so i got 1982 toyota 2wd truck i just put new brakes on it front and rear put new master cylinder and they worked for a while than one day they were good tell i drove about 4 miles than i had no brakes so i bought a new booster thought that was the problem nope still doing the same thing i tryed bleed my brakes but nothing will come out of it. so give me some ideas what it could be. and now my truck will start up but once i turn the key off the motor will keep going.

 

Did you bench bleed the new master cylinder? It can take a while to get all the air out of the master cylinder and you could have some air left in there and not know it. Since it's in the truck you can do a gravity bleed, just make sure the resevoir stays full.

Now, with regard to the engine running after you take the key out....
Does it run normally when you take the key out? If so, I'd say maybe your ignition cylinder is bad. Does the key just kinda fall out and flop around in the cylinder or is it firmly in there?

Or does the engine run really rough when you take the key out? If it runs rough it sounds like your engine is probably 'dieseling'. I've had a truck do that because the head got warped and I basically ruined the engine.

 

yes i did bench bleed it than i tryed the gravity bleed and the black bleed but not the front i just dont see why i would lose brakes after everything warmed up. i found the problem out it not shuting of a wire cameing un done

 

are your rear brakes adjusted properly? Did you bleed the lspv? Bleed in the correct order ie : rear pass side, lspv, rear driver side, front pass side, front driver side?

 

Glad to hear you got the engine issue taken care of.

So if you're bleeding your brakes, but not getting anything out of the bleeders I'd say you've got a clog somewhere. And if you have a clog and you're not getting any brake fluid bled out of any of the corners you have to look to a central place......the master cylinder. try unhooking the lines from the master cylinder and rigging something up so you can do a gravity bleed thru the lines, but not have it going thru the master cylinder. If you're getting fluid out of the bleeders then you know your blockage is in the master cylinder.