GM Full-Size Trucks 1970-1979 Repair Guide

Adjustments

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LOW BAND



This procedure applies to Powerglide transmissions only.

  1. Raise and support the vehicle with jackstands.
  2.  
  3. Place the selector lever in Neutral.
  4.  
  5. Remove the protective cap from the low band adjusting screw.
  6.  
  7. Loosen the adjusting screw locknut 1 / 4 turn and hold it in this position with a wrench.
  8.  
  9. Using an inch pound torque wrench, adjust the band adjusting screw to 70 inch lbs. (7.8 Nm), and back the screw off 4 complete turns for a band that has been in operation 6,000 miles or more; or 3 complete turns for a band that has been in operation less than 6,000 miles.
  10.  

The back-off figure is not approximate; it must be exact.

  1. Tighten the adjusting screw locknut.
  2.  
  3. Lower the vehicle and road test.
  4.  

SHIFT LINKAGE



Powerglide Transmissions

The shift tube and selector linkage must be free in the mast jacket.

  1. Set the transmission lever in Drive (D).
  2.  

Do not be guided by the position of the needle. Determine Drive by shifting the lever all the way to the right of the Low (L) detent. Rotate it back to the left, one detent, to Drive (D).

  1. Attach the control rod to the lever and inner lever of the shaft assembly with the retainers.
  2.  
  3. Assemble the swivel, clamp, grommet, bushing, washers and nut loosely on the selector lever.
  4.  
  5. Attach the control rod to the outer lever of the shaft assembly with the retainer.
  6.  
  7. Place the selector lever tang in the Neutral drive gate of the selector plate assembly and insert the control rod into the swivel.
  8.  
  9. Rotate the lever clockwise viewed looking down the steering column, until the tang contacts the drive side of the Neutral drive gate.
  10.  
  11. Tighten the nut.
  12.  

Turbo Hydra-Matic 350 and 400 Transmissions
1970-72 VEHICLES

See Figure 1



Click image to see an enlarged view

Fig. Fig. 1: Turbo Hydra-Matic shift linkage - 1970-72 vehicles

  1. The shift tube and levers located in the mast jacket of the steering column must move freely and must not bind.
  2.  
  3. Pull the shift lever toward the steering wheel and allow the lever to be positioned in Drive by the transmission detent. The pointer may be out of adjustment, so don't use the pointer on the column as a reference for positioning the lever. The pointer must be adjusted last.
  4.  
  5. Release the selector lever. The lever should not go into Low unless the lever is lifted.
  6.  
  7. Lift the lever toward the steering wheel and permit the lever to be placed in Neutral by the transmission detent.
  8.  
  9. Release the lever; it should not go into Reverse unless the lever is lifted.
  10.  
  11. If the linkage is adjusted correctly, the shift lever will not move past the Neutral detent and the Drive detent unless the lever is lifted so it can pass over the mechanical stop in the steering column.
  12.  
  13. If adjustment is necessary, place the lever in the Drive or High detent position. If the indicator pointer is out of alignment, you must rely upon the detent position to determine what gear you are in (see Steps 2 and 3).
  14.  
  15. Loosen the adjustment swivel or clamp at the cross-shaft and move the shift lever so that it contacts the drive stop in the column.
  16.  
  17. Tighten the swivel and recheck the adjustment (see Steps 2 and 6).
  18.  
  19. If the indicator pointer fails to line up properly with the gear symbol (P, R, N, D, L) or aligns with a wrong symbol (being in Reverse when the pointer indicates Neutral, etc.), the cause may be a bent indicator wire. Inspect it and repair.
  20.  
  21. If necessary, readjust the neutral safety switch to agree with the detent positions. The ignition key should move into LOCK only when the shift lever is in Park.
  22.  


WARNING
The above adjustments must be made correctly to prevent early transmission failure caused by controls not being fully engaged with the detent. This results in a situation in which fluid pressure is reduced causing only partial engagement of the clutches. It may appear to run well but the pressure reduction may be just enough to cause clutch failure after only a few miles of operation.

1973-79 VEHICLES

See Figure 2



Click image to see an enlarged view

Fig. Fig. 2: Turbo Hydra-Matic shift linkage - 1973-79 vehicles

  1. The shift tube and lever assembly must be free in the mast jacket.
  2.  
  3. Lift the selector lever toward the steering wheel and allow the selector lever to be positioned in Drive by the detent. Do not use the selector lever pointer as a reference.
  4.  
  5. Release the selector lever. The lever should not be able to go into Low unless the lever is lifted.
  6.  
  7. Lift the selector lever toward the steering wheel and allow the lever to be positioned in Neutral by the transmission detent.
  8.  
  9. Release the selector lever. The lever should not be able to engage Reverse unless the lever is lifted. A properly adjusted linkage will prevent the lever from moving beyond both the Neutral and Drive detents unless the lever is lifted.
  10.  
  11. If adjustment is required, remove the screw and spring washer from the swivel.
  12.  
  13. Set the transmission lever in Neutral by moving it counterclockwise to L and then three detents clockwise to Neutral.
  14.  
  15. Put the transmission selector lever in Neutral as determined by the mechanical stop in the steering column.
  16.  
  17. Do not use the pointer to determine these positions.
  18.  
  19. Assemble the swivel spring and washer to the lever and tighten to 20 ft. lbs. (27 Nm).
  20.  
  21. Readjust the neutral safety switch if necessary.
  22.  
  23. Check the operation. With the key in RUN , and the transmission in Reverse, be sure that the key cannot be removed and the steering wheel is not locked.
  24.  

With the key in LOCK and the shift lever in Park, be sure that the key can be removed, the steering wheel is locked, and that the transmission remains in Park when the steering column is locked.

Any inaccuracies in the above adjustments may result in premature transmission failure, due to operation of the transmission with the controls not in the full detent. Partial engagement of clutches and other internal parts will result in transmission failure after only a few miles.

THROTTLE VALVE LINKAGE



See Figure 3



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Fig. Fig. 3: Throttle valve adjustment - Powerglide transmissions

This procedure applies to Powerglide transmissions only.

6-Cylinder Engines
  1. With the accelerator depressed, the bellcrank on the engine must be in the wide open throttle position.
  2.  
  3. The dash lever must be 1 / 64 - 1 / 16 in. off the lever stop and the transmission lever must be against the transmission internal stop.
  4.  

V8 Engines
  1. Remove the air cleaner.
  2.  
  3. Disconnect the accelerator linkage at the carburetor.
  4.  
  5. Disconnect the accelerator return spring and throttle valve rod return springs.
  6.  
  7. Pull the throttle valve rod forward until the transmission is through the detent. Open the carburetor to the wide-open position. The carburetor must reach the wide open throttle position at the same time that the ball stud contacts the end of the slot in the upper throttle valve rod.
  8.  
  9. Adjust the swivel on the end of the upper throttle valve rod as per Step 4. The allowable tolerance is approximately 1 / 32 in.
  10.  
  11. Connect and adjust the accelerator linkage.
  12.  
  13. Check for freedom of operation. Install the air cleaner.
  14.  

THROTTLE VALVE (TV) CABLE



See Figure 4



Click image to see an enlarged view

Fig. Fig. 4: Turbo Hydra-Matic TV cable (self adjusting)

This applies to Turbo Hydra-Matic transmissions.

  1. With the engine stopped, move the slider back through the fitting in the direction away from the throttle body until the slider stops against the fitting.
  2.  
  3. Release the readjust tab.
  4.  
  5. Open the throttle lever to the "full throttle stop" position to automatically adjust the cable. release the lever.
  6.  

DETENT CABLE



This procedure applies to Turbo Hydra-Matic 350 transmissions.

1970-71 Models

See Figure 5



Click image to see an enlarged view

Fig. Fig. 5: Detent cable adjustment - 1970-72 vehicles

  1. Remove the air cleaner.
  2.  
  3. Loosen the detent cable screw.
  4.  
  5. With the choke off and the accelerator linkage adjusted, position the carburetor lever in the wide-open.
  6.  
  7. Pull the detent cable rearward until the wide open throttle stop in the transmission is felt. The cable must be pulled through the detent position to reach the wide open throttle stop in the transmission.
  8.  
  9. Tighten the detent cable screw and check the linkage for proper operation.
  10.  

1972 Models

See Figure 5

  1. Remove the air cleaner.
  2.  
  3. Pry up on each side of the snap-lock with a screwdriver to release the lock.
  4.  
  5. Compress the locking tabs and disconnect the locking tabs from the bracket.
  6.  
  7. Attach the snap-lock to the accelerator control lever and install the retaining ring.
  8.  
  9. Pull the carburetor to the wide open throttle position against the stop on the carburetor.
  10.  
  11. With the carburetor held in this position, pull the cable housing rearward until the wide open throttle stop in the transmission is felt.
  12.  
  13. Push the snap lock on the cable downward until it is flush with the cable.
  14.  
  15. Do not lubricate the cable. Install the air cleaner.
  16.  

1973-79 Models

See Figure 6



Click image to see an enlarged view

Fig. Fig. 6: Detent cable adjustment - 1973-79 vehicles

With the snap-lock disengaged from the bracket, position the carburetor at the wide open throttle position. Push the snap-lock downward until the top is flush with the rest of the cable.

DETENT SWITCH



This applies to Turbo Hydra-Matic 400 transmissions only.

1970-71 Models

See Figures 7 and 8



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Fig. Fig. 7: Detent switch adjustment - 1970 396 V8 engine



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Fig. Fig. 8: Detent switch adjustment - 1970-71 vehicles, except 396 V8 engine

Adjust the detent switch as shown in the accompanying illustrations.

1972-79 Models

See Figure 9



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Fig. Fig. 9: Detent switch adjustment - 1972-79 models

  1. Install the detent switch as shown.
  2.  
  3. After installing the switch, press the switch plunger as far forward as possible. This will preset the switch for adjustment. The switch will automatically adjust itself with the first wide open throttle application of the accelerator pedal.
  4.  

 
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