Torque Converter Lockup

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Torque converter cut away

Introduction
This mod only applies to cars with automatic transmissions.


The torque converter can provide extra torque and allows the engine and drive shaft to rotate at different speeds. In performing this function the torque converter wastes energy and generates heat. Most if not all torque converters have a lock up ability where the engine shaft and drive shaft can be locked together by way of a friction disc on the outside rim of the torque converter. When they are locked together the transmission acts like a manual transmission and therefore wastes very little energy. The lock up function is often performed by an electrically controlled solenoid which operates a valve allowing transmission fluid to push the TC against the transmission housing.


The ECU will often lock up the torque converter when the car reaches a particular speed and gear but usually only under low load conditions. Ecomodders may prefer to lock up their torque converter at lower speeds and lower gears for better efficiency or to keep locked up while climbing hills or accelerating. In addition to reducing heat losses through the TC, this allows one to keep the engine in a more efficient load/rpm range.


Contents

Instructions for mod

Method for testing when torque converter is engaged
To find out if your torque converter is locking up at any time, when the engine is in gear press the gas pedal down.

If the torque converter is not locked to the drive shaft the RPMs will rise quickly.

If the torque converter is locked the RPM's will stay constant until the speed changes no matter how much power you give to the engine.

Identifying torque converter lock up signal
Consult a wiring diagram or workshop manual.

Many work shop manuals and wiring diagrams will not have detail about the connections to the automatic transmission. When the torque converter signal wire can't be found from documentation, perform the following steps to locate the signal wire

Diagnostic LED

- Locate the automatic transmission
- Identify all control wires that are connected to the transmission
- Cut the insulation away from the wire
- Solder a wire to the exposed wire. Ensure the wire is long enough to extend into the cabin of the car
- Solder a LED and resistor in series to the wire in the cabin. Connect the other side of the resistor plus LED to 0v which is the most exposed metal in the cabin
- Take the car for a drive. If the correct signal wire has been soldered to the LED, it will light up or turn off when the torque converter is engaged.
- If the LED state does not correspond to the torque converter action, locate another signal wire on the transmission and repeat the process.

Performing the modification

Torque converter switch

- Once the torque converter signal has been isolated trace it back to the closest location to the cabin which is likely at the ECU.
- Cut the signal wire and solder wires of the suitable gauge (thickness) and length to reach the desired mounting location.
- Using a single pole double throw switch (2 position switch) connect the common terminal to the transmission side of the signal wire. Connect the other end of the signal wire (the ECU side) to one of the other switch terminals. Connect a 12v signal or 0v to the other terminal of the switch (12v if the LED turned on when TC locked or 0v if LED turned off when TC locked).

This arrangement will allow the driver to select between the ECU controlled torque converter signal and a locked up setting.

User experiences

Please enter your user name and any relevant data in the table

User data
User Name Car Make, Model, Year Cost of Mod Time to Perform Mod MPG Before Mod MPG After Mod MPG improvement guess Instruction Link
Saand Mazda, 626, 91 $2 2 Hours 12% improvement between locked and unlocked torque converter. Not an accurate test
RH77 '98 Acura Integra $1-2 1-2 Hours Unk. Unk. ~10% Estimate. Testing not conducted due to variable environment between tanks. Immediate FE feedback device (SGII) demonstrates the estimated improvement.
Oil pan 4 1984 chevy suburban N/A N/A 21mpg 16mpg This is the 24% decrease in fuel economy observed when my torque converter lockup quit

Problems / Consequences of mod

- Possible Jerky shift changes
- Possible damage to the torque converter if a shift change occurs under a high load
- Low engine RPMs when the torque converter lock is engaged in some lower gears as most cars usually won't engage the torque converter lock in low gears

References

Forum thread links

Freezing the Slushbox. Torque Converter on-demand lockup switch.

External links

The Free Mod Series: Part VIII Electronic Transmission Controller - Toyota Forums :: Toyota Nation

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