A forum for owners of Yamaha TTR250 trail and enduro bikes!

Assuming your brake master cylinder piston is  working properly and not jamming in the "on" position then you need to look at the condition of the pistons and seals in the caliper.

There are two pistons (part #4) and each one has both an oil seal and a dust seal. (part #5) 

If the pistons and dust seals are clean and free from dirt and corrosion then they have a certain amount of "flex" in that they will automatically pull back from the brake disc (rotor) when the brake lever is released.

With the caliper off (I think you have done this already) put a piece of wood (or a spacer of some kind) that will allow you to pump the pistons out about 10mm and check their condition. Spray some WD40 liberally around both pistons and clean the visible part of the dust seal (maybe use a toothbrush?) . Do they look intact and in good condition?

If not, replace both the dust and oil seals. If they look OK then try pushing the pistons in and out to make sure they are moving freely. If they now are, replace the caliper and check if the wheel now moves freely. If they aren't you will need to pop them both out to check and clean them properly and maybe replace the seals if they look worn or perished.

Sorry no photos. Can't believe I have never made a tutorial for replacing the seals 

Brian

I pumped out the pistons and washed and cleaned well. It was dirty. I have repeated it several times and it is good. WELL !!!
And the spring was stuck in the middle of ha ha.