278 Automatic Transmissions and Transaxles Copyright by Goodheart-Willcox Co., Inc. UD(1-2-3) OD(3-4) R(rev) V2 V1 V3 PT PT PT D2 D1 U1 UD AC AC H o t C o l d 2 5 S1 K2 L2 S2 O2 Manual valve V D 3 L N P R SW OD On Off 4 R O1 Figure 12-19. Solenoid-controlled check balls can be used to operate the clutch packs by controlling oil flow through the pas- sage. No valves are needed. (Chrysler) Line pressure Line pressure Manual valve Manual valve UD clutch UD clutch S3 S3 LR/CC solenoid de-energized LR/CC solenoid energized T/C & CC control valves T/C & CC control valves L/R clutch A B 2/4 clutch 2/4 clutch L/R clutch Off On L/R pressure switch L/R pressure switch Off On Sol Sw Valve Sol Sw Valve Figure 12-20. These illustrations show how the operation of a solenoid can be used to deliver oil pressure to one side of a valve. A—The pressure increase causes the valve to move. B—Removing the pressure allows pressure on the other side of the valve to return the valve to its original position. (Chrysler) Solenoid off Solenoid Check ball Feed (blocked) Solenoid on Feed Solenoid Check ball Output (to shift valves, etc.) Figure 12-21. These illustrations show a solenoid with an inter- nal check ball. Energizing the solenoid causes the check ball to either seal or open a passage in the solenoid assembly. (Ford) There are two ways to install solenoids so that they apply the needed clutches and bands: • Dedicated solenoids—each solenoid is dedicated to operating only its associated valve. There is one solenoid for each shift valve. In this arrangement, a four-speed transmission with three shift valves would have three shift solenoids. • Multi-shift solenoids—used in combination with pres- sure passages in the valve body. The pressure passages are arranged so that multi-shift solenoids affect some valves directly and others indirectly. In this arrange- ment, a four-speed transmission with three shift valves might have only two shift solenoids. Dedicated Solenoids On systems with a dedicated solenoid for each shift valve, each solenoid directly controls the operation of its related valve by removing or restoring pressure. Trace the oil circuit pathways in Figure 12-24 and you will notice that each solenoid controls the related shift valve by controlling the pressure delivered to that valve. Each of these solenoids sends pressure to the related valve to cause it to move. Other dedicated solenoids move the shift valve by exhausting (removing) pressure already Off On