03/11/2018
Someone asked if it was possible to manually disengage the clutch by pushing on the end of the clutch fork. Here was my response. I'm thinking of making it into a full tech article.
Ok, so here is a little clutch 101. Bolted to the flywheel is the clutch cover, this is spring loaded and presses the clutch disc (the disc is splined to the input shaft of the transmission) against the flywheel with a great deal of force. The clutch functions much like a disc brake, but with a great deal more surface area, and it operates in reverse (it is normally closed, pressing against the flywheel, unless the pedal is applied, whereas pressing a brake pedal closes the brake caliper).
It takes a fair amount of force to overcome the springs in the clutch cover and release the clutch. To do this while the engine is turning (and thus the cover) requires a throw out bearing which the input shaft passes through. In some modern cars this bearing may be one piece with the clutch slave, but on yours there is a lever or fork, which pivots on a pin or axel on one side (it's a second class lever), holds the throw out bearing about halfway along it's length, passes out through the bell housing (through a boot), and attaches to the clutch slave pushrod on the end that hangs outside the bell housing. The lever obviously provides some mechanical advantage. Also, some endfloat (or endplay or slop) is required to prevent the throw out bearing from prematurely failing due to prolonged contact with the clutch cover.
When the pedal is pressed, the pedal (which is a lever) multiplys the force from your foot before pressing in the master cylinder pushrod (I measured 8" from the pedal pad to the fulcrum, and 1.75" from the fulcrum to the master cylinder pushrod for a ratio of 4.57143:1). The master cylinder is a different size bore from the slave. The best info I can find say the master is either a .70" bore or a .75" bore (pi*r^2 gives a cross sectional area of 0.38485 or 0.44188 square inches), but the slave at 7/8" is going to be .875" (giving a cross sectional area of 0.60132 square inches. That means there is even more mechanical advantage just going from the master to the slave (the force at the the master cylinder being multiplied by a factor of between 1.36082 and 1.56248 depending on which bore measurement is correct).
Multiplying the two ratios together (pedal and hydraulic mechanical advantage ratios) yields a mechanical advantage of between 6.22089:1 and 7.14277:1 at the slave pushod. I don't have a clutch fork from a 1500 to measure, but from pictures, it looks like it's pretty close to a 2:1 ratio. In short, the throw out bearing is moving either about 1/12th the distance that your foot moves when pressing the pedal to the floor, while applying 12 times the force, or 1/14th the distance while applying 14 times the force. I don't know how much pressure is required to depress the pedal on a midget (don't have the means to measure it), but one website gave 35lbs on a Ford ranger, and having driven one with a manual I'd say it feels similar enough. So basically you'd be looking at between 420lbs and 490lbs of force at the clutch cover, or 210lbs to 245lbs of force at the slave pushod to get the clutch released.
Again, there will be a little free play at the throw out bearing to make sure it doesn't always touch the clutch cover and wear out too fast. This endfloat will of course be doubled at the end of the clutch fork. On my car which has the Datsun 210 5-speed installed, there is a lot of play at the top due to a worn pedal and clevis pin. The first inch and a half to 2 inches are required just to get the throw out bearing to touch the clutch cover. From there it's roughly another 2" at the pedal to get the clutch to just start to disengage, and the pedal moves only about 5.5" from rest to the floor (and it's normal for the clutch pedal to go to the floor btw).
This means that once the bearing touches the clutch cover, that slave pushod has to move roughly another 1/3" to start disengaging the clutch, but to fully disengage it, it may need as much as a half inch. Of course all of these calculations are rough estimates based on educated guesses and rounded numbers and rough measurements, but they should give you an idea of what is going on and what you are up against.
Long story short, while you could easily move the end of the clutch fork manually up to the point where the bearing touches the clutch cover, unless you are able to safely apply 245lbs of force at the end of the clutch fork, you won't be able to move the fork far enough to disengage the clutch.
