Pontiac Fiero 1984-1988 Repair Guide

4-Speed 76mm Isuzu (MG1) Overhaul

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DISASSEMBLY





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Fig. Fig. 1 Exploded view of the 4-speed (76mm) Isuzu manual transaxle



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Fig. Fig. 2 Isuzu 4-speed (76mm) manual transaxle component list



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Fig. Fig. 3 Remove the ring gear and differential assembly ...



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Fig. Fig. 4 ... then place the shifter shaft in neutral. Bend back the tab on the lock and unfasten the bolt so that the shift shaft may be disengaged from the synchronizer forks



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Fig. Fig. 5 Disengage the guide pin and interlock bracket to remove the reverse shift link



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Fig. Fig. 6 Unfasten the reverse idler gear lockbolt, then remove the gearshaft and spacer as an assembly



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Fig. Fig. 7 View of the shift shaft and fork assembly

  1. Remove the transaxle assembly from the vehicle and place on a suitable work stand.
  2.  
  3. Remove the fifteen clutch cover-to-transaxle attaching bolts. Tap the clutch cover with a rubber hammer to work it loose.
  4.  
  5. Remove the ring gear/differential assembly.
  6.  
  7. Position the shifter shaft in the neutral position so the shifter moves freely and is not engaged in any drive gear.
  8.  
  9. Bend back the tab on the lock and remove the bolt from the shifter shaft. Remove the shifter shaft and fork from the synchronizer forks.
  10.  
  11. Remove the reverse shift fork by disengaging the guide pin and interlock bracket.
  12.  
  13. Remove the lock bolt securing the reverse idler gear shaft. Remove the gear/shaft and spacer as an assembly.
  14.  
  15. Remove the detent shift lever and interlock assembly. Leave the shift forks engaged with the synchronizers.
  16.  
  17. Grasp the input and output shafts and then lift them as an assembly from the case. Note the positions of the shift forks to aid in reinstallation. Remove shift forks.
  18.  

Shaft Disassembly


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Fig. Fig. 8 Use a press to remove the 3rd gear synchronizer and gear



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Fig. Fig. 9 Use tool J-26946 or its equivalent to remove the right hand bearing



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Fig. Fig. 10 Press the 2nd and 3rd gears from the output shaft and remove the brass blocker rings



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Fig. Fig. 11 Place tool J-22227 or its equivalent on the right hand bearing and press out the bearing using pilot tool J-26943

The terms R.H. and L.H. refer to the installed position on the vehicle. RH refers to the end nearest the clutch and the LH refers to the end farthest from the clutch.

INPUT SHAFT
  1. Slide the LH bearing and 4th gear from the input shaft.
  2.  
  3. Remove the brass blocker ring and snapring from the 3-4 synchronizer.
  4.  
  5. Using a support plate behind 3rd gear, press the 3rd gear off the shaft.
  6.  
  7. Remove the RH bearing from the shaft using tool No. J-26946.
  8.  

OUTPUT SHAFT
  1. Using support plates behind the 4th gear, press on the end of the output shaft to remove the 4th gear and the LH bearing.
  2.  
  3. Remove the 3rd gear snapring.
  4.  
  5. Slide the 1-2 synchronizer into the first gear position to allow the press plates to support the 2nd gear. Press the 2nd speed gear and 3rd gear from the output shaft and remove the brass blocker rings.
  6.  
  7. Remove the snapring retaining the 1-2 synchronizer.
  8.  
  9. Using press plates behind the 1st speed gear, then press the 1st gear and 1-2 synchronizer from the output shaft.
  10.  
  11. Install tool No. J-22227-A on the RH bearing and remove the bearing by pressing on tool No. J-26943 pilot.
  12.  

SYNCHRONIZER OVERHAUL


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Fig. Fig. 12 Synchronizer assembly components

  1. Carefully pry out both synchronizer key springs from the synchronizer.
  2.  
  3. Separate the hub, sleeve and 3 keys after noting their positions for reinstallation.
  4.  
  5. Clean all parts with solvent.
  6.  
  7. Assemble the hub to the sleeve with the extruded lip on the hub directed away from the shift fork groove in the sleeve and align the assembly as previously marked.
  8.  
  9. Install the retaining ring, and carefully pry the ring back and insert the keys, one at a time. Make sure to position the ring so it is captured by the keys.
  10.  
  11. Install the ring on the opposite side with the open segment of the ring with the open segment on the other side.
  12.  

Shaft Reassembly

Before assembling the shafts, apply a coat of specified lubricant to the thrust washers, all gears and washers.

INPUT SHAFT


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Fig. Fig. 13 Use a press to install the 3rd gear and 3-4 synchronizer

  1. Install RH bearing onto shaft using tool J-28406.
  2.  
  3. Place the 3rd gear onto the shaft, install the brass blocker ring onto the gear cone and install the 3-4 synchronizer, using the appropriate cylinder to contact the hub near the shaft. Do not press on the sleeve portion. Both synchronizers hubs are a press fit to the shaft.
  4.  
  5. Install the snapring to retain 3-4 synchronizer. The beveled edges should be away from the synchronizer for later access with the snapring pliers.
  6.  
  7. Install the brass blocker ring.
  8.  
  9. Slide the 4th gear onto shaft, position it toward the 3-4 synchronizer and slide the LH bearing onto the shaft.
  10.  

OUTPUT SHAFT
  1. Install the RH bearing onto the shaft.
  2.  
  3. Place the 1st gear onto the shaft near the 1-2 synchro. Install the brass blocker ring onto the cone, install the 1-2 synchro using the appropriate cylinder to press to the hub. Do not press on the sleeve.
  4.  
  5. Install the snapring to retain 1-2 synchro. and install blocker ring.
  6.  
  7. Place the 2nd gear onto the shaft, press 3rd gear onto shaft with its hub towards the 4th gear.
  8.  
  9. Install the snapring to retain 3rd gear.
  10.  
  11. Press the 4th gear onto the shaft with its hub towards the 3rd gear. Install the LH bearing onto the shaft using tool No. J-26942.
  12.  

Case Reassembly
  1. Place the input and output shaft together and install the two shift forks on a bench.
  2.  
  3. Hold the shafts as an assembly and carefully lower into the transaxle case.
  4.  
  5. Place the interlock bracket onto the guide pin tool J-28411. Make sure the bracket engages the fingers on the shift forks.
  6.  
  7. Use a straight edge on both sides of the interlock to determine if the detent is out of alignment with the interlock.
  8.  

The straight edge should rest on both side of the interlock without interference on either side.

    1. Place the detent and interlock in a vise and with light pressure, push it into alignment.
    2.  
    3. Loosen the nut securing the detent spring to the interlock. The spring is slotted for proper alignment.
    4.  
    5. Tighten the nut while exerting light pressure on the spring with your thumb.
    6.  
    7. Check detent alignment with a straight edge.
    8.  


  1. Install detent lever into interlock. Install shifter shaft through the interlock bracket and the detent lever but do not extend any further.
  2.  
  3. Install the reverse shift fork onto guide pin. Install the reverse idler gear and shaft into position. The long end points upward. Install the spacer onto the shaft.
  4.  
  5. The flat on the reverse idler shaft faces the input gear.
  6.  
  7. Fully install the shifter shaft through the reverse shift fork until it pivots into the inhibitor spring.
  8.  
  9. Remove the dummy shaft, place shaft in neutral position, install the bolt and lock through the detent shift lever and bend the tab of the lock over the bolt head.
  10.  
  11. Install the shift fork through the synchro forks and into the bores in the case and install the magnet.
  12.  
  13. Apply a thin bead of anaerobic sealant (not RTV) to the clutch cover, then carefully install the cover onto the transaxle case using the dowel pins to guide the cover into position. Gently tap the housing with a rubber hammer to ensure the parts are seated.
  14.  
  15. Install the fifteen attaching bolts and torque to 16 ft. lbs. (21 Nm).
  16.  
  17. Torque the idler shaft retaining bolts in case to 16 ft. lbs. (21 Nm).
  18.  
  19. Test the gear ranges by shifting the shift shaft. If freedom is not felt, remove the clutch cover to check for problem.
  20.  
  21. Install all other external parts needed before transaxle installation.
  22.  
  23. Install the transaxle assembly into the vehicle as outlined in the "Transaxle and Cradle" procedures in this section.
  24.  

 
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