calipers locked up

So i had a little fender bender this morning(rear ended a semi trailer at very low speed) after the impact my front calipers are locked up?? i found if i remove the vacuum hose from the master cylinder it "hisses" and relieves the pressure and the calipers are free until i start the truck again and hit the brakes, then they lock up again.....anybody have any ideas??
its a 06 double quad cab prerunner with the V6

 

Hmm. There's a diaphragm in there, perhaps it's leaking/torn/damaged somehow.

 

I think something maybe bent? my foot was on the brake pedal when the impact happened, the tow truck driver seems to think the rod from the pedal to the master cylinder is bent?? Im going to check it out today

 

Perhaps, if that were the case I would think it would be easily noticed, and I'm not sure if it would explain why the brakes release when you release the vacuum.

They'll figure it out with the rest of the repairs I'm sure.

 

Ok so truck has been in the dealership for 3 days now and there baffled...... there saying the calipers, rotors and pads need to be replaced......im not agreeing with this!
anybody have any ideas?
its covered under the insurance claim so its no money out of pocket(except my deductible) but I still don't understand how its possible for the calipers to lock up then up and unlock when the vacuum is released? I don't think its the calipers???

 

Take it somewhere else they are clueless.

 

Any updates? I'm curious to see what the problem is or was.