APPLICATION
An identification tag is attached to the rear case half. (Scheme 1) The tag provides the transfer case model number, low range reduction ratio and assembly part number.
Transfer Case Identification. Scheme 1
DESCRIPTION
The transfer case is used to provide power flow to the front axle. The transfer case also provides a means of disconnecting the front axle, allowing better fuel economy and quieter operation when the vehicle is driven on improved roads where four-wheel drive is not required. In addition, the transfer case provides an additional gear reduction when placed in low range, which is useful when difficult off-road conditions are encountered.
A New Process Model 231 transfer case is used on all vehicles covered in this article. The Model 231 is an aluminum cased, chain-driven unit with 4 modes of operation: neutral, 2-wheel drive high range, 4-wheel drive high range, and 4-wheel drive low range. Gear reduction for low range is provided by a planetary gear set.
A floor-mounted shift lever is used to select the desired operating range. Refer to TRANSFER CASE SHIFTING PROCEDURE TABLE (4WD) and Fig. (Scheme 2). Indicator lights on the floor console show the current mode of operation. When 4-wheel drive has been selected, the 4-wheel drive indicator light will come on when the front axle has engaged. A slight delay for the front axle indicator light to come on is normal.
Shift Pattern & Procedure. Scheme 2
| SHIFTING FROM | SHIFTING TO | PROCEDURE |
|---|---|---|
| "2 WHEEL" (2WD) (Rear Wheel Drive) | "4 HIGH" (4WD). Used for low-traction road surfaces only. (Do Not use on dry pavement). | 1. (1) May be made when vehicle is moving. 2. Move transfer case shift lever into position. 3. Front axle locks automatically. |
| "2 WHEEL" or "4 HIGH" (High Range) (Do Not use on dry pavement). | "4 LOW" (Low Range). Used on low-traction road surface only. (Do Not use on dry pavement). | 1. Stop vehicle, place trans. in "N". 2. Press shift lever button, move transfer case shift lever in 1 continuous motion. Do not pause in Neutral. This could result in gear clash. 3. Axle locks automatically |
| "4 LOW" (Low Range) (Do not use on dry pavement). | "2 WHEEL" or "4 HIGH" (High Range) Use 4 High on low- tractiopn surfaces only. (Do Not use on dry pavement). | 1. Stop vehicle, place trans. in "N". 2. Press shift lever button, move transfer case shift lever in 1 continuous motion. Do not pause in Neutral. This could result in gear clash. it may be necessary to reduce speed or stop vehicle. |
| "4 HIGH" (Four Wheel Drive) (Do not use on dry pavement). | "2 WHEEL" (Rear Wheel Drive) shifting from "2 WHEEL" to "4 HIGH" while vehicle is moving | 1. May be made while vehicle is moving. 2. Move transfer case shift lever into position. |
| (1) In extreme cold weather, if difficulty is encountered in shift from 2-WHEEL to 4HI while vehicle is moving, it may be necessary to reduce speed of stop vehicle. | ||
| (1) | In extreme cold weather, if difficulty is encountered in shift from 2-WHEEL to 4HI while vehicle is moving, it may be necessary to reduce speed of stop vehicle. |
TRANSFER CASE SHIFTING PROCEDURE
NORMAL OPERATION (2WD)
When the transfer case is in "2 WHEEL" range, torque flows from the input gear to the range shift hub and mainshaft, through the drive shaft, to the rear axle. A switch in the shifter mechanism causes the "2 WHEEL" indicator light to turn on.
HIGH RANGE OPERATION (4WD)
Shifting into "4 HIGH" range causes the following to happen
- A switch in the shifter mechanism causes the "2 WHEEL" indicator light to turn off and the "4 HIGH" indicator light to turn on. The front axle indicator light does not come on immediately.
- Torque flows from the input gear to the mainshaft the same as in "2 WHEEL" position. The shift linkage moves the mode synchronizer sleeve into engagement with the clutch teeth of the drive sprocket. This locks the drive sprocket to the mainshaft through the synchronizer sleeve.
- Torque is transmitted through the drive sprocket and drive chain to the driven sprocket and output shaft. Torque then flows through the front drive shaft to the front axle.
- The shift mechanism in the transfer case triggers a vacuum switch. (Scheme 3) Engine vacuum is then applied to a vacuum actuator, mounted on the right fender well, after a delay of about three seconds. The delay is provided by a restrictor orifice. The delay allows the system to synchronize properly.
- The vacuum actuator pulls a cable, which pulls the shift fork in the front axle. This connects the right axle output shaft to the front axle differential. Torque now is available at the front wheels.
- The front axle shift mechanism, when fully engaged, closes a switch, causing the front axle indicator light to come on. For more information on the front axle shift mechanism and vacuum actuator, see appropriate DRIVE AXLE - FRONT article in the DRIVE AXLES section.
- If the shift lever is moved back to "2 WHEEL" position, the operation in the preceding steps is reversed. In addition, when the transfer case switch turns the vacuum to the vacuum actuator off, it connects the vacuum actuator hose to atmosphere through a vent hose. The actuator can then return to the two-wheel drive position.
Vacuum Actuator System. Scheme 3
LOW RANGE OPERATION (4WD)
- When the transfer case is shifted into "4 LOW" position, torque flow and operation are similar to "4 HIGH" range, except that the range shift hub engages the planetary carrier. The planetary gear set then provides a gear reduction of 2.72:1 to both the front and rear axles.
- A switch in the shifter mechanism causes the "4 HIGH" indicator light to turn off and the "4 LOW" indicator light to turn on.
SERVICING
Note. Refer to the TRANSFER CASE - OVERHAUL (207/231) article.
FOUR WHEEL DRIVE DOES NOT ENGAGE
| POSSIBLE CAUSE | CORRECTION |
|---|---|
| Vacuum hoses kinked, disconnected, or broken. | Check routing of hoses. Repair or replace as needed. |
| Engine vacuum insufficient to activate vacuum actuator. At least 12 In. Hg. (-40 kPa) of vacuum is required at the actuator. | Repair or tune engine as required. |
| Actuator cable kinked, misrouted, or disconnected. | Repair or replace as needed. |
| Faulty vacuum actuator. Check for holes in diaphragm or other damage. | Replace if necessary. |
| Faulty vacuum switch. | Replace. |
| Faulty 4WD indicator light, sw., or wiring (4WD engaging but indicator light not coming on). | Repair as needed. |
| Transfer case linkage improperly adjusted or disconnected. | Adjust or repair. |
| Faulty transfer case: Drive chain broken, range selector ring broken, etc. | Repair. |
| Faulty front axle. | See DRIVE AXLE - FRONT in DRIVE AXLE section. |
FOUR WHEEL DRIVE DOES NOT ENGAGE
FOUR WHEEL DRIVE WILL NOT DISENGAGE
| POSSIBLE CAUSE | CORRECTION |
|---|---|
| Faulty wiring or front axle sw. (4WD disengaging but indicator light staying on). | Replace or repair wiring. |
| Transfer case vacuum sw. vent hose or vacuum actuator hose kinked or plugged. | Replace or repair. |
| Transfer case vent filter plugged. | Replace or repair. |
| Actuator cable kinked or damaged. | Replace. |
| Faulty transfer case vacuum sw. | Replace. |
| Transfer case linkage binding or improperly adjusted. | Transfer case linkage binding or improperly adjusted. |
| Faulty front axle shift mechanism. | Repair. |
FOUR WHEEL DRIVE WILL NOT DISENGAGE
DRIVE FOUR WHEEL DISENGAGES UNDER LOAD
| POSSIBLE CAUSE | CORRECTION |
|---|---|
| Insufficient vacuum at vacuum actuator due to vacuum leak, poorly tuned engine, or kinked vacuum hose. 12 in.hg. (-40 kPa) of vacuum is required at the actuator for proper operation. | Tune engine or repair vacuum hoses |
| Vacuum system not venting properly due to kinked hose, plugged vent, or faulty transfer case vacuum sw. | Repair. |
| Faulty transfer case or front axle shift mechanism. or improperly adjusted. | Repair. |
DRIVE FOUR WHEEL DISENGAGES UNDER LOAD
TRANSFER CASE SHIFT LEVER DIFFICULT TO SHIFT OR WILL NOT
SHIFT INTO 4 LOW OR NEUTRAL (VEHICLE MOVING)
| POSSIBLE CAUSE | CORRECTION |
|---|---|
| Vehicle in motion when attempting to shift. Stop vehicle when shifting into or out of 4L or N. | None required. |
TRANSFER CASE SHIFT LEVER DIFFICULT TO SHIFT OR WILL NOT SHIFT
TRANSFER CASE DIFFICULT TO SHIFT
| POSSIBLE CAUSE | CORRECTION |
|---|---|
| In extremely cold weather, it may be necessary to reduce speed or stop before shifting from 2 Wheel to 4 High. Indicator light not coming on. | None is required. |
| If vehicle has been operated for an extended period in 4 High mode on dry pavement, difficult shifting may result due to driveline torque load. Stop vehicle, shift trans. into neutral and shift transfer case into desired mode. | Operate vehicle in 2 WHEEL mode on dry pavement. |
| Transfer case linkage binding. | Adjust or Repair |
| Low transfer case lubricant level or improper lubricant used. | Fill with proper lubricant. |
| Internal transfer case problem. | Repair. |
TRANSFER CASE DIFFICULT TO SHIFT
TRANSFER CASE NOISY IN ALL MODES
| POSSIBLE CAUSE | CORRECTION |
|---|---|
| Low lubricant level, or improper lubricant used. | Fill with proper lubricant. |
| Internal transfer case problem. | Repair. |
TRANSFER CASE NOISY IN ALL MODES
NOISY IN OR JUMPS OUT OF 4 LOW RANGE
| POSSIBLE CAUSE | CORRECTION |
|---|---|
| Transfer case not completely engaged in 4 LOW range. Stop vehicle, shift into NEUTRAL, then back to 4 LOW. | None required. |
| Shift linkage loose or binding. | Repair. |
| Transfer case internal shift mechanism faulty. | Repair. |
NOISY IN OR JUMPS OUT OF 4 LOW RANGE
LUBRICANT LEAKING FROM TRANSFER CASE VENT
| POSSIBLE CAUSE | CORRECTION |
|---|---|
| Transfer case overfilled. | Drain to proper level. |
LUBRICANT LEAKING FROM TRANSFER CASE VENT
LUBRICANT LEAK AT OUTPUT SHAFT SEALS
| POSSIBLE CAUSE | CORRECTION |
|---|---|
| Transfer case overfilled. | Drain to proper level. |
| Vent hose plugged or kinked. | Repair. |
| Output shaft seals damaged or incorrectly installed. | Replace. |
LUBRICANT LEAK AT OUTPUT SHAFT SEALS
ABNORMAL FRONT TIRE WEAR
| POSSIBLE CAUSE | CORRECTION |
|---|---|
| Front end needs alignment. | Align to specification. |
| Extended operation on hard, dry surfaces in 4 HIGH mode. | Operate vehicle in 2 WHEEL mode on hard, dry surface. |
ABNORMAL FRONT TIRE WEAR
| Symptom | For Diagnosis |
|---|---|
| One or more Indicator Assembly Lamps do not Function. | Do TEST A . and TEST B . |
| Indicator Assembly Front and Rear Axle Display does not function. | Do TEST C . check WHT (150) wire, WHT (156) wire, and BLK (150) Wire for an open |
| No Indicator Assembly Lamps function. | Do TEST A . Check BRN/WHT (141) wire and BLK (150) wire for an open |
INDICATOR ASSEMBLY LAMP INDICATION-TO-DIAGNOSTIC TEST MENU
TEST A - SELECTOR QUADRANT SWITCH TEST
Measure Continuity at Selector Quadrant Switch with switch disconnected. If continuity does not exist at any or all terminals replace the Selector Quadrant Switch. If continuity does exist, refer to the Symptom Table.
TEST B - INDICATOR ASSEMBLY TEST
Check for voltage at Indicator Assembly while connected with Selector Quadrant Switch Disconnected. Measure Voltage From (C2) 1-5 and (C1) 1 & 5 to Ground. See WIRING DIAGRAMS . If test lamp does not lights replace Indicator Assembly.
TEST C - FRONT AXLE SWITCH TEST
Check for voltage at C190 with Front Axle Switch connected and Selector Quadrant in detent position 2 or 4. Measure from A and B to Ground, if tests lamps lights refer to the Symptom Table. If test lamp does not light, Check WHT(150) wire or WHT(156) wire for a open. See WIRING DIAGRAMS . If an open was found, replace front axle switch.
REMOVAL & INSTALLATION
Note. Refer to the TRANSFER CASE - OVERHAUL (207/231) article.
OVERHAUL
Note. Refer to the TRANSFER CASE - OVERHAUL (207/231) article.
TORQUE SPECIFICATION
Note. Refer to the TRANSFER CASE - OVERHAUL (207/231) article.
