For mad skids the best cars are manual. Manual Commodore’s are not common or cheap second hand. The only option is to try and make the standard 4L60E transmission behave more like a manual.
There are lots of references to ‘Shift Kits’, with various levels of manualization, however, these cost money, and are quite intricate to fit. It must be said however, they would offer a much higher degree of reliability and strength for a road car.
We all have backgrounds in electronics and mechanical systems, so the sometimes daunting PCM (Powertrain Control Module) service manuals were consulted along with websites and forums in order to conclude that the 4L60E was completely controlled by the PCM for gear changes and general gearbox operation.
Understanding the 4L60E transmission is a complex task. It is an awesome piece of modern engineering, however, in its essence it is a gearbox with a hydraulic control system. The hydraulic control system is what the PCM controls to select gears, and lock the torque converter.
Using our backgrounds in electronics we derived a method for ‘manualizing’ the automatic gearbox, that is, electrically controlling the gearbox in order to select the gear we require, and remove any automatic (kick down, shifting and torque converter lockup) functions from the control of the PCM.
When researching the possibility of the transmission manualization, forums such as http://forums.justcommodores.com.au/ were used, however no really useful information was found. Mostly speculation and opinions, rather than fact were given.
Google did offer a glimmer of hope. http://www.msgpio.com/manuals/mshift/wiring.html is a site that is based around the “MegaSquirt” ECU (Engine Control Unit) and the “MegaShift” is a option that can be fitted in order to achieve a manualisation for a “MegaSquirt”. It appears to be a very versatile product, and quite capable. However, we don’t have a “MegaSquirt” ECU nor the money in order to build or fit one. The information on the web page however is very relevant to the aim of this modification, i.e. it details the switches, sensors and requirements of the electronics of the transmission.
Again, using the information in the service manual, and the above websites, we managed to come up with a simple circuit that can not only eliminate the PCM control of the transmission, but allow selection of 1-3 forward gears as well as a torque converter lock. Below is a diagram showing the wire colours and components used in the modification.
Originally we were going to ‘test’ the idea by disconnecting the plug from the gearbox and inserting a plug salvaged from the wreckers, which was attached to a test circuit. We quickly gave up on this idea when we realised the clearance of the transmission to the chassis and exhaust. The alternative was to intercept the signal before it got to the PCM.
Luckily for us, the wire colours were continued to the PCM, and the location (Passengers Kick panel) and PCM connector numbering were freely available on the Internet.
The wiring was cut and a terminal block inserted for all of the Hydraulic Solenoids and range switches. The Speed Sensor and Temperature Sensor were left untouched. The terminal block allowed the connection of the above components.
In keeping with the budget build, the terminal block and components were insulated with tape and covered with a floor mat. (Properly dodgy)
The torque converter and ‘lock up feel’ solenoid switches were connected to a DPDT switch and mounted in the dashboard, in easy reach. They engage at the same time.
The required PWM signals for certain solenoids was ignored, rather a resistor added in series , to reduce the average current.
Starting the car is pretty much the same. Park or Reverse is require to start.
Park, Neutral and Reverse are pretty much the same as standard when the torque converter is ‘Open’, however ‘Locking’ the torque converter in reverse, without speed is equal to dropping the clutch in a manual car, and can stall the engine if the power is not sufficient.
The fun begins when you select a forward gear.
1-3 with the torque converter in ‘Open’ behaves like selecting a gear in a normal automatic, with the torque converter ‘slipping’ to allow the engine to idle. If the torque converter is ‘Locked’ when stationary, the engine stalls.
Applying throttle is like trying to take off in a manual of equivalent gear, that is, if you try and accelerate in 2nd or 3rd, the car is sluggish (the torque converter still reaches its stall speed, (so it’s more like riding a clutch). However unlike an automatic, the manualization does not allow the gearbox to downshift if full throttle is given.
If the torque converter is locked, the engine RPM drops and matches the car speed. The locked torque converter allows a more manual feel to the throttle control. It is the closest thing to a real manual gearbox for throttle control of drifts and burnouts.
The electrical mutualisation of the gearbox has transformed the way the car performs in the extreme situations it was not designed for. The stock car shifted gears mid drift, gave sluggish performance and was generally not performing well for a paddock basher. Manualizing the gearbox has allowed us to utilize the engine and transmission in a more manual fashion, giving better control of drifts and burnouts.
The PCM does not like being removed from it transmission. We believe the PCM has gone into a “limp” mode, and is cutting power in second gear and above. We plan on simulating the solenoids and sensors with simple components. This should trick the PCM into thinking everything is OK and restore full power.
Paddle shifters and a ‘clutch’ switch are also possible. Time and money will determine if we get to this project.