Technically Speaking
- Author: Wayne Colonna, Technical Editor
SAAB/Volvo 50-42LE: No upshift from first gear
The past winter months brought to surface a condition of no upshift from first gear when cold with the SAAB/Volvo 50-42LE transmission. When it warms up, all shift sequences are restored. The time in which this occurs varies.
The problem has been traced to a mechanical failure of the No. 1 shift solenoid with the black connector (see Figure 1). Both the No. 1 and No. 2 shift solenoids are normally closed when off and open to exhaust when energized.
Figure 2 provides a first-gear hydraulic schematic. Shift solenoid 1 is off and shift solenoid 2 is on. With shift solenoid 1 off, pressure is allowed to stroke the 1-2 shift valve. When the 1-2 shift needs to occur, this solenoid is energized. The pressure from the solenoid stroking the 1-2 shift valve is exhausted and the valve closes by spring force. Line pressure then is directed into the B2 circuit (see Figure 3). And as previously stated, in cold-weather conditions, this solenoid does not open to exhaust when energized, preventing the upshift.
Since shift solenoid No. 2 has not exhibited this malfunction when cold, it is the only solenoid you can buy for both shift solenoids 1 and 2. Everything about the two solenoids is the same except for the direction of the connector, as you can see in Figure 4. There is enough length with the internal wiring harness to use a green-connector-style solenoid in the shift-solenoid 1 location, as you can see in figures 5 and 6.
The Volvo part number for this solenoid is 6843783.
On another note, each of the shift solenoids and the TCC solenoid have a basket-style filter (see Figure 7). The open top of the basket must face the spacer plate.
Installing these filters upside down will render the solenoids inoperative. The result of all three filters being upside down would be no TCC, no 1st, no 4th and no reverse. What a mess!
For those who are interested, ATSG now has a full-service Techtran Manual available for this unit that includes teardown and reassembly information with a complete set of hydraulics and a mapping of the valve body and case circuits.