Only the THM250 has an externally adjustable band. Band adjustments are not externally possible on other transmissions. The intermediate band must be adjusted with every required fluid change or whenever there is slippage.
- Position the shift lever in Neutral.
- Loosen the locknut on the right side of the transmission. Tighten the adjusting screw to 30 inch lbs. (3 Nm)
- Back the screw out three turns and then tighten the locknut to 15 ft. lbs. (20 Nm)
- Place the shift lever in Neutral.
- Loosen the shift rod clamp screw and make sure the lever on the transmission is in the Neutral position. If you are unsure as to which position is Neutral, have someone move the shift lever through the gears while you watch the lever on the transmission.
- With the lever on the transmission in the Neutral position and the shift lever on the column being held against the Neutral stop (do not raise the lever), tighten the shift rod clamp screw to 23 ft. lbs. (31 Nm)
- Check the operation of the shifter.
- Place the shift lever in the Park position.
- The ignition key must be in the LOCK position.
- Make sure the lever on the transmission is in the Park position.
- Loosen the shift rod clamp screw.
- Loosen the pin in the lever on the transmission.
- Pull the shift rod lightly against the lock stop at the shifter and tighten the clamp screw.
- Adjust the pin at the transmission lever for a "free pin" fit, and tighten the attaching nut.
- Check the operation of the shifter.
THROTTLE VALVE (TV) OR DETENT CABLE
See Figures 1, 2 and 3
On all transmissions except the THM250, THM350 and THM400 models, a TV cable is used to control hydraulic pressures, shift points, shift feel, and downshifting. The THM250 and THM350 use a detent cable.
THM400 models use an electrical detent (downshift) switch. Adjustment of this switch is covered separately.
Though the detent cable is virtually identical in appearance to the TV cable, the detent cable controls only the downshift function of the cable.
Before attempting adjustment, identify the style of the cable which is used in your vehicle (Type One or Type Two). The Type One Cable uses a snap lock assembly which is integral with the cable. The snap lock is located next to the cable mounting bracket at the engine. In its normal position, the snap lock is pushed fully downward (locked) so that it is flush with the snap lock assembly. Adjustment is made with the snap lock in the raised (unlocked) position, as outlined in the Type One adjustment procedure.
The Type Two cable uses a different type of locking mechanism. Though it is located in the same position as the Type One snap lock, the Type Two lock tab is set when released (upward) and adjusted when pushed downward (unlocked). On 1981 and earlier models, the Type Two cable can be easily identified by the presence of a spring, visible beneath the lock tab. The spring is not exposed on 1982 and later cable assemblies. Refer to the Type Two adjusting procedure to adjust this type of cable.
- Remove the engine air cleaner assembly.
- Push up on the bottom of the snap lock at the cable bracket. Make sure that the cable is free to slide through the snap lock.
- Move the carburetor lever to the wide open throttle position and hold it there.
- Push the snap lock flush and let the lever return to the closed position.
- If the adjustment does not correct late shifting or no part throttle downshift, a transmission fluid pressure test should be made by a qualified mechanic.
- Depress and hold the metal lock tab on the TV cable.
- Move the slider back through the fitting in the direction away from the throttle body until the slider stops against fitting.
- Release the metal lock tab.
- Open the throttle lever to full throttle stop position. This will automatically adjust the slider on the cable to the correct setting.
See Figure 4
Turbo Hydra-Matic 400 transmissions are equipped with an electrical detent, or downshift switch operated by the throttle linkage.
- Pull the detent switch driver rearward until the hole in the switch body aligns with the hole in the driver. Insert a 0.090 in. diameter pin through the aligned holes to hold the driver in position.
- Loosen the switch plunger as far forward as possible. This will preset the switch for adjustment, which will occur on the first application of wide open throttle.