Another question for the gurus....

Installed the power brake booster and master cylinder off a parts truck (same year) into my '80 which had MANUAL (oh, the humanity..) brakes from the factory.
Bled 'em all 'till I got no bubbles and nice, clear fluid and gave her a spin. Dang near't sent me through the windshield, they did! Yay!

- then I drove it to town about 7 miles up. Beauty. But, on the way home - about 1/2 way - I had a drag and knew right off a caliper (or the pair) were hanging up. They were. Let her cool a few minutes and managed to get home.

Now: Question is, would any one know if there were two different part numbers for the proportioning valve for manual and power brakes for '80?

And any ideas for other possible causes? I need to get her rolling THIS weekend, as I have few left before her yearly trial-by-fire. (an overloaded trip of 250 miles E/W towing a beast of a springless trailer..)
It felt perfect on a couple runs up and down my side road, and even then up into town. Just on the drive back that she gave me the fits. Calipers have MAYbe 2000 miles on 'em too. New flexy lines up front same time.

Cheers!

 

I dunno if the proportioning valve is different (doubtful, but possible), but if you installed a used master cyl, it could be the cause of the brakes dragging. Particularly if it sat unused for a while......

 

As shown below, all 80 to 83 below 8500 GVWR use the same brake pressure differential valve.

 

Your problem sounds like the compensation ports in the master cylinder are covered. This is simply caused by the pushrod coming out of the booster is too long and pushing on the master all the time. Or since this is a conversion, maybe your linkage to the pedal is not right and pushing slightly on the booster.

Take a look at the pedals. Is the power brake pedal and arm the same as the manual one? I didn't think they were, the hole/pin may be in a different place on the pedal arm.

 

The manual brake pedals are different from power pedals. I don't know what the differences are, but they are different.

 

Wow! Thanks fellas!
No way to check on the donor trucks' pedals - it's likely already been made into about 7 Focuses or lawd knows how many Kias..
But the pushrod idea may have a heap of merit. Now to figure out how to shorten *that* without mucking something up... Wonder it it's adjustable? I just did a direct swap - out of one, into the next.
This thing needs to be good today - AFTER coffee, of course...

 

I would check this first. This is the spec on how far out the rod on the booster should stick out from Autozone's site. DON'T PULL THE ROD OUT OF THE BOOSTER. You should be able to loosen the end and adjust the length after you pull the master cylinder off.

The push rod should extend past the face of the booster as follows:

1976: 0.880-0.895 in.

1977-81: 0.931-0.946 in.

1982-86: 0.980-0.995 in.

 

Usually with other vehicles, the manual brake versions have more ratio or leverage on the pedal geometry. This gives you more advantage when pressing the pedal, but the drawback is more pedal travel. They do this by moving the pin or hole up higher on the pedal arm. The power brake setup needs less advantage at the pedal, so they usually move the pin down closer to the pedal pad. A lot of them you will see the master and the booster angled a little bit because of this.

I am still not sure if that's the case on these trucks, manual brakes are pretty rare during these years.

 

GEEZ-o-petes!
Thanks guys!
I broke out my old Auto-tech manuals I haven't cracked in over 30 years and found the adjustment. Didn't know the length tho, so guessed at it and cranked her in about 3/16" or 1/4". If not proper after a town run to test it, will re-disassemble and give it a gauging to your specs there.
Man, I hope this is all there is to it. And yup - quite the angle on the rod-to-pedal rod. But it was working and I have proper brake lights. Just this hang-up problem.
OK, road test! I spotted gas for $3.39 in town, gonna to give her a fillup so to also test the replacement carb I bolted on the other week as well. Well, *if* the brakes aren't still dragging.

Maybe next I'll replace the busted 3-on-the-tree column with the one I nabbed off the parts truck with the new shift collet and replace that damnable crappy Hurst floor shift conversion someone dropped into it...

Yo!

 

I think manual brakes were F100 only. F150 and up got power as standard.
Not positive, but I believe this was the case even back in the 70's.

The parts list above shows F100 only on the manual brake pedal lines.....

 

Yup. That's the way I read it,

 

Disc brakes were introduced in 1973 F100 2WD. 1973/83 F100 2WD: Manual disc brakes were standard equipment, power disc brakes were optional.