Information about my truck

My 1977 f100 has had some brake problems ever since I bought it back in december. The previous owner had switched out the brake booster. I know that the truck is heavier than my other cars, and that he technology isnt as good as the modern stuff we have today, but I can tell something is wrong. The brakes do work, but I always drive with a good distance between me and the next car in front of me.

The problems are

A. The pedal travels down about 3/4 inch before I can actually feel it pushing the brake fluid. About half way through the 3/4 inch, I feel a very very slight click almost.

B. Braking feels squishy and requires more brake pedal travel than usual (past the 3/4 inch where the pedal doesnt do anything).

C. Fluid has come out of the master cylinder whenever I check it after driving. I can tell this cause not only the outside of the cylinder is wet, but I see brake fluid actually dripping off the metal

I had bought some brake fluid in order to do a brake flush and bleed, which I think is the cause for problem B. However, all of the brake bleed nipples are rusted on, and would not budge when I wrenched on them. After that I replaced the fluid that was in the master cylinder with new fluid (I made sure that I didnt suck all of the fluid in there out, as to not introduce anymore air into the system). All of this to no avail.

For problem C, I have no idea. The gasket under the lid is fresh and flexible, and the surface it mates against is rust free and smooth.

The truck is currently in the shop because the clutch they put in a week ago was wrong. I have decided once the truck gets back (probably in a few days) to take it to a brake shop, where they have an impact gun, etc.. Also, if they snap the bleeder nipple or break anything its on them and I get new parts! Yay!

After some brief research and looking at things I have no idea about, I think I should replace the master cylinder. Is there anyway that I can replace it with a newer/cheaper plastic one with a screw lid?

ANY help is much appreciated.

Thanks

 

Have you done any maintenance to the brakes? Sound like a combination of air in the system and worn out parts. Don't waste time trying to fix wheel cylinders, replace them. I'd start with new brakes all the way around. And replace soft lines while you are at it. I know this seems like a shooting a shot gun of parts at a problem, but in my experience brakes systems are like rusted links of a chain. Take one bad one out only to find the next weakest link.

 

When you are stopped does the pedal slowly move towards the floor?
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Sounds like air in the lines. I would probably go through and do a complete brake job. A lot of that stuff can be rebuild for cheap if you are on a tight budget.

 

I dont have the truck with me right now so I cant test it. If I remember right, the brakes dont sink in any, they just feel weak when compared to modern brakes such as my 2013 accord

 

You have single piston calipers in the front and drums in the rear.

1) the rear could need to be adjusted to the point the shoes drag and then back off a bit.
2) Are you loosing brake fluid anywhere?

 

I am not missing brake fluid from anywhere other than when it spills from the master cylinder.

 

I think I would check the length of the power booster adjustment push rod to verify it was set up properly when the power booster was replaced.
Have a look

 

Last night I was looking at some master cylinder replacement videos and bench bleeding. Anyone know the original master cylinder bore and thread sizes for the brake lines?

 

The Brake Master Cylinder piston bore size for 1977 Ford F-100s and F-150s is 1.0" with standard sized SAE inverted flare brake fittings for 3/16" diameter tubing 3/8"-24. (FYI) metric 4.75mm brake tubing is also the same diameter as 3/16" tubing. 3/8"-24 fittings brake fittings are usually available individually through parts stores.

 

At least on the '78s the rears have self adjusters which even work sometimes. Find a vacant lot or road, put the truck into reverse, get it going about 20mph in reverse and then hit the brakes hard, just short of locking them up. A few times doing that and your rears might adjust in for a temporary fix. Plan on replacing the wheel cylinders and flexible brake lines just because.