Not a truck, but wanted a some quick input. Haven't looked at it myself yet, but my son's 98 mustang rear disc brakes are not releasing...
Dirt in the line? Something wrong with the master?

As always, thanks in advance.

 

This may not be your problem but I just looked at my daughter in laws 98 or 99 (I forget which) Mustang rear brakes and the pads had worn so thin that the calipers had extended all the way out and would not return. Talked to a buddy of mine and he said that thoses calipers would do that if the pads got to thin and you had to have a tool to actually screw ? the calipers back in. I have only fooled with the type where you just use the tool that squeezes the piston back in and then just replace the pads. You might want to check that first.

 

Lakotas,
A lot of rear disc brakes are that way (with the screw in pistons) so that they can have a parking brake mechanism.
They do parking brakes a couple of different ways with rear discs; one is to have the special calipers and pistons where the piston is manually "screwed" out when the parking brake is applied, the other common way is to have a special rotor that is both rotor and drum. The regular braking is with the rotor and cailper, the parking brake mechanism is a small diameter drum brake set up.

I have no idea what the late 90's Mustangs use
Good luck with it
Bobby

 

Could be a bad brake hose.

 

It might also be a rusted emergency brake cable.