written by Larry Cleeton (firstname.lastname@example.org)
The GM Supermatic trans controller supports manual up/down electronically, but as usual the Chevy Performance documentation was quite sparse. It describes the wires, but not what to do with them. I knew the dual calibration selector was simply a digital in signal to the controller that you ground to select calibration B. I assumed the manual shift enable/up/down wires would be the same but wasn’t sure. I finally found the answer deep in the Help part of the calibration program you can use on the controller via a USB cable. Of course the old program wouldn’t run on 32 bit Windows. Fortunately Chevy Performance has a download of the latest version that supports 64 bit Windows. Then I found that the program won’t start without being connected to the trans controller. After that I finally found in the program help the following:
2.2.5 Cal A/B Wire
This wire is part of a 4-way connector using terminal “B” of the connector. A neat feature of the TCU is the ability to change to a completely different calibration at the flick of a switch. This is accomplished by hooking this lead to a dash/console-mounted toggle switch. Run the other switch pole to a ground. The default position (off) will be the Cal A setting. When switched on (grounded), the TCU will change the TCU to operate from the Cal B calibration.
NOTE: The TCU is already pre-programmed with an “A” and “B” calibration. The only difference is higher line pressure (firmer shifts) in the “B” calibration verses the “A” calibration.
2.2.6 Manual Shift Connector
The TCU is configured such that it’s possible to have fully manual upshifts and downshifts at the flick of a switch like a bump stick. This works by first activating the manual mode with one switch to Terminal C. Once activated, the transmission can be bumped up (Terminal B) or down (Terminal C) through the forward gears via an On-Off-On momentary rocker switch.
- Terminal A (brn/white wire) – momentary ground for bump down
- Terminal B (brn/lt.blue wire) – momentary ground for bump up
- Terminal C (brn/red wire) – Toggle switch to ground to activate manual mode
Caution: Be aware that serious engine damage could occur due to over-revving if downshifts are made at too high of vehicle speed. The TCU cannot override your input while in the manual mode.