2000 model rear brakes suddenly hardly work

Hi guys and girls, I haven't posted hear before because I've never needed to.  The issue is the rear brake. All I've done is take the wheel off to change the rear tyre and now the rear brake hardly works. I changed the fliud and I've got a firm pedal and made sure the pads aren't glazed and it's still crap.  Now I've run out of ideas and need  suggestions or advice. 
Thanks.

Two possibilities -  If your piston was grubby when the pads/piston were retracted to allow the disc back in, the piston can bind.

Check the brake pad locating tabs are seated correctly in their detents, they can be tricky little buggers to get in.

I've had it apart twice now and I was thinking the same thing so I've already checked to make sure they're free.  I even sprayed a tiny bit if lube  around the piston to make sure it's not sticking. They seem to be mmoving in and out OK.

A few questions come to mind. 
Did you need to force the pads out to put the wheel back in?
How worn were the pads?
Did you bleed the system when you changed the fluid?
Has the setting on the brake lever changed?
What happens if you change the setting on the lever?
Is this an ABS system?

A non-ABS hydraulic brake is a simple system and should be able to be easily sorted.  If it's not binding as tag has established, a full bleed might be in order.  Rear pads are cheap as chips and if they are getting down, chuck them and put some new ones in.

The pads pushed back no harder than normal when I put the wheel back on and the pads are about 90%. I've bled it and it's nice and firm it feels like the pads are made out of wood.  I'm starting to think I have a master cylinder problem not pushing enough pressure to the rear.

It's mot ABS and the pedal is the same

I'd be tempted to re-do the bleed.  How many k's has she done? I only ask because I haven't heard of a Bandit rear master cylinder needing an overhaul.

I'm bleeding it right now.  I even cracked open the master cylinder line and got no air. I'll test ride it in a few minutes and get back.

Still crap.  At least I know there is no air in the system now.

It's got to be the caliper because when I bleed it,it pumps the fluid out no problems out of the bleeder

It may sound silly ,but if your pads & disc have wear grooves in them , & now they don't quite line up after being disturbed with the tire change , it may just need a good workout through your favourite twisty road to get them nice & hot & re-bed the pads to the disc...............the Bandit rear brake is a bit wooden with the orig. pads anyway .............assuming the re-bleed doesn't work that is  .

Hmm, a new problem that hasn't come up before or just something we're not getting?  You're probably asking yourself the same question! 

So, the only things that have actually changed are (a) the manual pushing back of the pads and (b) new fluid and system bled.

Hard to see why either would lead to the problem you're experiencing.  It was brand new fluid wan't it?

PS: You forgot to mention the k's.

Is there braking at all?
Pull them out and sand the pads and wet n dry the disk.

Oh by the way we didn't need to reply either.
I hope you've introduced yourself in the appropriate forum now that you've "needed us".

I introduced myself about a year ago.  
I just took the caliper off again and checked the pistons are moving freely and it all seems fine. They move in and out ok. The bike only has 60000ks on it but it is  almost a 15 year old bike now.  It has brand new fluid.  I'll go and test ride it now.  If it doesn't work right I'll go and get new pads tomorrow and try them.

Cool mate. My apologies in that case.
But don't be a stranger

Well thanks everybody for your help and opinions.  I think by forcing the pistons fully in and pumping then back out a few times I may have dislodged a bit of grit or something which may have been jamming one of them.  Took it for a burn and they work now.  I hate it when you fix something and don't really know how or why it works again without a positive solution.  The main thing is that the rear brake works again, I just hope it stays that way.  

Again thank you everyone
Carl

Ride safe mate. Catch ya soon - Parkes?

Good news ..glad you got it sorted