Rebuilt M12 changing quick and not kicking down

Is the electrical kick down solenoid connected and working? There should be a switch on the throttle pedal to operate it, the switch was missing on my car when I got it. It will only kick down when you floor it, otherwise just use manual second when you need it.

They do upshift pretty quickly unless you are really standing on it and will pretty much shift into second as soon as the car is rolling.

I have the M11. When I first had my car, I thought a gear was out because I couldn't detect the shift into second gear at 3 mph. And, it's just so silky smooth. My kick-down solenoid is on a bracket that's mounted to the firewall. Adjusting "the throw" means adjusting the throttle rod, which I needed to do because it was set so the primaries were opening only 2/3 of the way and the secondaries were staying just about closed. No way to rev and let the tranny stretch it's legs like that.. For performance, you'll need to be the Shift Commander and do it manually. I've read on the forums that you can adjust the vacuum modulator by turning in the screw on the inside to let it wind up more. But, not like putting it in first gear and deciding when you want to shift. As for kicking down, I have to completely floor it like Western Red said.

If the shift points are too low and too smooth then there's something not right with the vacuum modulator or the adjustment. Assuming the VM is the correct part number as well as it's push rod ( there's two different lengths ) , then the internal pressure adjustment setting is too low.
In the normal AMC passenger cars prior to 1969 the factory recommended pressure settings were set very low to provide smooth shifts and to get into top gear quickly. These smooth shifts, especially the 1 to 2 shift , have a lot of slippage due to the slow engagement of the front band. This makes the cars seem rather sluggish as the engine never gets up into it's horsepower peak range. It also leads to short life for the front band and for the clutch packs if you drive in a performance oriented way. For performance models like the SC-360 you have to up the trans. pressure settings above those indicated in the shop manual. With a properly performing AMC V8 engine the WOT upshifts should occur at between 4800 and 5000 rpm.

You can up the pressure setting a few turns clockwise at a time and then do a road test. It could take as many as 6 to 8 full turns to get the desired pressure. As the pressure setting is increased you'll find the shift points moving up and the shifts becoming firmer. If you increase the pressure too far you'll find that the upshift from 1 to 2 will be either be too late or it may not shift up at all. Once the 1 to 2 shift point is set properly the 2 to 3 shift point will also be moved up proportionally. Don't be concerned that the higher pressures will shorten trans lifer. It will not, it will increase longevity by reducing internal slippage of the friction elements.

Simply shifting manually to raise the shift points without raising the line pressure will only serve to shorten the life of the transmission.
    
The kickdown or "passing gear" is electrically actuated by a slide switch mounted to the top of the accelerator pedal bracket under the dash. It should be connected to a two wire plug. The plug has 12 volts on one side and provides 12 volts to the kickdown solenoid when the switch closes when the accelerator is at WOT. The switch is self adjusting but it must be set initially by following the procedure in the shop manual. Basically the switch slide is moved with some pressure to the minimum range of it's travel. The internal contacts will "ratchet" into this position. You'll hear and feel a bit of a "zip" sound. Then you floor the accelerator ( engine off ) to move the switch to the WOT limit of the pedal. This tells the internal part of the switch to zip back to where WOT is. The switch is then calibrated for position.

The wire leading to the kick down solenoid should be a single dark blue coming out of the main wire harness that's in the area of the wiper motor. There's a jumper connector wire that connects to this "stub" and leads down to the transmission which has a corresponding electrical terminal up on the side of the main transmission case.

If the kick down solenoid is working you can hear a faint click from inside the transmission when it's activated. Turn the ignition key on but don't start the engine. Have someone floor the accelerator while you listen carefully under the car for the click.

When you have the pressure settings optimized and the kick down working you'll find the tranny shifts quite well. It may very well chirp the tires on the WOT 1-2 shift.

One last word of caution and that is do not drop the car into 2nd gear when trying to slow down. This will stress the front band. When slowing down, typically the throttle is closed which means that the transmission operating pressure will move down to it's minimum pressure. The band and front drum will then be subject to a lot of slipping and heat build up burning off the momentum of the car. Let the brake linings slow the car down, not the transmission.

Also worth noting that the pressure checking details in the TSM are not entirely correct since the BW11-12 has four oil ports rather than one like the earlier transmissions, but they never updated these details in the manual. 

My Tranny guy did tell me he was unable to source a long pin version of the Vacuum Modulator which needed replacing, so he put in the short pin version that he could get hold of.
Could this be significant ?