TH700 Lockup Convertor in old Holden

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Page created by Qute July 16th 2006:

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Photo by AshWBTunna

TH700 Lock Up Converter:

TH700 Lock Up Converter Operation:

The Function of the Lock Up Converter is to reduce coupling losses once the Vehicle is up to Speed. A Lock Up Converter contains a Single Plate Clutch which is very like the Clucth Plate in a Manual Gearbox. When the Conditions are right Oil Pressure forces the Lock Up Clutch into activation.  Submitted by bf6379 on Mon, 17/07/2006 - 20:19.

Here is a copy of some posts I made on this subject a while back:

The four pin connector (only has three pins fitted) has two pins for the lock up torque converter, one has +12 volts supplied to it when the ignition is on. The other is grounded by the ECM to lock the torque converter.

The third pin is for the transmission 4th gear / overtemperature signal. If the transmission is in 4th gear and over a certain temperature (very hot) this pin will be connected to ground.
Photo by AshWBTunna

If you are not using an ECM, you can drop the pan off the transmission and bypass the temperature switch. This pin will then be grounded when the transmission is in 4th gear and can be used to control the torque converter clutch via a switch in the cabin.

I have heard of other setups that use micro-switches on the accelerator and wired into the brake light switch also. It is not desirable to have the torque converter locked under closed throttle, more than about 60 percent throttle or when braking. It should also only be locked above certain road speeds, this is why using the 4th gear switch is a convenient solution. The hydraulic system in the transmission makes it impossible for the torque converter to lock in 1st gear. Locking the torque converter reduces engine RPM, improves economy and reduces heat in the transmission.
Photo by AshWBTunna

You will have to hook up the TV cable, it is not only used for kickdown it also controls the shift points just like the vacuum operated modulator valve on the trimatic.

You can use a toggle switch to switch the Torque Converter Clutch (TCC) on and off, but you will have to use it with some level of discretion. If you leave it turned on the TCC will lock whenever the transmission is in 2nd, 3rd or 4th gear. Locking the TCC at low RPM and low speed almost stalls the engine. You really only want it locked once you are cruising above about 80 km/hr. Downshifts are also very rough if you don't unlock it before you give it a bootfull.

You could hook a light up to the 4th gear/overtemp pin, but I wouldn't bother, It will probably only come on on a hot day if you are towing a caravan. Locking the TCC whenever possible means the transmission won't get hot anyway.
Photo by AshWBTunna

The connector on the transmission has three pins (four holes but only three pins) The TCC pins are the ones towards the outside of the transmission. The front one (pin A) is +12 volts and the rear one (pin D) is chassis ground. You can either supply 12 volts to pin A and switch the ground to pin D or ground pin D (connect to a bolt on the body of the car somewhere) and then take +12 volts (only with ignition on) via a switch to pin A. It only draws about half an Amp.

The 4th gear/overtemp signal (pin B) is the front pin toward the centre of the transmission. This gets connected to ground inside the transmission when transmission fluid temp gets over 130 deg C in 4th gear.

The VN/VP ECMs control the TCC, it will lock under the following conditions:
Vehicle speed above 72 km/hr.
Engine temp above 44 deg C.
Throttle position above 4 percent and below about 50 percent (varies with vehicle speed).
Photo by bf6379.

If the TV cable is adjusted correctly, the TCC will unlock at a throttle position of about 10 percent less than the kickdown point. With a TH700 kickdown is determined by vehicle speed and throttle position, not only at full throttle like the electric kickdown trimatic.
If the ECM receives the 4th gear/overtemp signal, The speed input and engine temperature are disregarded. The TCC will lock once 4th gear is engaged, whenever the throttle is above 4 percent open. This reduces the amount of heat produced in the transmission, to allow it to cool down. It will not unlock before a 4th to 3rd kickdown.





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