You're absolutely right, Paul. Depending on the condition (wear, bends/kinks, etc) of your shift cable, there is lost motion (hysteresis) when changing directions.
Picture this: You have a 3 foot long piece of 1/2" heater hose, and you have a piece of small diameter (1/8") wire rope inside the hose. The hose is laid out on a table in front of you in the shape of the letter "U", with the open ends pointed toward you. If you pull one end of the wire rope toward you 1", the free end of the wire rope moves away from you just about the same amount. Pull another one inch, and the free end moves away another inch.
Now push the wire rope away from you 1". The free end of the wire rope moves little, if at all. Your 1" motion has been lost inside the hose as the wire rope moves to the outside of the "U" shaped bend.
This is an extreme example, but exactly what happens with any push-pull type of cable application. This is the reason for the "rooster comb" on the manual valve lever - basically we get it close with the shifter and cable, and the spring and ball force the rooster comb to precisely the same place every time. Unless of course, your cable is sticky, corroded, kinked, etc. and won't allow the manual valve lever to move that extra small amount.
Having fine threads and adjustment holes at 60 degree increments allows length adjustments of as little as .007" per hole, so finding that perfect spot is ensured, again, depending on the condition of your cable. And again, as long as there is not significant friction in the cable, close enough is usually close enough.
So if you're having a problem getting a '62-65 shifter adjusted properly, first check the entire system for lost motion. The shifters (pushbutton, console and column) are very robust and seldom the cause of problems (despite what you'll read other places), but any attaching points of either the inner member or outer housing can cause issues.
Starting at the shifter end, check the fit of the eyelet on the shifter pin (not usually worn but sometimes the wrong cable is used), the fit of the bayonet "pointy end" into the adapter, and the fit of the adapter into the manual valve detent lever (often incorrect if parts have been swapped or modified). Also ensure that the eyelet and bayonet are securely crimped to the wire. Check the housing mount where the shifter (or bracket in the case of pushbuttons) is crimped to ensure the connection is tight and there is no movement. For pushbuttons, make sure the bracket is tightly screwed to the pushbutton unit. You can use a thin nut inside the pushbutton housing in the event of stripped holes. Then check the integrity of the crimps at the upper ferrule and the adjuster to be sure the housing isn't sliding in and out as the cable is moved. Finally, check the threaded adjusting wheel to ensure there is no significant motion at the threads (there will be a few thousandths) and that the wheel is securely attached to the transmission case.
Last, if your transmission has been rebuilt or repaired, be sure the manual valve detent lever spring is of correct size. Very few transmission shops have the correct spring, and since the original spring is very light (we are, after all, shifting with plastic pushbuttons), technicians often replace the spring with a heavier one, as it's obviously "better". Too heavy or long of a spring requires additional force to move the detent lever, resulting in bracket deflection, loosening of crimps, or accelerated cable wear. In extreme cases the inner member will kink. I tshould take very little pressure to move the manual valve lever, unlike the '66-later models.
The bottom line is that the pushbutton shift system (as well as the console/column variants) is very robust and dependable. Stories of adjustment horrors are always the result of worn, damaged, or incorrect parts. Like the ball and trunnion, pushbutton vintage shifters get a bad rap because they are different, and many would rather swap them out than learn about them.
That said, some of the other manufacturers that used pushbuttons definitely gave pushbutton shifters a bad name!
SC
My 2 cents: I have used the FSM method, test light method, Ohm meter
method, and eyeball method. What I found was that there is a little
inaccuracy in the shift cable mechanism. If you line up the neutral detent
with the neutral safety switch by eye it will be close. However you need
to use the push buttons to shift the mechanism a few times to see where
things will "land". Most of the time it will be off slightly. You can
then use the wheel to fine tune things. An analog type Ohm meter is then
helpful because it will show if you are slightly off by showing varying
levels of resistance as you adjust it in and out. The test light will work
this way as well with the light getting brighter or dimmer as you home in
on the sweet spot and the neutral safety switch makes good contact.
Paul L.
Back to the Home of the Forward Look Network