I have a 1986 F-150, HO 351W, C-6 auto, 9inch rearend. RV cam, trams has a tag on it from Jasper Engine/Transmission, Jasper, IN, some light mods to the trans... edelbrock 4bbl carb. Truck was given to me a few Christmas' ago so that is all the info I have on gear.

Wife and I were driving around a week ago and my brakes would go to the floor sometimes after sitting at a stop light. By the time I was home I had no brake booster at all, truck acted like it had manual brakes.

I replaced the vacuum booster, still no brakes. Replaced it again just in case it was bad, no joy on brakes. Realized the left front caliper was frozen so went ahead and replaced it, can gravity bleed all four corners. As a last resort replaced master cylinder also.

Still not able to pump up the brakes to do a final bleed. vacuum lines look good, since the truck sat for 5 years before it was given to me, figure replacing them with fresh vacuum lines is always a plus. I will be doing that this weekend. I also noticed an escaping his from the vacuum line that attaches to the brake switch...not sure about that one either.

Any thoughts would be helpful. You can email me or text me either way is fine. Need some advice from someone that has experienced this before if possible....

 

It sounds like either a bad master cylinder, or a vaccum leak...

 

Master cylinder is new, will be looking at all vacuum lines tomorrow but with the vacuum tester they look good initially.

 

The hiss at the brake pedal is vacuum for the cruise control. Replace the rubber line. You need to bleed the brakes. gravity bleed? Have someone pump the pedal, then hold it while you open the bleeder on lrear wheel. They hold it to the floor untill you close the bleeder. pump it again, and hold it while you open/ close the bleeder. Do this untill all the air is gone. Put brake fluid in the master cyl frequently, as to not run out. Move to r rear wheel and repeat. Move to thr r front wheel and repeat. Move to lfront wheel and repeat. If brakes are still spongy, find, and repair the leak, then bleed again

 

Problem ended up being the brake booster. Every one that I would get from O'rielly's would be bad. Bought a brake booster from Autozone and everything is great. Now the only item that is not new in my brake system is the lines. Solid now.

 

By the way I appreciate everyone's input. It is helpful