Just picked up a 1983 f150 4x4 with i'm guessing 160xxx miles becuase of the only 5 digit odometer.

First ford.

Seller said it just needed a new brake booster because brakes were practically useless.

So, I popped a new one in, but get no pressure to the pedal at all even after repeated pressing. However, I did notice that while idling, when I press the brake pedal down (still no pressure), I hear the engine idle speed change.

When looking under the hood I can hear some sort of vacuum/exhaust sound coming from where the brake booster vacuum line connects to the engine.

Trying to get this on the road so I can get to my job starting on the 17th.
Any thoughts greatly appreciated.

 

Sounds like you have significant vacuum leaks. If this is the straight six they are notorious about vibrating the carb and maybe even the manifold loose, so check that things are bolted down snugly. And, all the vacuum hoses are essentially 30 years old and may well be cracked, so look each of them over for signs of splitting.

 

If the booster was bad, then the master cylinder is too. Particularly if the brakes were useless.

Good news is that a master cylinder is cheap and easy to replace on these trucks. Mine was $15 at Advance. Bench bled it while mounted in the truck and now she locks up the tires!

 

Not doubting the master cylinder/lines/wheel cylinders may be shot, but I was definitely hearing noise coming from where the booster vacuum line goes into the engine and its right near the carb and manifold, so when I get off work today, that'll be my first check.

Thanks for the replies so far, I'll be reporting back with my findings.

 

Alright had a second to diagnose things, and found the liquid in the master cylinder to be doodoo brown in the larger spot, and redish in the smaller....

No leaks throughout the system that I could find.

Going to check the back brakes to make sure they are in correct adjustment.

If they are, I will then flush the system to make sure that I've got only nice clear / yellowish brake fluid in there to make sure that i'm not just compressing this other red stuff.

And if that doesn't fix it, I'll probably start with replacing the master.

 

Does that mean you got the vacuum leak fixed?

 

Went through the same thing on my truck. Thought it was air in the lines and bed the back, couldn't get the front bleeder screws out so I figured I'd put on new calipers. New calipers and all new bled lines and still no dice. Paid 15 bucks for the master cylinder, and at the back of the old master cylinder where the snap ring holds the piston in with the hole for the brake booster plunger, the master cylinder was oozing brake fluid like a capsizing boat. The fluid was also nice and muddy like you described (presumably because the PO's probably never changed/flushed brake fluid).

Changed out the bad booster about a 3 weeks ago. It was full of brake fluid and it had to drain for about 15 minutes before I put it in the box as a core.

 

Well, I think it means I may not have had a vacuum leak. I think the engine idle fluctuation via brake pedal was affected by the fact that the pedal was able to go all the way to the floor and thus creating a lot of vacuum in the booster.

From what I've been reading, if the booster was bad, I would have extreme pressure to the pedal.

 

If you mean you would have to put a lot of pressure on the pedal to stop the truck, then there is some truth to that, although I wouldn't call it extreme.

 

Quick update.

Went to start on the brakes this after noon, so I started with attempting to bleed the back brakes, but was getting absolutely no fluid to either rear tire?

Reservoir had plenty of fluid.

The first time I tried pumping the brakes for bleeding the backs, I had the cap off the master/reservoir and the fluid blew out the top. In my thinking, this indicates that the master is creating pressure, and is good? and with the cap back on, should create pressure to push fluid through the lines?

 

The cap doesn't actually contain things to create pressure, but just keeps things from spewing out. Look for a flattened brake line somewhere that would keep the fluid from getting to the rear. If not, crack the hose loose slightly where it goes into the tee on the back of the axle to see if you get fuel there. Just keep working toward the master cylinder cracking things loose to see what you finally get flow. If none even at the MC then it is bad.

 

Where is that Tim Taylor thing.... I should just bookmark it....

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Funny man! I would correct it but then your post would seem out of place so I'll leave it. Let the record show that it should read "flow", as in some brake fluid should come out. (Good catch.)

 

Wow, thanks!

I generally breeze through these posts fairly quickly and this was no exception, I wonder how I detected that....

 

well i missed that mistake

if i were working on this truck, i would condemn the master cylinder just for having all that junk in there. bench bleed the new one (buy new not reman), and then go from there working fluid down the system.
when i changed the MC on a 79 last week, i made it real easy for myself, opened both rear bleeder screws, put hoses on them going into bottles of brake fluid, with the hose end submerged. they make bottles just for this. a combination of pedal pumping (working alone), and just letting gravity work got me there pretty quick. then i did the same thing to the front.

if for whatever reason you don't want to start by changing the MC, then i would start testing for flow at the lines leaving it and work to the rear. i've read several threads about defective rebuilt MCs that wouldn't flow to the rear.

as for booster failures, there are a two common failure modes i can think of, and at least one really weird one i experienced once but have never heard of anywhere else. the common ones are vacuum leaks, and loss of brake assist. the weird one i had would suck the pedal down any time the engine was started, i don't know what internal failure caused that, but it was weird.

as for tracking down vacuum leaks, get yourself a cheap propane torch, the ones that screw onto the coleman bottles. make sure its one that is NOT self-lighting. then, with the air cleaner off and engine running, open the valve on the torch (without lighting it), stick the tip toward the carb and notice how the engine responds. then start moving around to every connection that could leak air, and any significant leak will become obvious in your engine response. of course, this should be done outside, don't want anything funny with propane collecting in your garage and exploding, not to mention CO hazards of running your engine in your garage.