hey ive been having problems with my brakes on my 1980 ford f100 4.9l.
when i first got it the brake pedal was really soft like i had to push it all the way to the floor to get the truck to stop. and also if i pumped the brakes like 2 times before i stoped it would stop fine. so i bought a new master cylinder, bench bleed it and everything and i was still having the same problem. so i figured the brakes needed bleed so me and my dad bleed the breaks today and they were working fine for awhile then i drove about 10 miles and the brake pedal started to get really hard and i dont have to push it down much to get the truck to stop. im thinking its the brake booster but im hoping i dont have to buy a new one. and also the brake pedal sounds like a hand pump when i push it, like i can hear air like if you was pumping a hand pump to a bicycle. its been doing that ever since i got the truck. thanks for any help

 

It does sound like the brake booster to me.

 

Sounds like the booster to me too.

Just replaced the one in my Bronco last Saturday. The new booster cleared up a couple of strange issues I was having...stopped WAY too easy, and locked up if I wasn't careful in the mornings.

New booster and a complete rebuild in the rear, and it's stopping like brand new.

Thinking I'll have to do the same to the F-150 soon.

If you want a temp fix, go to the JY and get one there for like 10 buxs.

 

thanks for the help!
yeah i figured it was the booster i just wanted to see what other peoples opinions were.

 

well i got a new booster today and put it on and now the pedal goes basically all the way to the floor and barley stops the truck. we bled the brakes several times and its the same thing. and also its seems that the brand new master cylinder is leaking from the top like the from the cap. any ideas on why im having this problem?

 

- With the engine not running, can you pump up the brake pedal at all?

- Assuming you can pump up the pedal as above, push down on the pedal, start the engine, what happens to the pedal?

- Disconnect & plug the vacuum line from the booster, tell us how the pedal feels at that point.



As for the leak, I'm gonna guess that happened while bleeding the brakes? If you pump the pedal while bleeding the brakes with the cover removed, you will oftentimes see little fountains of brake fluid spraying from the open top, could that be where your apparent leak is from?

 

yes i can pump it up with the engine off and when i hold the pedal down after pumping it and then turn the engine on the pedal with go down. i havnt disconnected and plugged the vacuum line yet but i have disconnected it just to see if there was vacuum and there was. and i thought if you plugged it the engine would die? thanks

 

No, the engine shouldn't notice if you disconnect & plug that vacuum line (assuming you do it while not running); if it *does,* that's a pretty good indication there's a severe vacuum leak in your booster, combined with the engine being out of tune.

If the engine needs the extra air from a vacuum leak to stay running, something is very wrong there.

In any event, it sounds like you have a defective booster.

 

alright ill have to check it in the morning.
and when we bled the brakes we had the cap on the master cylinder i noticed it dripping from the bottom after i got back from driving it around the block and i then noticed it was coming from the cap and running down it dripping from the bottom. and both master cylinder and booster are brand new not remanufatured ones.

 

Man, I hate it when that happens...spend an hour installing a "new" part, just to have it fail like that.

Seems to me that the part store that sold it should not only replace the part, but pay you for your lost time and effort.

Damn cheap *** chinese junk....

 

http://www.autoshop101.com/forms/brake05.pdf
Troubleshoot Power Brakes

Both of those links will explain in agonizing detail how the booster works, it's basically just a diaphragm.

That's too bad that a brand-new part is defective like that, but it happens sometimes.

 

thought id let you guys know that i fixed my brake problem, the rear brake shoes were basically gone nothing left of them like i jacked it up had my dad spin the tire and i hit the brake and it didnt stop it. so i got new brake shoes put em on and now the truck stops perfect!

 

Um, I'm kinda confused.

You didn't pull your wheels off first, before assuming booster (or any other) problems? I think a lot of us here might of not suggested your booster if we had known you hadn't even pulled the wheels off to look at the pads/shoes.

I, for one, would not of taken the chance of insulting another user here by by asking a "duh" question like "did you pull the wheels and inspect your shoes and pads?" I guess I wrongly assumed you would of already done that. My bad.

We gladly help anyone that asks for help, but it helps us when you do the basics first. If you don't know what the basics are, then let us know that so that we can get you the help you need.

In your first post you outlined all the work you did, and the parts you had bought, to address this problem, right? You did all that without even pulling the wheels?

 

when i got the truck from my grandpa he told me it needed a new master cylinder and prolly a brake booster as well so i went with what he said and bought a master cylinder and it didnt fix the problem but it needed a new one, we bled the old one to see if it was even pushing fluid threw it and it barely came out the front hole. so then since that didnt fix the problem i bought a booster cause my grandpa said it prolly needs a booster which it did need one with the old one it sounded like a hand pump to a bicycle every time i hit the brake so then after putting that on it still didnt fix it so i pulled the wheels and it needed shoes and it prolly needs wheel cylinders but i havnt replaced those yet.