Could it be that since he changed fluid, without taking the cap off he won't be able to pry them open fully? Too much fluid in the system possibly? Dunno...

 

If he changed the fluid, pumped the pads together, then filled the master cylinder back up it definitely has too much fluid in the system. If the pads can not be easily pried apart it is because the pads are hydraulically locking in place. The fluid behind the pistons has to have some place to go when the pads are pried apart and there may not be enough room.

Pull off the MC cap, suck out about half the fluid, put on the cap, but not tightly. Now pry apart the pads with a screwdriver or the like. You will see somehow the master cylinder is nearly full again - it's magic! Do this then refill the master cylinder a bit if needed.

You won't get any air in the lines unless you either suck all the fluid out before doing what I said or if you lay the bike on its side while doing what I said. Neither of which make any sense or should be done.

PS:
They are right, it is possible to cause a little geiser to erupt from the return hole if you leave the lid off the master cylinder while forcing the pads back. Thus the reason why I say put it back on loosely. It's like putting a Dixie cup over a male baby's "shooter" while changing diapers. Stop the squirt before it gets you!

 

No, it won't squirt fluid anywhere. It will just rise slowly. He's not going to be able to push the piston fast enough to cause squirting.

The main thing is to watch the level. If he filled it up with the piston out, then the level will be high and may overflow when he pushes it in.

As far as debris getting in with the lid off, I don't do this type of maintenance in a windy, dusty area.

 

Taking the cap off the reservoir on the handlebar will not add air to the system or let debris into the reservoir unless you're a clutz and/or didn't clean the area around the cap of dirt/debris before removal.

As others have stated, since the OP probably filled the master cylinder reservoir to the full level after servicing, when he pushes the pads in at the caliper, the pistons will indeed push more fluid into the reservoir...not really good...and the pads will possibly creep back out because of too much fluid. Then you can have drag...not good. Yes, you can definitely get a geyser of brake fluid if you spread the pads at the caliper with any quickness. Slowly spreading the pads will not cause this...just go slow. I'll bet some fluid will have to be removed from the master cylinder reservoir with a syringe or such to get the level to normal full.

Now, there is another way to pursue this. Get a clear piece of tubing that fits the caliper bleed valve snugly and attach it to the valve nipple. With the disc rotor out of the caliper, get your big screwdriver or whatever you'll use to spread the pads/pistons. Now as you start to spread the pads with your tool, crack open the caliper bleed valve about a 1/4 turn and allow the excess fluid to flow out the valve, through the clear tube, and into a catch container. When you've spread the pads to their max opening, close the bleed valve. The fluid in the bleed valve and clear tube will keep air from going back into the caliper if you've made sure the tube points up from the caliper before making its downward angle to the catch container. The reason this is a better way to bleed excess fluid is that this method actually balances/equalizes the brake fluid pressure in the system with the pads at their fully expanded position which will assure no pad drag during operation. Pads worn down nearly to their limits may require adjustment of the lever so that freeplay is not excessive, but that's about the only issue with this method. Many bikes that have dragging pads and rotors can be addressed with this method as long as the cause isn't from other issues like a seized/sticky piston, master cylinder malfunction, or other service issue that needs repair.

 

Don't forget, brake fluid is nasty stuff. It will eat paint quickly. Be very sure to prevent that stuff from squirting all over.

Want to vandalize a car? Dump brake fluid on the hood.

 

I hope your calipers aren't dirty. Letting the pistons come out all the way like that is very bad. When you push them back in and have dirt around the o rings you stand a very good chance of messing up the o ring and causing a leak at the calipers. This is to include the brake dust build up on the calipers.

 

i was able to push the pads apart fairly easy to their normal position. I didnt check the reservoir but i will..