Isuzu Cars and Trucks 1981-1991

5-Speed Overhaul 2-Wheel Drive P'up Rear Wheel Drive Impulse and I-Mark

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BEFORE DISASSEMBLY

Cleanliness is an important factor in the overhaul of the manual transmission. Before opening up this unit, the entire outside of the transmission assembly should be cleaned, preferably with a high pressure washer such as a car wash spray unit. Dirt entering the transmission internal parts will negate all the time and effort spent on the overhaul. During inspection and reassembly all parts should be thoroughly cleaned with solvent then dried with compressed air. Wiping cloths and rags should not be used to dry parts.

Wheel bearing grease, used to hold thrust washers and lube parts, should not be used. Lube seals with clean SAE 30 weight engine oil and use ordinary unmedicated petroleum jelly to hold the thrust washers, needle bearings and to ease the assembly of seals, since it will not leave a harmful residue as grease often will. Do not use solvent on neoprene seals, friction plates if they are to be reused, or thrust washers.

Before installing bolts into aluminum parts, always dip the threads into clean transmission fluid. Anti-seize compound can also be used to prevent bolts from galling the aluminum and seizing. Always use a torque wrench to keep from stripping the threads. Take care when installing new O-rings, especially the smaller O-rings. The internal snaprings should be expanded and the external rings should be compressed, if they are to be reused. This will help insure proper seating when installed.

DISASSEMBLY
  1. Remove the clutch shift block and release bearing.
  2.  
  3. Remove the clutch fork, speedometer driven gear and front cover with oil seal.
  4.  
  5. Remove the front bearing Belleville spring, counter gear snapring and front bearing snapring.
  6.  
  7. Remove the rear housing with oil seal.
  8.  
  9. Pull the intermediate plate with gear assemblies out of the transmission case.
  10.  



Click image to see an enlarged view

Fig. Major component disassembly MUA 5-speed

Shift Quadrant and Lever
IMPULSE
  1. Remove the upper change lever, spring stopper, retainer and spring.
  2.  
  3. Remove the outer spherical cage, U-bolt nuts and select stop spring.
  4.  
  5. Remove the select stop U-bolt, inner spherical cage from the pivot case.
  6.  
  7. Remove the joint bolt, lock washer and lower change lever.
  8.  
  9. Remove the pivot stopper, reverse select stopper, bracket mounting bolt, pivot stopper bolt and bracket.
  10.  
  11. Remove the dust cover, joint bolt, rear control rod and dust cover boot.
  12.  
  13. Remove the neutral switch, gasket, spring pin, internal lever, front control rod, oil seal and control rod boot.
  14.  



Click image to see an enlarged view

Fig. Shift quadrant box Impulse

To assemble

  1. Install the control rod boot, oil seal, front control rod, internal lever, spring pin, neutral switch gasket and neutral switch.
  2.  
  3. Install the dust cover boot, rear control rod, joint bolt, dust cover and bracket.
  4.  
  5. Install the pivot stopper bolt, bracket mounting bolt, reverse select stopper and pivot stopper.
  6.  
  7. Install the lower change lever, lock washer, joint bolt and pivot case.
  8.  
  9. Install the inner spherical cage, select stop U-bolt, select stop spring, U-bolt nuts and outer spherical cage.
  10.  
  11. Install the lever spring, retainer, spring stopper and upper change lever.
  12.  

Detent, Shift Fork and Interlock Pin
DISASSEMBLY
  1. Remove the detent spring plate, springs and detent balls using a magnet.
  2.  
  3. Remove the 5th/rev shift arm and rod.
  4.  
  5. Remove the 1st/2nd shift rod, 3rd/4th shift rod, 3rd/4th shift arm and 1st/2nd shift arm.
  6.  
  7. Remove the interlock pin.
  8.  



Click image to see an enlarged view

Fig. Low/rev thrust washer oil groove position MUA 5-speed, top is low

ASSEMBLY
  1. Install the 1st/2nd shift arm, 3rd/4th shift arm, interlock pin, 3rd/4th shift rod and 1st/2nd shift rod. Use a round bar against the shift rods to protect against damage then drive in the spring pins.
  2.  
  3. Install the 5th/rev shift arm and rod. Drive in spring pin.
  4.  
  5. Install the detent balls, springs and spring plate. Torque the retaining bolts to 15 ft. lbs. (20 Nm).
  6.  

Reverse and 5th Gear
DISASSEMBLY
  1. Remove the mainshaft bearing snapring, speedometer drive gear and lock ball, bearing spacer and bearing.
  2.  
  3. Remove the thrust ring, thrust ring retaining ring, thrust washer and lock ball.
  4.  
  5. Remove the reverse counter gear nut and washer.
  6.  
  7. Remove the counter gear bearing and 5th counter gear using a jaw puller J22888 or equivalent.
  8.  
  9. Remove the reverse counter gear.
  10.  
  11. From the mainshaft, remove the 5th gear, 5th blocker ring and needle bearings.
  12.  
  13. Remove the mainshaft locknut and washer using a locknut wrench J29768 or equivalent.
  14.  
  15. Remove the 5th/rev synchronizer assembly as an assembly.
  16.  
  17. Remove the reverse gear, needle bearings and bearing collar.
  18.  
  19. Remove the reverse gear thrust washer and the counter gear locknut.
  20.  
  21. After removing the locknut, remove the thrust washer, reverse idler gear, thrust washer, reverse shaft retaining bolt and reverse shaft.
  22.  
  23. Insert snapring pliers into the counter gear bearing snapring hole located in the intermediate plate. Remove the bearing snapring.
  24.  
  25. Remove the mainshaft bearing snapring in the same fashion as above.
  26.  
  27. Remove the intermediate plate from the shafts.
  28.  

ASSEMBLY
  1. Install the reverse shaft-to-intermediate plate and torque the retaining bolt to 15 ft. lbs. (20 Nm).
  2.  
  3. Install the mainshaft and counter shaft bearing snapring into the intermediate plate.
  4.  
  5. Install the reverse idler gear thrust washer, reverse idler gear, thrust washer and reverse gear locknut. Torque the locknut to 80 ft. lbs. (108 Nm).
  6.  
  7. Install the mainshaft thrust washer onto the mainshaft with the oil groove facing the front of the transmission.
  8.  
  9. Install the reverse gear bearing collar, needle bearings and reverse gear.
  10.  
  11. Install the 5th/rev synchronizer assembly so that sleeve heavy chamfer and insert short side is facing the rear of the transmission.
  12.  
  13. Install the mainshaft locknut and washer using the locknut wrench J36629. Torque the locknut to 87 ft. lbs. (118 Nm).
  14.  
  15. Install the 5th gear needle bearings, 5th blocker ring and 5th gear.
  16.  
  17. Install the 5th gear thrust washer and lock ball.
  18.  
  19. Install the reverse counter gear onto the counter shaft, 5th counter gear, counter shaft bearing, washer and locknut. Torque the locknut to 80 ft. lbs. (108 Nm).
  20.  
  21. Install the thrust washer thrust ring and thrust ring retaining ring onto the mainshaft.
  22.  
  23. Install the thrust ring snapring onto the mainshaft.
  24.  
  25. Install the mainshaft bearing, bearing spacer, speedometer drive gear and lock ball and bearing snapring.
  26.  

Top Shaft, Mainshaft and Counter Gear
DISASSEMBLY
  1. Remove the top gear shaft snapring, top shaft and needle bearings. Remove the shaft bearing using a bench press and bearing remover.
  2.  
  3. Remove the top gear blocker ring, mainshaft snapring and the 3rd/4th synchronizer as an assembly. Remove the 3rd blocker ring.
  4.  
  5. Remove the 3rd gear and needle bearings.
  6.  
  7. Remove the mainshaft bearing using a press and bearing remover.
  8.  
  9. Remove the 1st gear thrust washer, 1st gear, needle bearings and bearing collar.
  10.  
  11. Remove the 1st blocker ring and 1st/2nd synchronizer as an assembly.
  12.  
  13. Remove the 2nd blocker ring, 2nd gear, and needle bearings from the mainshaft.
  14.  
  15. Remove the front and rear counter shaft bearings with a bench press and bearing remover.
  16.  



Click image to see an enlarged view

Fig. Mainshaft, cluster gear and top gear assembly MUA 5-speed

ASSEMBLY
  1. Install the 2nd gear needle bearings into the mainshaft. Install the 2nd gear so the teeth face the rear of the transmission.
  2.  
  3. Install the 2nd blocker ring and the 1st/2nd synchronizer as an assembly. The outside sleeve heavy chamfering 30and#x00B0; must face to the rear of the transmission. Install the 1st blocker ring.
  4.  
  5. Using a press and a collar installer J33851, install the needle bearing collar into the 1st gear.
  6.  
  7. Install the 1st gear needle bearings and 1st gear onto the mainshaft with the teeth facing the front of the transmission.
  8.  
  9. Install the 1st gear thrust washer with the oil groove facing forward.
  10.  
  11. Install the mainshaft bearing using a press and bearing installer.
  12.  
  13. Install the 3rd gear needle bearings and 3rd gear with the teeth facing forward.
  14.  
  15. Install the 3rd blocker ring and 3rd/4th synchronizer as an assembly. The sleeve light chamfer and clutch hub heavy boss must face rearward.
  16.  
  17. Install the mainshaft snapring and measure the clearance between the mainshaft and the snapring. There are four snapring sizes to pick from.
  18.  
  19. Install the top gear shaft needle bearings and top blocker ring onto the top gear shaft.
  20.  
  21. Install the top gear shaft bearing with a press and bearing installer. The snapring groove must face forward.
  22.  
  23. Install the top shaft snapring.
  24.  
  25. Using a press and bearing installer, install the counter shaft front bearing, snapring and rear bearing.
  26.  

COMPONENT INSPECTION
  1. Using a micrometer, check the shift arm thickness where it rides on the synchronizer. 1st/2nd = 0.307 and 190.276 in. (7.8 and 197.0mm), 3rd/4th = 0.280 and 190.256 in. (7.1 and 196.5mm) and 5th/rev = 0.268 and 190.248 in. (6.8 and 196.3mm).
  2.  
  3. Using a inside slide ruler, check the free length of the detent springs. 1.01 and 190.93 in. (25.6 and 1923.6mm).
  4.  
  5. Using a spring tension tester, check the detent spring tension. 14.0 and 1915.0 lbs. (6.3 and 196.7 kg).
  6.  
  7. Using a feeler gauge, check the clearance between the blocker ring and gear. Standard clearance for 1st/2nd = 0.067 and 190.032 in. (1.7 and 190.8mm), 3rd/4th = 0.059 and 190.032 in. (1.5 and 190.8mm) and 5th/rev = 0.051 and 190.032 in. (1.3 and 190.8mm).
  8.  
  9. Using a feeler gauge, check the clearance between the blocker rings and inserts. Standard clearance 0.138 and 190.158 in. (3.51 and 194.00mm).
  10.  
  11. Using a feeler gauge, check the clearance between the clutch hub and inserts. Standard clearance 0.0004 and 190.012 in. (0.01 and 190.3mm).
  12.  
  13. Using a dial indicator and holding fixture, check the mainshaft run-out. Limit 0.0012 in. (0.03mm).
  14.  
  15. Using an inside T-gauge, check the gear inside diameter. Low gear 1.773 and 191.777 in. (45.0 and 1945.1mm). 2nd/3rd gear 1.615 and 191.619 in. (41.0 and 1941.1mm).
  16.  
  17. Using a micrometer, check the clearance between the bushing and idler gear shaft. Standard clearance 0.0016 and 190.0059 in. (0.041 and 190.15mm).
  18.  
  19. Using a dial indicator, check the spline play. Clutch hub 0.0 and 190.0079 in. (0.0 and 190.20mm) and reverse gear 0.0024 and 190.0078 in. (0.062 and 190.200).
  20.  
  21. Replace components that do not meet specifications.
  22.  



Click image to see an enlarged view

Fig. Checking trust washer clearance MUA 5-speed

TRANSMISSION ASSEMBLY
  1. Install the intermediate plate with the gear assemblies into the main housing.
  2.  
  3. Install the rear housing with oil seal. Torque the housing bolts to 15 ft. lbs. (20 Nm).
  4.  
  5. Install the top gear shaft and counter shaft snaprings after the gear shafts are installed in the housing.
  6.  
  7. Install the Belleville spring and front cover with a new oil seal. Torque the cover retaining bolts to 15 ft. lbs. (20 Nm).
  8.  
  9. Install the speedometer driven gear, clutch shift fork, shift block and release bearing.
  10.  

 
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