or at least loosen it to allow air out.

The pistons should push back in by hand.

If they need more than that then it's likely that the seals are swollen or there's corrosion or dried up brake fluid in behind them.

If you're going to do it properly, the pistons and seals will have to come out and you'll need to clean behind the seals and possibly replace them. A slightly blunted dental pick is ideal for fishing them out and cleaning out the grooves - you can get them in some supermarkets.
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Biking is 1/20th as dangerous as horse riding.
GONE: HN125-8, LF-250B, GPz 305, GPZ 500S, Burgman 400 // RIDING: F650GS (800 twin), Royal Enfield Bullet Electra 500 AVL, Ninja 250R because racebike

[RhynoCZ]

What Roger says and NEVER use any inappropriate tools, such as pliers to push the pots in or pull them out. Damaging the pots is the last thing you'd want to do.

Loosen up every single bolt, that you're gonna need to be loose later, before you take the caliper of the bracket/fork. Then use the MC to push them all out. Do it equally, put something between the pots to do so.
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'87 Honda XBR 500, '96 Kawasaki ZX7R P1, '90 Honda CB-1, '88 Kawasaki GPz550, MZ 150 ETZ
'95 Mercedes-Benz w202 C200 CGI, '98 Mercedes-Benz w210 E200 Kompressor

[DRZ4Hunned]

Doing this job myself ATM, what a pain in the arse! Took the calliper off as I watched some guy on youtube do it but couldn't get mine out manually, so had to re-attach and re-bleed to try and pump them out hydraulically. Managed to get the brakes working but they'd only pump out partially, think the system may need bleeding again.
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DRZ400-SM
FZS600

[RhynoCZ]

[Pigeon]

Also, don't get WD40 near the rubber seals. They absorb it and expand massively, completely blocking the piston........not that I've done this

[Kwakki Si]

[kramdra]

[LCK]

Thanks for all the tips.
What worked= opened up main bleed valve, table to rest caliper on, screwdriver neck to press down pistons, topped up break fluid (in the nick of time!!)
Road test = great success, functioning brilliantly.

[Kwakki Si]

[LCK]