A/T - 700R4 Oil Pressure Switch Locations
SIL 86-12 (June)SUBJECT:
The THM 700 R4 transmission has four (4) oil pressure switch locations in the control valve assembly (See Figure 1).
Oil pressure switches are activated by hydraulic pressure from the control valve assembly. Depending on design, a switch may function as the ground for an electrical circuit, or as a simple connecting switch. All switches are designed to be either normally open (N.O.) or normally closed (N.C.).
N.O. - means the switch will not allow electric current to flow until the switch is activated by hydraulic pressure.
N.C. - means the switch will allow electric current to flow until the switch is activated by hydraulic pressure
Also, the switches may be designed with either one or two terminals (see Figure 2). Single terminal switches are used to provide an electrical ground, while two terminal switches act as connecting switches.
SPECIFIC SWITCH FUNCTION
1. "Torque Converter Signal" switch (P/N 8642473). This is a single terminal normally open switch. The function of this switch is to make an electrical ground when the converter clutch is applied and break the ground when the clutch is released. For all 1982 and 1983 non-ECM vehicles with T.C.C. signal, this switch is wired in series with the third clutch switch (Figure 3).
2. Third Clutch Switch (P/N 8634333) . This is a two-terminal normally open switch. It is currently wired in series with the T.C.C. signal switch and allows current to flow to the T.C.C. signal switch only when the transmission is in third gear, although the high altitude option is the exception (see Figure 3)
3. 4-3 Downshift Switch (P/N 8642346). This is a normally closed two terminal switch. the 4-3 downshift switch is sometimes referred to as a pulse switch and performs the function of releasing the converter clutch when a 4-3 downshift is made (see Figure 4). The 4-3 downshift switch is activated by exhaust oil from the fourth clutch. After the fourth clutch oil has exhausted, the switch closes and allows the converter clutch to reapply. This momentary release (pulse) of the converter clutch allows the transmission to make a 4-3 downshift without any objectional shift feel.
4. Fourth Clutch Switch. One of three different switches may be installed in this location, depending on vehicle usage.
A. Fourth Clutch Switch (P/N 8634333)
This switch is a normally open two terminal switch. The function of this switch is to keep the converter clutch applied in fourth gear, regardless of engine vacuum (see Figure 5).
B. Fourth Discrete Switch (P/N 8634475 or P/N 8642569). These are normally closed single terminal switches. They are used in vehicles with ECM's. The purpose of either switch is to signal the ECM when the vehicle is in fourth gear (see Figure 6).
C. Fourth Clutch Switch P/N 8642473. This is a normally open single switch. The function of this switch is to keep the converter clutch applied in fourth gear regardless of any other controls (see Figure 7).
The illustrated procedure may be used in diagnosing the oil pressure switches.