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Automatic Transmission

Simply Complicated

Simply Complicated

Technically Speaking

Author: Wayne Colonna, Technical Editor

Technically Speaking

  • Author: Wayne Colonna, Technical Editor

The 3L30 (THM 180 C Trimatic) has a long history here in the United States, especially when Grumman Olson’s prototype of its Chevrolet U.S. Postal Service Long Life Vehicle (LLV) won the government’s durability contest. With an initial $1.1-billion contract in 1986, the facility in Montgomery, Pa., went on to produce more than 150,000 of these Postal Service vehicles using the 3L30 transmission until 1995.

Before that we saw it in the Holden from 1969 to 1975, the Chevette from 1977 to 1987, the Pontiac T 1000 from ’81 to ’87, the Rover Vitesse in ’83 and the 2300/2600 in 1984. Buick dealerships sold the Opel GT with the Trimatic transmission from 1969 to 1975. If we ran across a Fiat, we found this unit in the 124 from 1971 to ’74, the 131 from ’75 to ’81, and the Brava, Spider 2000 and Mirafiori during the same time frame as the 124 and 131. The 1981 Triumph Acclaim, the Peugeot 604 from ’77 to ’79 and the DeLorean from ’81 to ’82 are also on the list for using this little three-speed transmission.

Its reincarnation as a computer-controlled four-speed transmission is commonly known as the 4L30-E, but the original three-speed Trimatic design is familiar to us today, having been used in the 1.6-liter Geo Tracker from 1989 to 1997 and the 1989 to 1998 1.6-liter two-door Suzuki Sidekick.

It is in these two vehicles (Tracker and Sidekick) that we find a TCC system distinct from that used in any of the earlier TCC-equipped designs. Figures 1 and 2 show the internal adaptation and description of the components used to control converter-clutch apply. There we see that a TCC solenoid is fitted with some plumbing. The bottom pipe coming from the valve body is band-release pressure, otherwise known as 3rd-gear oil. This ensures that the vehicle will never have TCC until 3rd gear. When the solenoid is energized, this oil is routed through the upper pipe to the pump cover (see figures 3 and 4), where it strokes the converter-clutch control valve into a lockup position.

In addition to the solenoid receiving 3rd-gear oil, a governor-pressure switch time-controls (via speed) a voltage supply to the solenoid. In the example shown in figures 1 and 2, notice that the pressure switch is rated to close at 43.5 psi. Also notice that the solenoid is permanently grounded. Assuming a properly operating system, the transmission typically reaches 3rd gear by about 35 mph. This means the solenoid will have received 3rd-gear oil before governor pressure is high enough to close the switch (the idea is to prevent a converter-clutch apply on top of the 2-3 shift). Once governor pressure increases enough to close the switch (40 mph or above), voltage is supplied to the “already grounded” solenoid.

Once energized, the solenoid allows third-gear oil to pass through and stroke the converter-clutch control valve in the pump (see the partial hydraulic schematics in figures 5 and 6).

Figures 7 through 10 are typical wiring diagrams that reveal the external electronics controlling the voltage supply to the transmission.

Using a 1995 Suzuki Sidekick as an example, you can find the main relay under the dash (see Figure 11) and the transmission relay on the passenger side of the engine compartment forward of the battery (see Figure 12). These relay locations are similar to those in the Geo Tracker, as is the location of the ECM, under the dash up and to the left of the steering column.

Looking at the wiring diagrams, you can observe a number of points. Voltage supply to the transmission relay coil comes from the main relay. The ECM will ground the transmission relay after the transmission is at operating temperature and the vehicle is moving. With the transmission relay coil energized, power from the stop-lamp switch is supplied to the transmission through a white wire, energizing the solenoid after the governor-pressure switch closes. The wiring schematics note that the blue wire is not used with 1991 and later vehicles. 1989 and 1990 vehicles had this wire returning to the ECM as “governor-pressure-switch feedback,” informing the ECM whether the governor switch closed. A code 42 can occur in these vehicles if voltage on the blue wire to the ECM remains hot at all times, indicating a short to power. For 1991 and later, the wire remains in the harness but does not connect to the ECM (see Figure 13).

With this rather elaborate design for a simple converter-clutch-apply operation placed before you, it is easy to perceive the many causes of a loss of converter-clutch apply.

Mechanical causes could be a defective solenoid, a malfunctioning governor-pressure switch, the O-ring left off the pump end of the feed pipe, the bore plug that retains the converter-clutch control valve not sealing, the valve sticking or the converter failing.

Electronic causes include a bad splice in the voltage-feed circuit from the main relay to the transmission relay, a defective transmission relay, wiring problems from the relay to the ECM or from the relay to the transmission, internal transmission wiring problems, or a defective coolant-temperature sensor, stop-lamp switch, VSS or ECM. As I said, “Simply Complicated.”

The first step in diagnosing a complaint of no TCC apply is to check for any DTCs that may point you in an electrical direction. Another step would be to drive the vehicle at 45 mph and check for voltage to appear on the white wire. You easily could attach the meter to the white wire from under the hood, as there is a joint connector under the throttle body (see Figure 14). While the vehicle is being driven, voltage should become present. If you never see voltage, an external electrical problem exists (transmission relay, stop-lamp switch, wiring, ECM, ECT, VSS etc.). If you observe voltage, all the external electrical components are working.

Plug the connector back into the transmission and repeat the test, checking the blue wire for voltage. If you see voltage, there is an internal mechanical problem with the converter, the oil pipes or the solenoid (see figures 15 and 16 for solenoid bench-test procedures). If you do not see voltage on the blue wire, the governor-pressure switch is defective.

In 1995, GM issued a bulletin concerning a TCC chuggle/hunting condition that was caused by the governor-pressure switch opening and closing during vehicle speeds of 40-45 mph. The correction for this condition was production of a time-delay-module kit to be installed by the transmission relay under the hood. This module delayed the voltage supply to the transmission as an attempt to ensure that with increased vehicle speed, governor pressure also would increase past the threshold of the governor-pressure switch, eliminating the open/close toggle. The part number for this time-delay-module kit is 96041311.

The time-delay module has a red wire coming out of one terminal and an open terminal beside it. The white wire coming from the transmission relay is removed and connected to the open terminal on the time-delay module. The red wire is then placed into the transmission relay where the white wire previously was. This places the module in series between the relay and the transmission. The module is then clipped onto the nearby A/C-fan relay. For vehicles with A/C, the kit also includes a rubber holding fixture designed to slide onto a tab on the fuse box for attachment of the time-delay module.

Starting with late-production 1995 Trackers and Sidekicks, the governor-pressure switch was eliminated altogether, giving TCC control to the PCM.

Happy hunting – in-and-out TCC apply not intended.

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