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My camera died, so I'm still working on pictures.
Where is the TCC supposed to lock? Because it's locked in the two higest gears. So, if it's a four-speed and I'm feeling the TCC lock as a shift, then it would need to be using the following shift pattern:
However, I was thinking that the RPM's/speed might nail it down, depending upon the ratios that are calculated...
I have stock tires, and a 3.73:1 rear. With a 31.7" outside tire diameter, that's 99.59" circumference, so 636.2 revolutions per mile. Multiply by 3.73, and that's 2373 revolutions per mile at the output of the transmission.
At 50 miles per hour (0.8333 miles per minute) I'm running 2000 rpms with the "Overdrive off" option activated and the torque converter locked.
At 70 miles per hour (1.167 miles per minute) I'm running 2000 rpms with the transmission in its highest gear and the torque converter locked.
50 mph should be 1977 rpm at the output of the transmission. 70 mph should be 2769 rpm at the output of the transmission.
So, that gives ratios of 1.012:1 for drive, and 0.7223:1 for overdrive. There are some variations in speedometer readings and tire diameters, and we know that drive is 1:1, so we can use that to find a correction factor of 0.9881 based upon the deviation between the calculated and known drive ratios. Applying that to the calculated overdrive ratio, corrects it to 0.7137:1
And that's a lot closer to the 4R100's claimed 0.71:1 overdrive ratio than to the Allison's 0.74:1.
Still too close for comfort, though, unless someone can confirm that the shift pattern is as I described at the top of this post. I definitely want to get a picture.