My dad has a 1995 ranger that had a brand new brake booster put on today. My dad is a very experienced mechanic but can't pinpoint exactly what is causing the pedal to go to the floor. he has only replaced the brake booster. he has not bled the lines. There was a leak on the rear right tire and he checked to see if the gasket was broken and it is not. He knew it'd been leaking for some time but he said its not now. He said the master cylinder is good and hasn't been taken off at all. I'm not providing all the information involved but I will continue to add as he comes home. Any suggestions would be helpful. Thank you!

 

Welcome to the forum

Brake pedal going to the floor has nothing to do with power booster, hard to press brake pedal is power booster issue, brakes still work fine just hard to press pedal down

When you press down on a brake pedal it pushes Master cylinder's piston to the front, in a 1995, this will cause brake fluid to be forced out of the TWO brake lines attached to master cylinder, front brake line is for REAR brakes, back brake line goes to FRONT brakes.

If there is a leak in any hose/line or slave(the part at the wheel) then pedal will go down to the floor as fluid flows out of the leak

System depends on fluid in master reservoir being full
And that the masters piston seals are OK

Air in the system will cause a "mushy pedal" and you may be able to push it to the floor but there would be some resistance
No resistance is either a big leak or a bad Master

1995 has rear brake shoes so wheel cylinders as slaves, if rear brakes are out of adjustment then these cylinders can expand too far and pedal can go down very low, but not to the floor without a leak on that wheel