Torque converter lock up control 700R4

by: Cobalt327, Crosley
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Converter lock up wiring

This requires a simple 12 volt circuit. 12 volts to the solenoid and a ground to complete the circuit. When the brakes are applied the relay switches to pin 87 and the circuit is broken, thus unlocking the torque converter. A common Bosch-type relay used.

If you do not understand basic wiring, get help from someone who does or research it first. It's not rocket science. The Relay Applications Guide under 'Resources' below has the required info, for example.

Basic wiring diagram

Pressure switches

Notice these pressure switches are silver in color. This means they are NO = Normally Open. When pressure is applied, the switch closes the internal contacts to complete the circuit. Both of these pressure switches are "on/off" design. Pressure turns them "on", no pressure they are "off".

The pressure switch with 1 pole is self-grounding. This means a wire connected to it will be grounded through the switch case when pressure is applied to the switch. The 2 post switch can pass current through the switch when pressure is applied. No voltage passes through the switch when there is no pressure.

These switches are not designed for use on the outside of the transmission case because they are made with bleed holes in them to equalize the pressure from the heat of the ATF they are exposed to. For use on the outside of the transmission, use switches rated for external use to avoid possible fluid leakage.

Pressure switch with one post is self-grounding. This means a wire connected to it will be grounded through the switch case when pressure is applied to the switch.

When pressure is applied, the two post switch will allow current to pass through it to a single wire lock up solenoid.

Lock up solenoids

Types of lock up solenoids

• 1 wire solenoid, early design
• More common 2-wire solenoid, late design

Solenoid on the left with 1 red wire is a self-grounding lock up solenoid. The 2-wire solenoid has a red wire for 12 volts and a black wire for ground.

Valve body location for switch

Location circled on a 700R4 valve body has pressure when the transmission is in fourth gear to allow only fourth gear lockup of the torque converter clutch (TCC).

Resources

• TCC wiring
• TH700R4/4L60 swap info]
• Relay Applications Guide