So i just took over a title for my buddies 1990 f250 xlt lariat gasser thats been sitting in his back yard. I was inspecting the brakes and noticed the truck brakes work but only when it reaches the floor with no boost. Engine running or not there is not resistance to assist in braking. I did notice and air hissing leak sound coming from under the steering column in the cab as if a diaphram or seal had torn. My guess is if I had a blown seal or diaphram in the firewall mounted brake booster. I did bleed the brakes and saw no external brake fluid leaks coming from the lines, calipers or master cylinder. So my guess is a bad brake booster. Does anyone else have any advice or ideas what it could be and what should be replaced?
Vacuum leak under the dash..... Do these trucks have a cruise control purge valve under the dash. You know, to let out vacuum from the vacuum servo to close the throttle.
As far as no assistance, booster must be bad. It's not unheard of. But check the hose and check valve to see if they are plugged.
If your brakes were good, assisted or not, the pedal shouldn't go to the floor. Double check for leaks, and maybe look for a swelling brake hose when you push the brakes. Possibly need to bleed brakes more or the master is also bad and not building pressure.
ill check out the swelling hose. as far as the the leak under the dash it is only when i push down the brake pedal pushing the the rod through the cylinder causing a forced air release as if an o ring or seal has ripped and pushing it back out. almost as if its preventing it from applying the pressure it needs to activate the booster resulting in just applying the brakes mechanically. I hope I made sense somewhat.
So i ended up replacing the brake booster and then also realized I needed to get new rotors and pads. But it still is not working as I had hoped, yet the braking is alot better. So my last thought is the master cylinder with an internal leak.