1997 Chevrolet S10 Pickup

1997 TRANSFER CASES General Motors Corp. New Venture 231 Overhaul

1997 TRANSFER CASES

General Motors Corp. New Venture 231 Overhaul

IDENTIFICATION
Transfer case can be identified by an I.D. tag, located on rear case. I.D. tag provides model number, serial
number and low range ratio. Date of manufacture is the serial number (I.D. number). This information is
necessary when ordering parts.

DESCRIPTION
Model 231 transfer case is a part time, chain-driven, 4-position unit with 2-piece aluminum case. Torque input
in 4WD high and low range is undifferentiated. 2WD operation is achieved by a vacuum shift motor. Shift
motor disconnects right front axle when 2WD is selected. Vacuum shift motor is controlled by a vacuum switch
located on front of transfer case and actuated by shift sector.

ON-VEHICLE SERVICE
FRONT OIL SEAL

Removal & Installation

1. Mark front drive shaft and flange for installation alignment reference. Remove front drive shaft. Remove
flange. Discard washer and nut. Using a screwdriver, carefully remove oil seal. Ensure seal contact
surface is clean.
2. Apply ATF to seal lip and flange seal surface. Install NEW oil seal. Install flange and NEW washer and
nut. Tighten nut to specifications. See TORQUE SPECIFICATIONS . Install front drive shaft using
alignment marks. Check transfer case fluid.

EXTENSION HOUSING OIL SEAL & BUSHING

Removal & Installation

1. Mark rear drive shaft and flange for installation alignment reference. Remove rear drive shaft. Tap
extension housing in a clockwise direction and remove extension housing. DO NOT pry on extension
housing. Using a screwdriver, remove oil seal from extension housing.
2. Using bushing driver, replace bushing in extension housing. Install NEW extension housing oil seal.
Apply silicone sealant to extension housing mating surface. Install extension housing. To complete
installation, reverse removal procedure.

ADJUSTMENTS
GEARSHIFT LINKAGE

Remove transfer case shift lever knob retainer. Remove shift lever knob. Remove floor console. Place shift
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 1997 Chevrolet S10 Pickup
1997 TRANSFER CASES General Motors Corp. New Venture 231 Overhaul

lever in Neutral. Pry control cable end from shift lever. Loosen control cable lock nut. Check transfer case to
ensure it is in Neutral. Ensure shift lever is in Neutral. Turn shift lever end of cable in or out as needed until it is
aligned with shift lever. Install control cable on shift lever. Tighten control cable lock nut.

TROUBLE SHOOTING
SYMPTOM DIAGNOSIS

Will Not Shift Or Difficult To Shift Into Gear

Vehicle speed too high; slow vehicle to 2-3 MPH to shift. Vehicle operated too long on dry paved surface; stop
vehicle and place in Reverse or Neutral to relieve driveline torque. Ensure transfer case external linkage is not
binding. Ensure correct fluid is used. Internal parts may be worn or damaged.

Noisy In All Gears

Check fluid level. Ensure correct fluid is used. If fluid is okay, locate possible internal mechanical problem.

Jumps Out Of Gear Or Noisy In 4WD

Transfer case not completely in gear; check shift linkage. Range fork damaged. Shift fork pads are worn or shift
fork binding. Low range gear worn.

Fluid Leaking From Vent Or Seals

Transfer case overfilled. Vent plugged. Output shaft seals are damaged or not installed properly.

TESTING
VACUUM SWITCH

Shift to 2WD position. Locate vacuum switch on front of transfer case. Apply 15 in. Hg vacuum to "L". See
Fig. 1 . Vacuum should be present at "M". Connect a vacuum gauge to "N". Shift to 4WD position. Apply
vacuum to "L". Vacuum should be present at "N". If switch fails any test, replace switch.

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 1997 Chevrolet S10 Pickup
1997 TRANSFER CASES General Motors Corp. New Venture 231 Overhaul

Fig. 1: Testing Vacuum Switch

Courtesy of CHRYSLER CORP.

REMOVAL & INSTALLATION

TRANSFER CASE

Removal

1. Shift transfer case into 4H position. Disconnect negative battery cable. Raise and support vehicle. Drain
fluid.
2. Mark front and rear output shaft yokes and drive shafts for reassembly reference. Support transfer case
with hydraulic jack and remove rear crossmember and skid plate, if equipped. Remove front and rear
drive shafts.
3. Disconnect transfer case gearshift linkage, vent hose and all electrical and vacuum connections. Remove
transfer case-to-transmission bolts. Remove transfer case from vehicle.

Installation

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 1997 Chevrolet S10 Pickup
1997 TRANSFER CASES General Motors Corp. New Venture 231 Overhaul

1. Clean all old gasket material from transmission and transfer case mating surfaces. Position NEW gasket
on transfer case with orientation tab at upper left bolt hole.
2. Install transfer case, aligning splines of input shaft with transmission. Slide transfer case forward until
seated against transmission. Install transfer case-to-transmission bolts and tighten to specification. See
TORQUE SPECIFICATIONS . Install rear crossmember and skid plate.
3. Reconnect gearshift linkage, vent hose and all electrical and vacuum connections. Using reference marks
made during removal, reinstall front and rear drive shafts. Refill transfer case. Adjust gearshift linkage.
See ADJUSTMENTS . To complete installation, reverse removal procedure.

TRANSFER CASE DISASSEMBLY

1. Remove front companion yoke. See Fig. 2 . Discard washer and nut. Shift transfer case to 4L and remove
extension housing. Remove rear bearing snap ring. Using 2 screwdrivers under each tab, remove retainer
housing. Remove rear case and oil pump as an assembly.
2. Remove oil pump pick-up screen and tube from rear case. Remove oil pump. Remove "O" ring from oil
pump and discard. Do not separate oil pump halves. Pump must be replaced as an assembly if necessary.
3. Remove mode spring. Using a soft hammer, tap front output shaft upward and remove with drive chain as
an assembly. Remove mainshaft, mode fork and shift rail as an assembly. Remove mode fork and shift
rail from synchronizer sleeve.
4. Mark synchronizer sleeve position for reassembly reference. Remove synchronizer sleeve from
mainshaft. Remove synchronizer hub snap ring. Remove synchronizer hub, stop ring and drive sprocket.
Slide range fork pin out of sector.
5. Remove range fork and shift hub as an assembly. Remove range lever from sector shaft. Remove shift
sector, bushing and "O" ring. Remove shift detent pin, spring and plug. Remove front bearing retainer.
Remove input gear snap ring.
6. Press input and low range gear assembly from input gear bearing. Remove low range gear snap ring.
Remove input gear retainer, thrust washers and input gear from low range gear.
7. Remove all oil seals. Remove magnet from front case. Remove front bearing snap ring. Using a plastic
hammer, remove front bearing. Press input gear bearing from front case.
8. Using slide hammer and internal puller, remove input gear pilot bearing. Press bearings from drive
sprocket. Using internal puller and slide hammer, remove output shaft rear bearing.

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 1997 Chevrolet S10 Pickup
1997 TRANSFER CASES General Motors Corp. New Venture 231 Overhaul

Fig. 2: Exploded View Of Model 231 Transfer Case

Courtesy of CHRYSLER CORP.

CLEANING & INSPECTION

Clean all parts with solvent. Dry with compressed air. Replace all oil seals, "O" rings and snap rings. Check all
parts for wear or damage. Replace all worn or damaged parts. If low range annulus gear inside front case is
damaged or worn, front case and gear must be replaced as an assembly. Replace oil pump as an assembly if any
part is damaged or worn.

TRANSFER CASE REASSEMBLY

NOTE: When installing bearings, ensure bearing bores are aligned with oil feed holes.

1. Lubricate all parts with Dexron III before installing. Install output shaft front bearing with NEW snap
ring. Install output shaft oil seal in front case. Install snap ring on NEW input gear bearing. See Fig. 2 .
2. Press input gear bearing so snap ring is seated against case. Using press, install NEW input gear pilot
bearing. Assemble low range gear, input gear, thrust washers and retainer.
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 1997 Chevrolet S10 Pickup
1997 TRANSFER CASES General Motors Corp. New Venture 231 Overhaul

3. Install snap ring. Ensure snap ring is seated in low range gear groove. Start input gear shaft into bearing
in front case. Press input shaft gear into bearing.

CAUTION: DO NOT press against end surfaces of gear. Failure to use proper
size tool could lead to gear case or thrust washer damage.

4. Install input gear snap ring. Install oil seal in front bearing retainer. Apply a 1/8" bead of silicone sealant
to retainer mating surface. Align oil channel in retainer with oil feed hole in case. Install retainer on case.
Tighten bolts to specification.
5. Install sector shaft "O" ring and bushing. Install range sector in case. Install range lever and nut. Install
detent, detent spring and plug. Tighten to specification. See TORQUE SPECIFICATIONS . Install
NEW pads and fork rail bushings on range fork. Install range fork and shift hub.
6. Ensure range fork pin is engaged with range sector slot. Press front bearing in drive sprocket until bearing
is flush with bore edge. Install rear bearing until bearing is flush with lower edge of chamfer in bearing
bore.
7. Install inserts and spring in synchronizer hub. Install sprocket on mainshaft. Install synchronizer stop ring
on mainshaft. Ensure stop ring is seated. Install synchronizer hub on mainshaft. Align and seat hub inserts
on stop ring lugs. Install synchronizer hub snap ring.
8. Install synchronizer sleeve on hub. Ensure sleeve is positioned so beveled spline ends are facing stop ring.
Ensure sleeve tooth is aligned (centered) over each synchronizer strut. Gear clash will occur if strut and
sleeve teeth are misaligned. Install NEW pads on mode fork. Engage mode fork in synchronizer sleeve.
Install mainshaft and fork assembly in case. Ensure mode fork shift rail is seated in both range fork
bushings.
9. Install output shaft and drive chain assembly. Install mode spring on shift rail. Using bearing driver,
install output shaft rear bearing. Lubricate bearing after installation. Install seal in oil pump feed housing.
Install oil pump in housing. Tighten to specification.
10. Install oil pick-up tube "O" ring in oil pump. Prime oil pump by pouring ATF into pump through pick-up
tube opening. Install oil pump and pick-up tube in case. Ensure oil screen is properly positioned. See Fig.
3 . Install magnet in front case. Apply 1/8" bead of silicone sealer to front case. Install rear case. Tighten
to specification. See TORQUE SPECIFICATIONS . Ensure mainshaft splines are engaged with oil
pump inner gear and a washer is used on bolts at dowel locations.
11. Install rear bearings in retainer. Apply 1/8" bead of silicone sealer and install retainer to case. Install rear
retainer snap ring. Install extension housing. Install front companion yoke. Install NEW gasket on
vacuum switch. Install vacuum switch in case. Fill transfer case with Dexron III.

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 1997 Chevrolet S10 Pickup
1997 TRANSFER CASES General Motors Corp. New Venture 231 Overhaul

Fig. 3: Identifying Oil Pump Screen Position

Courtesy of CHRYSLER CORP.

TORQUE SPECIFICATIONS
TORQUE SPECIFICATIONS
Application Ft. Lbs. (N.m)
Companion Flange Nut 80 (108)
Detent Plug 11 (15)
Drain & Fill Plug 30-40 (41-54)
Extension Housing Bolt 26-34 (35-46)
Front Bearing Retainer Bolt 14 (19)
Front Case-to-Rear Case Bolt 23 (31)
Range Lever Nut 20-25 (27-34)
Rear Bearing Retainer Bolt 20-25 (27-34)
Rear Crossmember 30 (41)
Shift Lever Lock Bolt 10 (14)
Shift Selector Lever Nut 20 (27)
Speed Sensor Bolt 23 (31)
Transfer Case-to-Transmission Nut 26 (35)
Vacuum Switch 17 (23)

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 1997 Chevrolet S10 Pickup
1997 TRANSFER CASES General Motors Corp. New Venture 231 Overhaul

INCH Lbs. (N.m)

Control Cable Lock Nut 18 (2)

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