Issue Summary:
- In a Nissan RE4FO4A or Villager 4F20E, slipping or no second gear may be caused by insufficient spring tension on the 1-2 accumulator piston or a stuck 1-2 accumulator regulator valve.
- We have in-depth information on retrieval of diagnostic trouble codes for Nissan vehicles.
- Harsh upshifts on electronically controlled Nissan transmissions may be caused by a faulty dropping resistor or a poor connection at the resistor.
- In Toyota Previas with four-cylinder engines and A46DE transmissions, stacked shifts or no passing gear may be caused by a broken wiring harness or faulty throttle-position sensor.
- GM introduced a new-design overrun roller clutch into the THM 4L80-E as a running change beginning in March 2001. We cover the parts affected by this engineering change.
Before and/or after rebuild, the vehicle exhibits either no upshift into second gear or slipping in 2nd gear.
Cause No. 1:
One cause may be either insufficient spring tension on the 1-2 accumulator piston or a stuck 1-2 accumulator regulator valve resulting in restriction of 2nd apply oil. Refer to Figure 1 for a description of the 1-2 hydraulic circuit with either a stuck valve or insufficient spring tension on the 1-2 accumulator piston.
See Figure 2 for a description of the 1-2 hydraulic circuit with sufficient spring tension on the 1-2 accumulator piston.
Cause No. 2:
Another cause may be that the 2/4 servo return spring has been switched with the N/D accumulator spring. If the N/D accumulator spring is installed in the location for the 2/4 servo return spring, it will coil-bind before the 2/4 servo gets a chance to apply the band fully, resulting in no second gear. See Figure 3 for spring specifications and proper placement of the 2-4 servo return spring and the N-D accumulator spring.
Correction No. 1:
Insert a pressure-regulator-valve spring from a 700-R4 inside the original 1-2 accumulator spring as shown in Figure 4. Install a spring with 1.5-2.0 pounds more tension in the pilot-valve line-up, as shown in Figure 4.
Also install two 125C front-planetary shims on the pressure-regulator valve to increase line pressure, as shown in Figure 5. This will greatly increase transmission durability and reliability.
Correction No. 2:
See Figure 3 for spring specifications and place the 2-4 servo return spring and the N/D accumulator spring in their proper locations.
Before or after overhaul, some Nissan vehicles with electronically controlled transmissions may exhibit harsh upshifts before or after overhaul.
The cause may be a faulty dropping resistor or a poor connection at the dropping resistor.
Refer to Figure 6 for the location of the dropping resistor.
See Figure 7 for the procedure to measure resistance.
See Figure 8 for the voltage-check procedure for the dropping resistor. Repair the connection and/or replace the dropping resistor as needed.
Toyota Previas equipped with 4-cylinder engines and A46DE transmissions may exhibit stacked shifts and/or no passing gear.
The cause may be a broken wiring harness at the throttle-position-sensor (TPS) connector, a break in the harness from the TPS where it enters a protective cover (see Figure 9) or a faulty TPS.
See Figure 10 to test the TPS diagnostic-voltage output at the diagnostic connector.
Locate the break in the harness (refer to Figure 9). If the wires are broken where the harness enters the protective cover, add some new wire to the harness and reconnect the harness. If the wires are broken at the connector, where they cannot be repaired, replace the connector with either a TPS connector that has 7 or 8 inches of the harness from a 1.8-liter Tercel engine from a salvage yard or a new upper wire harness for the whole upper engine from Toyota. If the wire harness is good, test the TPS as shown in Figure 11 and replace it if necessary.
Beginning in March 2001, GM introduced a new-design overrun roller clutch into the THM 4L80-E as a running change. This engineering change affected many other related parts.
Increased durability and reliability with the new-design roller clutch by reducing the ability of the rollers to skew.
(1) Overrun Roller Clutch – Entirely new design with smaller-diameter rollers, and the rollers now are trapped inside a “shoe” to help prevent skewing. The springs put pressure on the shoe (see Figure 12).
(2) Overrun-Clutch Housing – Requires a different ramp angle on the inner cam to accommodate the new-design roller clutch, as shown in Figure 12. The snap ring also was moved away from the back of the roller clutch; this required a new snap-ring groove that is lower in the housing, as shown in Figure 13.
(3) Overrun Roller Clutch Return Spring – Now requires a recess in the return-spring retainer to accommodate the relocated snap-ring groove, as shown in Figure 13.
(4) Retainer Snap Ring – New design has revised dimensions, as shown in Figure 13. The new-design snap ring is thinner and narrower.
(5) Overdrive Planetary Carrier – The new design incorporates a smaller-diameter roller-clutch outer race into the overdrive carrier, as shown in Figure 14.
None of the current-design parts listed will inter-change with the previous-design-level parts. They will retrofit all models when used as a service package.
- Overrun Roller Clutch Service Package (New Design) ..24222160
- Turbine-Shaft Assembly (2nd Design) ……………………….24200128
Special Note:
- If installing this service package into an early model with the first-design turbine shaft, you also must buy the second-design turbine shaft (see Figure 15). The changes included shot-peening the area around the forward-clutch feed hole, which is a smaller diameter and is drilled through the turbine shaft (See Figure 15).
December 2001 Issue
Volume 18, No. 12
- Nissan RE4FO4A or Villager 4F20E: Slipping or No 2nd Gear
- Nissan Electronically Controlled Transmissions: Harsh Upshifts
- Toyota Previa A46DE: Stacked Shifts/No Passing Gear
- THM 4L80-E/4L80-EHD: New-Design Overrun Roller Clutch