Okay, I need some help here. last week my wheel cylinder was leaking so bad I could hardly keep fluid in the mastercylinder. I picked up a wheel cylinder, bled the line through the bleeder valve, and it was back to normal.

So, I drove it for a day and then went to drive and the pedal went to the ground, kinda spongy, and nowhere's near the brakes i had. I have figured that my master cylinder has been getting tired for a little while, the pedal has been going down a little ways before catching pressure. So I put a new master cyl in, bench bled it, and bled the lines. Still spongy. Took it back at part's guy's request and picked up another new one. bench bled it, still spongy. I bled the lines forever, and it still will go to the ground without stopping.

I vaguely remember something about a valve or some other step to take when bleeding brakes on these trucks, and I cant remember what it was. Am I forgetting something major? I'm not loosing fluid, so I doubt it's a leak. Any suggestions appreciated. The rig's a 76 F100 with power brakes and disks up front. THANKS!

 

I don't know but it sounds to me like you still have air in the line somewhere. Does the pedal stiffin up if you pump it a few times?

 

not really, no. It still just sinks. after talking to Beeboy and Monsterbaby online for awhile, I'm realizing that I was never formally educated in bleeding brakes, just the redneck try-it-and-see-what-happens training. SOOOO.....

If I leave the bleeders open between pumps when bleeding, will it suck air back into the lines??????

 

in my primitive knowledge of brakes, i know you have to close the bleed valves after you put the pedal on the floor, or else you an't doin it right....so, *open, pump to floor once leaving pedal on the floor, close, release pedal* (repeat as needed for a few more times, or until no air comes out of lines, i bleed froma hose onthe bleeder valve into a jar of brake fluid) you need 2 people or else you can't really do it right at all....good luck

 

yes it will.

 

also, if the master cylinder has been replaced, when you are absolutly sure that you've got all the air out of the system and if you still have "free play" in the brake pedal like a clutch pedal, pull the master cylinder off the booster and adjust the booster pushrod. Back the enclosed nut off a little and then retighten the locknut (if there isn't a locknut, just use blue locktight on the hat nut). reassemble and repeat if nessesary. The exact spec is .980" to .995" from the booster surface but that won't REALLY help if a rebuilt master has been swapped on at some point in the trucks life.

BTW: the valve you heard about is only on a few 79 proportioning valves.

 

bob is back! no more old ford iron

 

If you don't have an assistant, you can fill a jar with clean brake fluid, attach a vaccuum line to the bleeder screw, and put the other end in the jar of brake fluid, and pump the pedal slowly. The fluid in the jar will keep any air out of lines, and you won't have to have a helper open and shut the bleeder every time you push the pedal. Also, you are starting at the right rear corner and going to left rear, right front, and left front, correct? You're not letting the master cylinder run out of fluid while you're bleeding them are you?

 

FIXED:

Got thinking, and Jim remindered me that usually when you have a problem it has to do with the last thing you "fixed." Take neutering for example, but lets not get into that.

Well, I realized that the brakes worked after I put the wheel cylinder in, so I sort of wrote off the brake as far as having any potential problem. Curiousity and frustration ended up getting to me though, and I took the wheel and drum off to check anyhow. Realized that the day after I put the wheel cylinder in, I took the drum off to make sure there were no leaks. Right before I put it back together, brooke (who was sitting in the cab) pushed the brakes. No biggie, except that I didnt notice the boot adjusting screw fell out.

So, the boots were about touching on the bottom, and the entire motion of the brake pedal was being used to fill the master cylinder. Problem now solved (i'm a tard, tired from a long day, and gotta wake up early for school, but at least I have truck now) brake's tighter now than ever

 

I was wondering if that fixed it. Took me awhile to find this thread since it migrated on its own out of our chapter

 

Yup. Mitch says he's stealing your vacuum thingy to get the air outta his lines, otherwise i woulda had it sitting at your house already. Thanks for the help with that though

 

I'm having a problem understanding this.

It would seem to me that when the brake pedal is released it would suck fluid back in as you say, but then you would just push the same fluid back out when the brake pedal is pressed. The flow would be back an forth. In order to bleed the brakes effectively wouldn't the flow have to be one way to push fluid and air from one end to the other?

 

yeah usually this will leave air in the line somewhere. You have to close the bleeder.
if your doing it alone you need a pressure bleeder, a vacuum bleeder or those fancy easybleed bleeder screws with a check ball in them.

 

Oh great, I might get it back by Christmas then