GM Firebird 1967-1981 Repair Guide

Automatic Transmission

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LEVEL CHECK



See Figures 1 through 5

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Fig. Fig. 1: With the engine hot, idling and the car parked on a level surface, remove the ATF level dipstick ...



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Fig. Fig. 2: ... and check the level of the ATF it should fall within the cross-hatched area (arrow)



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Fig. Fig. 3: If needed, add ATF through the dipstick tube check the level often while filling



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Fig. Fig. 4: If debris (arrows) is evident in your ATF pan, have the transmission checked by a technician



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Fig. Fig. 5: Depending on whether the transmission is cold, warm or hot, the fluid level may vary considerably

Check the automatic transmission fluid level at least every 6,000 miles (7,500 miles for 1975 and later models). The dipstick can be found in the rear of the engine compartment. The fluid level should be checked only when the transmission is hot (normal operating temperature). The transmission is considered hot after about 20 miles of highway driving.

  1. Park the car on a level surface with the engine idling. Shift the transmission into Neutral and set the parking brake.
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  3. Remove the dipstick, wipe it clean and reinsert it firmly. Be sure that it has been pushed all the way in. Remove the dipstick again and check the fluid level while holding it horizontally. With the engine running, the fluid level should be between the second notch and the "FULL HOT" line. If the fluid must be checked when it is cool, the level should be between the first and second notches.
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  5. If the fluid level is below the second notch (engine hot) or the first notch (engine cold), add DEXRONreg; (1967-75) or DEXRONreg; II (1976 and later) automatic transmission fluid through the dipstick tube. This is easily done with the aid of a funnel. Check the level often as you are filling the transmission. Be extremely careful not to overfill it. Overfilling will cause slippage, seal damage and overheating. Approximately one pint of ATF will raise the fluid level from one notch/line to the other.
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Always use DEXRONreg; or DEXRONreg; II ATF. The use of ATF Type F or any other fluid will cause severe damage to the transmission.

The fluid on the dipstick should always be a bright red color. If it is discolored (brown or black), or smells burnt, serious transmission troubles, probably due to overheating, should be suspected. The transmission should be inspected by a qualified technician to locate the cause of the burnt fluid.

FLUID & FILTER CHANGE



See Figures 6 through 18

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Fig. Fig. 6: The transmission gasket shape, as with this Powerglide gasket, can be used for transmission model identification



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Fig. Fig. 7: Transmission gasket shape for the Turbo Hydra-Matic (THM) 200 model



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Fig. Fig. 8: Transmission gasket shape for the THM 250, 350 and 375 models



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Fig. Fig. 9: Transmission gasket shape for the THM 400, the strongest automatic transmission made by GM for 1967-81 vehicles



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Fig. Fig. 10: When installing the filter assembly on THM 400 transmissions, make certain to install a new O-ring on the intake pipe



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Fig. Fig. 11: Raise and support the vehicle safely, then remove the ATF pan side bolts ...



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Fig. Fig. 12: ... position the shift linkage aside ...



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Fig. Fig. 13: ... remove the front bolts, loosen the rear bolts and carefully pry the pan down to drain the fluid



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Fig. Fig. 14: Remove the rear bolts and lower the pan completely to drain the rest of the fluid



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Fig. Fig. 15: Once the pan is removed, access to the filter (arrow) is gained



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Fig. Fig. 16: Remove the 2 filter mounting bolts ...



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Fig. Fig. 17: ... then pull the filter down and off of the transmission valve body



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Fig. Fig. 18: Before installing the new filter, make sure to remove the old filter gasket

A transmission fluid pan gasket should be included with the transmission fluid filter; it not, a new gasket must be purchased separately.

The fluid should be changed with the transmission warm. A 20 minute drive at highway speeds should accomplish this.

  1. Raise and support the vehicle, preferably in a level attitude.
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  3. With Turbo Hydra-Matic 250 or 350, support the transmission and remove the support crossmember.
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  5. Place a large pan under the transmission pan. Remove all the front and side pan bolts. Loosen the rear bolts about four turns.
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  7. Pry the pan loose and let the transmission fluid drain.
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  9. Remove the pan and gasket. Clean the pan thoroughly with solvent and allow it to air dry. Be very careful not to get any lint from rags in the pan.
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  11. Remove the strainer-to-valve body screws, the strainer, and the gasket. Most 350 transmissions will have a throw-away filter instead of a strainer. On the 400 transmission, remove the filter retaining bolt, filter, and intake pipe O-ring.
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  13. If there is a strainer, clean it in solvent and allow it to air dry.
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  15. Install the new filter or cleaned strainer with a new gasket. Tighten the screws to 12 ft. lbs. On the 400, install a new intake pipe O-ring and a new filter, tightening the retaining bolt to 10 ft. lbs.
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  17. Install the pan with a new gasket. Tighten the bolts evenly to 12 ft. lbs. (8 ft. lbs. for Powerglide and Torque Drive transmissions).
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  19. Lower the car and add the proper amount of DEXRONreg; or DEXRONreg; II automatic transmission fluid through the dipstick tube.
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  21. Start the engine in Park and let it idle. Do not race the engine. Shift into each shift lever position, shift back into Park, and check the fluid level on the dipstick. The level should be 1 / 4 in. below ADD. Be very careful not to overfill. Recheck the level after the car has been driven long enough to thoroughly warm up the transmission. Add fluid as necessary. The level should then be at FULL.
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