i'm new to these trucks so i don't know if this is normal.
here's the symptoms:

truck normally didn't make that air-hiss sound unless i stepped on the brake pedal. however, today, it started hissing constantly and the hissing actually is reduced when i step on the pedal. when the pedal is released, it goes back to hissing loudly.

any ideas?

 

relax . . you have a bad brake booster. welcome to the elite club lol
basically, the big round thing behind the master cylinder up against the firewall.
good news: easy to replace(four bolts on firewall inside/under dash and two under the hood) also, not expensive at a junk yard -these rarely go bad so you should have no problem finding one that is working fine. also, any from 80-86 will work. even later years im pretty sure.
bad news: not repairable -just stick to the junkyard and pay under 20 bucks for a used one or go to an autoparts store or a rebuilder and pay upwards of 80-90 bucks for a rebuilt(its up to you really).
no more bad news really. its pretty simple if you are into fixing up your truck on your own.
good luck hope that helps

 

I'd spring the $30-50 bucks to get a new one and never worry about it again.

 

While checking out your booster, check out the vac line to it. If the end is stretched or cracked, etc could also be loosing vacuum. Some people cut off the last inch if it is bad ( provided it's long enough), but it is better to just replace it. I've had old vac hoses so bad that they leak in the middle as well as the ends!

 

thanks guys.

is this an emergency part? i.e., how long can i put this off before something bad happens???



i'm new to the whole ford thing and it seems everything i read is about vacuum lines.

under the hood, there are about 20 rubber lines. some are disconnected and plugged; i believe they went to the old pollution control carbon filter.
are all those rubber lines (except the gas lines) vacuum lines?
sheesh, there's 3 or so that go to the air filter/carb. setup.

what a bizarre design. is there a way to plug and get rid of some of them?
seems like a big achilles heel type of setup.

VW beetle = 0 vacuum lines
e30 bmw = 0 vacuum lines
1980 ford = at least 10 of those babies. what gives??

 

if the booster goes out completely you will lose the boost for your power brakes.Then you will have standhard brakes.

 

If you drive this truck very much, I would spring the cash and go get a new one, and I would fix it as soon a possible. Not having power brakes could be a bit of an incovience in the wrong place at the wrong time. I.E. Quick Fast Stops probably not an option!

 

I had an F250 for a short time that had a good running 351W in it. ALL the vac lines were plugged/gone except for the vac advance to the distributor and the brake booster. I suppose this sounds like a good ahead for removing, but I am NOT advising that.

Engines are designed/tuned to run with all the "extra junk" operating. As a novice (me), I would just check for leaks 1 line at a time and learn what I can about each device. I've heard a number of stories claiming better and worse performance after removing lines. The hoses aren't expensive and it is easier to get help when I need it if everything is standard.

Good Luck!

 

my 84 has been like that for about 5 years but i don't drive it much think i'll replace brake booster this spring

 

well, i'll add "Check hoses to brake booster" to my list of tasks this coming weekend.

i'm going to be replacing front right bearing, replacing tranny mount, flushing tranny, drilling/cutting rivets in radius arms and installing bushings, and adjusting the timing.

gonna be busy.

i checked at the parts store today for prices on brake boosters.
they want about 70 bucks for one with a lifetime warranty.
they come with and without a master cylinder attached.
if/when i replace it (if it's not just a bad vac line) would it be advisable to replace the master cylinder at the same time?

what type brake fluid is best on these trucks?
I have some VALVOLINE synthetic that says on the label
"exceeds dot 3 and dot 4 specifications"
any problems using it?



thanks.

 

Yeah, my 86 F150 had the brake hiss problem. The booster is easy to install. It's a little bit of work to get the old one out, cause it's sort of glued to the firewall.

The only thing to be careful of is the master cylinder. I just unbolted mine from the booster, and it tilted back to a 45 degree angle, which let air into the master cylinder itself. It's kind of a pain to get the air back out. So, if you do end up switching the booster out, try to keep the master cylinder level to avoid air getting into it. Other than that, the hissing is gone.

 

ooohh.. good tip.
wouldn't have thought of that .

thanks very much.

 

back to this brake thing again.
it's not the vacuum line.

local discount auto parts wants $90 for a brake booster! sheesh.
anyplace i can find a cheaper one?

my only other question is this:

how do i know if i need to replace the master cylinder at the same time?
all the brakes work great and the system has been flushed recently.
is this a good time to replace it "just cause?" or is it pretty easy to do as a separate procedure?

thanks.

 

i would replace it just cause -mr moneybags- lol if you want to go the cheap route go to the junkyard like i mentioned before. it will cost you 5-20 bucks for a new booster and another 5-15 for the master cylinder. if it doesnt work you just get another one uf the place has a warranty like the ones here and if not, try your luck again and buy it all again. lets say you spend 40 bucks in total . . still less than 90 bucks but you are chancing not only whether it will work then, but for how long. its up to you. [offtopic] by the way, i forgot to ask in the other thread, how much for the kit you bought?[/offtopic]

 

front wheel bearing (inner/outer races and cups) and the locknut and adjustment nut plus both sides energy suspension radius arm bushing kits plus tranny mount and 3 quarts of gear oil came to $89. everything has a lifetime warranty according to discount auto parts here in town.

pretty nice seeing as how just 1 sealed front wheel bearing for a 1985 bmw 318i costs about that much.

...and no moneybags here. i'm about 10 classes from graduating with a mech. eng. degree and have been working my way through school. i'm quite used to abject poverty by now.


in fact, that's what got me into working on cars to begin with... i HAD to because i can't afford anything else. works out well though. it's good practical, money-saving experience and quite satisfying when you get something fixed.