Simple "divide and conquer" test - get that woman who named your truck in the cab, and have her work the pedal, and you slide under the truck with a ruler / tape measure. Measure the movement of the fork at the tip, make sure she's pushing the pedal all the way. Fork movement should be at least 1/2" - 9/16". If it's at least that, then there's a problem "downstream" - fork, throwout, pressure plate fingers, etc. If there's less than that, then you've got a problem "upstream" - hydraulics, firewall, linkage/bushings in the cab.
Here's been my experience, with my '85:
In the cab:
- Pedal box bushings - the shaft going through the pedal box, between the pedal arm and the arm that engages the pushrod rides on a set of nylon bushings. When they wear, pedal action is diminished; if it's allowed to go too long, you'll get metal on metal and the steel shaft will chew up the aluminum(?) pedal box. DON'T let it get that bad. Replacement set is $20-ish at the dealer
- Firewall - see above. See that sheet metal screw pointing toward the camera in that pic. I *THINK* that's one of the screws securing the reinforcement bracket to the firewall. My '85 looks similar.
- Infamous pushrod bushing - craptastic plastic bushing inside the pushrod eyelet. Again, if it wears all the way through, you get metal on metal, and either the "pin" on the arm wears, or the pushrod eyelet does, or both. Not likely to pop out as described above on your truck; our generation of truck has a hole in the pin, and a clip going through the hole, to keep the pin in place on the eyelet. So it'll stay put, but it can get REAL sloppy. The later trucks literally depend on the bushing to "snap" onto the pin, so when the plastic wears, the pin pops out of the eyelet, your pedal drops to the floor, and you have an "oh $#!+" moment. Since we have two of those trucks ('95s) along with the '85, I bought a 1-foot piece of 1/2"OD x 7/16"ID brass tubing, and cut off pieces aprx. 1/2" long to use as replacement bushings for all three trucks. I have plenty more "stock" left if/as these wear.
- Arm/pin/pushrod. Another issue is that the end of the pedal arm shaft, that holds the arm that engages the pushrod, is splined. And when you attach it, and tighten down the nut, the arm sorta "homes in" on one position or another, based on the splines on the shaft and the grooves in the arm. The arm on later trucks is made of a softer metal, so you can position it anywhere you want, and when you tighten the nut, the splines on the shaft dig new grooves into the arm. This is how I get the arm to engage the pushrod in juuuuust the right place on our '95s. But it just doesn't work that way on the '85. The arm is harder metal, so as you tighten the nut, the arm falls into one of the pre-existing notch positions. For me, that meant it was either too "far" (creating an unacceptable amount of free play and having to really mash the pedal to disengage the clutch) or too "close" (meaning the arm is slightly pushing the pushrod even with the pedal all the way up, obviously an undesirable situation). Solution - adjustable pushrod, about $10 at RockAuto.
In the tranny: I found out the fork had been inserted too far into the tranny. The "tines" of the fork were still pushing the throwout properly, but the pivot ball that's bolted to the inside of the bellhousing, just inside of the opening/boot where the fork goes in, was no longer lined up with the "divot" on the fork where the pivot ball is supposed to rest. This made for excessively hard pedal effort, and a noisy squeak. The farmer who owned the truck previously welded the fork, and when he reinstalled it, he probably figured he should just push it in as far as it would go. Nope. You let the pivot ball ride in the divot / dimple on the fork.
In between (hydraulics) - The plastic master and slave were not a concern (I have them on both our '95s), but it was that semi-hard plastic line between them that always gave me the *******. I just imagined the flex in it, absorbing at least some of the pedal action. That was why I opted for the full kit adaptation when the slave blew out. To get the master to mount to the firewall, I had to do the following; referring to TahoeTom's pic above:
- Again notice that sheet metal screw. I had to grind off a bit of the outside of the "base" (bracket) of the master to clear that screw
- See that flange on the left side of the pic (toward the TRUCK'S right from the opening)? I had to grind the edge of the bracket down a fair amount, almost to the master itself, to clear that.
- Notice the bottom mounting hole is closer to the "through" hole than the top mounting hole? I had to elongate that hole downward just slightly, and likewise elongate the hole on the master bracket UPward just slightly, in order for them to line up.
- Finally, the OEM master has studs built into it that go through those holes in the firewall, and two nuts inside the cab secure it. On the '92-up trucks, the pedal box has the studs built into it, so they're sticking out of the firewall into the engine compartment, and two nuts on the engine side secure the master. Once I got the hole alignment thing resolved, I just bought two stainless 5/16-18 bolts, two washers (esp. to accomodate the elongated hole), and two nuts with flange heads, to secure the master to the firewall.
The slave is pretty-much the same, so it went right in. One helpful tip there - any new slave has a clip that holds the slave rod in; it clips to the slave body on either side. The "official" instruction is to leave that on, to ease installation, then the first time you hit the pedal to push the fork, that clip breaks. (Think "*****", or, er, "cherry".) Rather than do that, I installed it with the clip in place, but then unclipped the ends ("ears") from their notches on the slave body. Slave works exactly the same way, but now I have the option, if I ever have to remove the slave again, I can re-clip the clip to the slave body, and when I remove it from the tranny, the rod will be held in place. Pushing that rod back from an uninstalled slave, after it's been extended, is REALLY hard, and in fact, trying to push it back was how I blew out my old slave.
So, excuse the "drink out of a firehose", but hopefully there's enough there to give you some things to try.
