Brake Booster blew off with bracket still attached

You probably had some metal fatigue at the welds, how old is the trk/trl i would clean up the other mounting location and look for cracks around the brackets on the other brake chambers. If any are questionable grind old welds and reweld

 

Sounds like fatigue more than anything to me. I have welded many it is best to remove it from the truck. If your not an accomplished welder hire it out or buy a new one. it will be an oem item all makes are made differently.
Stroke to long or short had nothing to do with it.
120 psi at the gauge doesn't mean 120 at the chamber. If the truck doesn't have an application gauge , you would need to plumb one up to check that. under normal braking 20 psi is a good bit, 30 on most trucks will put you in the wind shield.

 

Rough roads and vibration caused it to break off. Like the others said. Brace it and weld it good. Don't shorten or lengthen your stroke at all. You need a 90 degree angle with brakes released for best braking. Unless someone that didn't know what they were doing when replacing chambers got their hands on it they should all be at 90 degree angles

 

stroke wont casue it to break. its the force. on a standard stroke chamber the stroke has most force around 1 inch and gradually reduces as it goes down. is your truck set up for anti-compounding? if not then that could be the casue of the break or if the bracket is not gussetted. wide based tires? vibrations from the larger tires have been an issue in breaking the welds also.