I have a 78 f150..today when i cranked up my truck the brake light wouldn't go off...so I pumped the brakes for a couple secs and it went off.. Then when driving the brakes went spongy..brakes still worked but spongy...and couple secs later it was back to normal... I visually expected all my brake lines..they all looked fine.. I inspected my brake shoes in the front and plenty of pad...I have not taken off my drums in the back yet but plan on doing it tomorrow..

I did see this tho...I dont know what it is..




It is leaking..very slow leak...but I do not know if it would account for the problem I had today..

I also checked my brake reseviour and it was full.. im guessing I need to bleed my brakes?? anything else I need to do?? Is it safe for me to drive??

 

Could be a bad master cylinder, leak in picture above could be the switch that's screwed in the top of the proportioning valve, a very common problem with Fords. The switch is still available. Also check the rear brake adjustment and look to see if the rear wheel cylinders are leaking.

 

By the amount of fluid around the p. valve, I would suspect the m.cylinder is leaking onto it. With a good light in hand, wipe a finger on each of the b.lines coming out of the m.cylinder, and between cylinder and booster, and see if there is a drop.

If it is the p.valve, they run over $200 for replacement. But you can get an after-market adjustable p.valve for about $50. If you go that route, it means replacing the line to the valve.

Spongy brakes mean air in the lines. Healthy brakes--without sponge feeling--don't get spongy for no reason. You need to find where the air is getting in, and the fluid is getting out. Have a friend pump brakes, with engine running, while you watch with a flashlight, each of the line fittings on the p. valve.