GM Full-Size Trucks 1970-1979 Repair Guide

New Process Model 203 Overhaul

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The New Process Model 203 transfer case is a full-time 4WD unit that operates in 4WD at all times. The unit incorporates a differential similar to axle differentials; compensating for different speeds of the front and rear axles resulting from varying speeds while turning and operating over different surfaces.

There are five shift positions with this transfer case; Neutral, High and High Lock, and Low and Low Lock. The Lock positions are used under low traction conditions. In the Lock position, the differential action of the transfer case is eliminated, by locking the front and rear output shafts together. In this mode, neither the front or rear axle can rotate independently of the other.

CASE DISASSEMBLY



  1. Loosen rear output shaft flange retaining nut and remove front output shaft flange and washer.
  2.  
  3. Tap the front output shaft dust seal away from case assembly. Remove front output shaft bearing retainer and gasket.
  4.  
  5. Position transfer case assembly on blocks with input shaft facing downward.
  6.  
  7. Remove rear output shaft assembly from transfer case. Slide the differential carrier off the shaft.
  8.  
  9. Place a 1 1 / 2 -2 in. band type hose clamp on input shaft to retain bearings.
  10.  
  11. Lift shift rail and driveout pin retaining shift fork.
  12.  
  13. Remove shift rail poppet ball plug, gasket and ball from case. Use a magnet to remove poppet ball.
  14.  
  15. Push shift rail down, lift up on lockout clutch and remove shift fork from clutch assembly.
  16.  
  17. Remove front output shaft rear bearing retainer. It may be necessary to gently tap front of shaft or cautiously pry retainer from case. Make certain that no roller bearings are lost from rear cover.
  18.  
  19. When necessary, remove rear bearing by pressing.
  20.  
  21. Pry front output shaft front bearing from lower side of case.
  22.  
  23. Remove front output shaft assembly from case.
  24.  
  25. Lift intermediate housing from range box, after removing bolts.
  26.  
  27. Remove chain from intermediate housing.
  28.  
  29. Remove lockout clutch, drive gear and input shaft from range box.
  30.  
  31. Install a 1 1 / 2 -2 in. band type hose clamp on end of input shaft to retain roller bearings.
  32.  
  33. Pull up on shift rail and remove rail from link.
  34.  
  35. Lift input shaft assembly from range box.
  36.  

CASE ASSEMBLY



  1. Position range box with input gear side down, on wood blocks.
  2.  
  3. Place gasket on input housing.
  4.  
  5. Install lockout clutch and drive sprocket on input shaft assembly. Install a 2 in. band type hose clamp on end of input shaft to prevent loss of bearings during installation.
  6.  
  7. Place input shaft, lockout clutch and drive sprocket in range box. Align tab on bearing retainer with notch in gasket.
  8.  
  9. Engage lockout clutch shift rail to the connector link. Position rail in housing bore and turn shifter shaft lowering rail into the housing. This will prevent the link and rail from becoming disconnected.
  10.  
  11. Place the drive chain in housing with the chain around the outer wall.
  12.  
  13. Secure the chain housing to the range box. Be sure that the shift rail engages the channel of the housing. Place the chain on the input drive sprocket.
  14.  
  15. Place the front output sprocket in transfer case. Turn the clutch drive gear to assist in positioning chain on sprocket.
  16.  
  17. Position the shift fork and rail on the clutch assembly. Install the clutch assembly completely into the drive sprocket. Insert retaining pin in shift fork and rail.
  18.  
  19. Install front output bearing, gasket, retainer, bolts, flange, gasket, seal, washer and retaining nut.
  20.  
  21. If rear bearing was removed from front output shaft, press a new bearing into the outside face of cover until bearing is flush with opening.
  22.  
  23. Install front output shaft, rear bearing, retainer, gasket and bolts.
  24.  
  25. Slip differential carrier assembly on the input shaft. Bolts on carrier must face rear of shaft.
  26.  
  27. Load bearings in pinion shaft, install rear output housing assembly, gasket and bolts.
  28.  
  29. Install a dial indicator on the rear housing. The indicator must contact the end of the output shaft. While holding the rear flange, rotate the front output shaft and find the highest point of gear hop. Reset indicator and with rear output shaft at high point, pull up on the end of the shaft to determine end-play. Remove indicator and install shim pack to control end-play to between 0-0.005 in. The shim pack is positioned on the shaft in front of the rear bearing. Check for binding of rear output shaft.
  30.  
  31. Insert lockout clutch shift rail poppet ball, spring and screw plug in transfer case.
  32.  
  33. Install poppet plate spring, gasket and plug, if they were not previously installed.
  34.  
  35. Install shift levers on the range box, if these were not left on vehicle.
  36.  
  37. Tighten all bolts, locknuts and plugs to the following specifications:
  38.  



Adapter-to-case: 38 ft. lbs. (51 Nm)
 
Adapter-to-transmission: 40 ft. lbs. (54 Nm)
 
Upper case-to-frame: 50 ft. lbs. (68 Nm)
 
Lower case-to-frame: 65 ft. lbs. (88 Nm)
 
Shift lever nuts: 25 ft. lbs. (34 Nm)
 
Shift lever rod-to-swivel: 50 ft. lbs. (68 Nm).
 
Shift lever locking arm nut: 150 inch lbs. (17 Nm)
 
Skid plate nuts: 45 ft. lbs. (61 Nm)
 
Crossmember nuts: 45 ft. lbs. (61 Nm)
 
Adapter mount bolts: 25 ft. lbs. (34 Nm)
 
Intermediate case-to-range box: 30 ft. lbs. (41 Nm)
 
Front output bearing retainer: 30 ft. lbs. (41 Nm)
 
Output shaft yoke nut: 150 ft. lbs. (203 Nm)
 
Differential assembly screws: 45 ft. lbs. (61 Nm)
 
Rear output shaft housing: 30 ft. lbs. (41 Nm)
 
Poppet ball retainer nut: 15 ft. lbs. (20 Nm)
 
PTO cover bolts: 15 ft. lbs. (20 Nm)
 
Front input bearing retainer: 20 ft. lbs. (27 Nm)
 
Filler plug: 25 ft. lbs. (34 Nm)
 

  1. Fill transfer case with specified lubricant until the proper level is reached. Secure filler plug.
  2.  

SUBASSEMBLY OVERHAUL



Lockout Clutch
DISASSEMBLY
  1. Remove front side gear from input shaft assembly.
  2.  
  3. Remove thrust washer, roller bearings and spacers from front side gear bore. The position of the spacers must be noted.
  4.  
  5. Remove the snapring which holds the drive sprocket to clutch assembly. Slip the drive sprocket from the front side gear.
  6.  
  7. Remove the lower snapring.
  8.  
  9. Remove sliding gear, spring and spring cup washer from the front side gear.
  10.  
  11. Thoroughly clean and inspect all component parts. Replace any component that is worn or defective.
  12.  

ASSEMBLY
  1. Place spring cup washer, spring and sliding clutch gear on front side gear.
  2.  
  3. Secure sliding clutch to front side gear with a snapring.
  4.  
  5. Spread petroleum jelly on front side gear and install roller bearings and spacers.
  6.  
  7. Place thrust washer in gear end of front side gear.
  8.  
  9. Slide drive sprocket on clutch splines and secure with snapring.
  10.  

Differential Carrier
DISASSEMBLY
  1. Separate differential carrier sections and lift out pinion gear and spider assembly.
  2.  
  3. Note that undercut side of pinion gear spider faces toward front of side gear.
  4.  
  5. Remove pinion thrust washers, pinion roller washer gears and roller bearings from spider unit.
  6.  
  7. Thoroughly clean and inspect all component parts. Replace any component that is worn or damaged.
  8.  

ASSEMBLY
  1. Spread petroleum jelly on pinion gears and install roller bearings.
  2.  
  3. Position on the leg of each spider, pinion roller washer, pinion gear and thrust washer.
  4.  
  5. Position the spider assembly in front half of the carrier. The undercut surface of the spider thrust surface face downward or toward teeth.
  6.  
  7. Secure the carrier halves together. Make certain the marks are aligned. Tighten all bolts to specifications. See the above list.
  8.  

Input Shaft
DISASSEMBLY
  1. Remove thrust washer and spacer from shaft.
  2.  
  3. Remove bearing retainer assembly from input shaft.
  4.  
  5. Hold low speed gear and lightly tap shaft from gear. Note the position of the thrust washer pins in input shaft.
  6.  
  7. Remove snapring holding input bearing in retainer using a screw driver. Lightly tap rear bearing out of retainer.
  8.  
  9. Remove pilot roller bearing and O-ring from end of input shaft.
  10.  
  11. Thoroughly clean and inspect all component parts. Replace any component that is worn or damaged.
  12.  

ASSEMBLY
  1. Tap or press input bearing into retainer. Be sure that ball loading slots are toward concave side of retainer. Install securing snap ring. Make certain that selective snapring of proper thickness is used to provide tightest fit.
  2.  
  3. Position low speed gear on shaft, clutch end facing gear end of input shaft.
  4.  
  5. Place thrust washers on input shaft, align slot in washer with pin in shaft. Slide or tap washers into position.
  6.  
  7. Place input bearing retainer on shaft and secure with snapring. Snaprings are selective. Use snapring that provides tightest fit.
  8.  
  9. Slip spacer and thrust washer on shaft and align with locating pin.
  10.  
  11. Spread heavy grease on end of shaft and install roller bearings.
  12.  
  13. Install rubber O-ring at end of shaft.
  14.  

Range Box
DISASSEMBLY
  1. Remove poppet plate spring, plug and gasket.
  2.  
  3. Remove clutch fork and sliding gear by disengaging sliding clutch gear from input gear.
  4.  
  5. Remove upper shift lever from shifter shaft.
  6.  
  7. Remove snapring and lower shift lever.
  8.  
  9. Push shifter shaft assembly down and remove lockout clutch connector link. The long end of connector link engages poppet plate.
  10.  
  11. Remove shifter shaft assembly and separate shafts. Remove O-rings.
  12.  
  13. When necessary to remove poppet plate, drive pivot shaft out and remove plate and spring from bottom of case.
  14.  
  15. Remove input gear bearing retainer and seal assembly. Release snapring from retainer and tap bearing out of assembly.
  16.  
  17. Release snapring holding input shaft bearing to shaft and remove bearing.
  18.  
  19. Remove countershaft from cluster gear and case assembly from intermediate case side. Remove cluster gear assembly from range box.
  20.  
  21. Remove cluster gear thrust washers from case.
  22.  
  23. Thoroughly clean and inspect all component parts. Replace any component that is worn or damaged.
  24.  

ASSEMBLY
  1. Spread heavy grease in cluster bore and using proper tool install roller bearings and spacers.
  2.  
  3. Spread heavy grease on case and install thrust washers. Engage tab on thrust washers with slot in case.
  4.  
  5. Place cluster gear assembly in case and install countershaft through front of range box and into gear assembly. Flat face of countershaft must be aligned with case gasket.
  6.  
  7. Place bearing on input gear shaft with snapring groove facing out, install a new retaining ring. Insert input gear and bearing in housing. The retaining ring used in this operation is a select fit. Use ring that provides the tightest fit.
  8.  
  9. Secure input gear and bearing with a snapring.
  10.  
  11. Match up oil slot in retainer with drain hole in case and insert input gear bearing retainer and gaskets. Install bolts and tighten to 20 ft. lbs. (27 Nm).
  12.  
  13. Spread sealant on pin and install poppet pin and pivot pin in housing.
  14.  
  15. Lubricate and install new O-rings on inner and outer shifter shafts.
  16.  
  17. Insert shifter shafts in housing and engage long end of lockout clutch connector link with outer shifter shaft. Complete this operation before assembly bottoms out.
  18.  
  19. Install lower shift lever and retaining ring.
  20.  
  21. Install upper shift lever and shaft retaining nut.
  22.  
  23. Install shift fork and sliding clutch gear. Push fork up into shifter shaft and engage poppet plate. Move sliding clutch gear onto input shaft gear.
  24.  
  25. Insert poppet plate spring, gasket and plug in housing top. Make certain that spring engages poppet plate.
  26.  

Input Gear Bearing
REPLACEMENT
  1. Remove bearing retainer and gasket from housing.
  2.  
  3. Remove and discard snapring holding bearing in retainer.
  4.  
  5. Pry bearing from case and remove from shaft.
  6.  
  7. Inspect input gear and bearing retainer for damage or wear. Replace if necessary.
  8.  
  9. Place new bearing and snapring on input gear. Using a soft hammer, tap bearing into position. Secure snapring.
  10.  
  11. Insert bearing retainer into housing and secure with attaching bolts. Tighten the bolts to 20 ft. lbs. (27 Nm).
  12.  

Input Gear Seal
REPLACEMENT
  1. Remove bearing retainer from housing.
  2.  
  3. Remove seal from retainer by prying.
  4.  
  5. Place new seal on retainer and install with proper seal driver.
  6.  
  7. Install bearing retainer in housing and secure with attaching bolts. Tighten the bolts to 20 ft. lbs. (27 Nm).
  8.  

Rear Output Shaft Housing
DISASSEMBLY
  1. Remove speedometer driven gear from housing.
  2.  
  3. Remove rear output flange and washer, if they have not been removed previously.
  4.  
  5. Using a soft hammer tap on flange end of pinion and remove the pinion. If speedometer drive gear does not come off with pinion reach into case and remove.
  6.  
  7. Remove old seal from bore with suitable prying tool.
  8.  
  9. Remove snap ring retaining rear output rear bearing.
  10.  
  11. Tap bearing out of housing.
  12.  
  13. Install a long drift into rear opening of housing and drive out front output bearing. Remove seal and discard.
  14.  

ASSEMBLY
  1. Spread grease on front bearing seal and place in bore. Place bearing in bore and press until it bottoms in housing.
  2.  
  3. Using a soft hammer tap rear bearing into place. Secure with proper snapring. Snaprings are selective, use the one that provides the tightest fit.
  4.  
  5. Place rear seal in bore and drive into position with suitable tool. When seal is in position it should be approximately 1 / 8 - 3 / 16 in. below the housing face.
  6.  
  7. Place speedometer drive gear on output shaft with shims of approximately 0.050 in. thickness. Insert output shaft into carrier through housing front opening.
  8.  
  9. Install flange and washer on output shaft. Leave retaining nut loose until shim requirements are known.
  10.  
  11. Install speedometer driven gear.
  12.  

Front Output Shaft Bearing Seal
REPLACEMENT
  1. Remove old seal from retainer bore.
  2.  
  3. Inspect and clean retainer.
  4.  
  5. Spread sealer on outer edge of new seal.
  6.  
  7. Place new seal in retainer bore and drive into position with proper tool.
  8.  

Front Output Bearing
REPLACEMENT
  1. Remove rear cover from case assembly and discard gasket.
  2.  
  3. Press old bearing from cover.
  4.  
  5. Place new bearing on outside face of cover. Cover bearing with a wood block and press into cover until bearing is flush with opening.
  6.  
  7. Place gasket on transfer case and tap cover into position using a soft hammer. Secure the cover with the attaching bolts and tighten to 30 ft. lbs. (41 Nm).
  8.  

 
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