Transmission Pan Gasket

This procedure covers removal and replacement of the 6L80/6L90 automatic transmission pan gasket, including fluid drain, pan cleaning, and refill with new ATF.

Warnings

Tools required

Parts

• Transmission pan gasket × 1 — ACDelco 24278868 or equivalent
• Transmission filter (if equipped with replaceable filter) × 1 — ACDelco 24278882 or equivalent

Fluids

• ACDelco Dexron VI ATF — 11.5 qt

Preparation

1. Park vehicle on level surface and engage parking brake
2. Allow transmission to cool if recently driven
3. Raise and safely support vehicle on jack stands at all four corners to ensure level position
4. Verify you have adequate Dexron VI ATF on hand (at least 6 quarts for refill)
5. Locate transmission pan at bottom rear of transmission case

Procedure

1. 1

   Position drain pan and loosen pan bolts
   Position a large drain pan (12+ quart capacity) beneath the transmission pan. Begin loosening all transmission pan bolts approximately 2-3 turns each, working in a criss-cross pattern to prevent warping the pan. Leave bolts in place at this stage.
2. 2

   Break pan seal and drain fluid
   Carefully loosen one corner of the pan bolts further to break the seal and allow fluid to begin draining. Control the drainage by adjusting how far the bolts are loosened. Once flow slows, remove all pan bolts except two at opposite corners to keep pan controlled.
   ⚠Fluid will drain forcefully when seal is broken. Keep hands clear and reposition drain pan as needed.
3. 3

   Remove transmission pan
   Remove the final two pan bolts and carefully lower the transmission pan. Tilt one edge down to pour remaining fluid into drain pan. Set pan aside for cleaning.
4. 4

   Inspect and remove transmission filter (if applicable)
   Inspect the transmission filter assembly. The 6L80/6L90 uses an internal filter that is typically accessible from the pan opening. If filter is serviceable from this access point, remove retaining bolts and pull filter straight down. Some model years may have a non-serviceable internal filter; consult service information if uncertain.
   Torque spec

   Sensor Bolts14 Nm (10 lb-ft)
5. 5

   Clean gasket surfaces
   Use a plastic or composite scraper to carefully remove all old gasket material from both the transmission case mating surface and the pan itself. Avoid using metal scrapers that could gouge the aluminum surfaces. Clean both surfaces thoroughly with brake cleaner and wipe dry with clean shop towels. Inspect for any damage or warping.
   ⚠Do not allow any debris or gasket material to fall into the open transmission case. Stuff a clean rag into the opening if needed during cleaning.
6. 6

   Clean transmission pan and magnet
   Thoroughly clean the inside of the transmission pan, paying special attention to the magnetic drain plug or magnet strips. Inspect debris on magnet for excessive metal particles (small amount of fine metallic dust is normal; large chunks or excessive material may indicate internal wear). Clean pan with solvent and dry completely.
7. 7

   Install new filter
   If transmission filter was removed, install new filter assembly with new seal/O-ring. Push filter fully into position and secure with retaining bolts. Ensure filter is properly seated before tightening.
   Torque spec

   Sensor Bolts14 Nm (10 lb-ft)
8. 8

   Install new gasket and position pan
   Position the new transmission pan gasket on the pan (some gaskets have adhesive backing, others may require gasket sealant per manufacturer instructions). Carefully lift the pan into position, aligning all bolt holes. Start all pan bolts by hand to ensure proper alignment.
9. 9

   Torque transmission pan bolts
   Torque all transmission pan bolts to specification in a criss-cross pattern, working from the center outward. Make multiple passes, gradually bringing bolts to final torque to ensure even gasket compression and prevent leaks.
   Torque spec

   Pan Bolts20 Nm (15 lb-ft)
10. 10

    Refill transmission with ATF
    Locate the transmission fill plug on the passenger side of the transmission case (requires removal of fill plug). Using a fluid transfer pump or funnel with flexible hose inserted into fill hole, add approximately 5-6 quarts of Dexron VI ATF. Do not overfill at this stage; exact level will be verified in next steps.
11. 11

    Lower vehicle and initial startup
    Lower vehicle from jack stands. Start engine and allow to idle. Shift transmission through all gear ranges (P-R-N-D-L) while holding brake, pausing 2-3 seconds in each position. Return to Park.
12. 12

    Check and set fluid level
    With engine running at idle and transmission in Park, raise vehicle again. Remove fill plug. Transmission fluid should be at operating temperature (160-200°F). Fluid level is correct when fluid just begins to drip from fill hole at operating temperature. Add or remove fluid as needed through fill hole, then reinstall fill plug.
    ⚠Transmission fluid will be hot. Use caution when removing fill plug and checking level.
    Torque spec

    Fill Plug42 Nm (31 lb-ft)

Reassembly

1. Verify all pan bolts are torqued to specification in criss-cross pattern
2. Ensure fill plug is reinstalled and torqued properly
3. Wipe down transmission case and pan exterior to identify any new leaks during test drive

Verification

• Start engine and verify no leaks from transmission pan area while idling
• Test drive vehicle through all gears, verifying smooth shifts with no slipping or harsh engagement
• Recheck fluid level at operating temperature and verify proper level at fill plug
• After test drive, inspect pan gasket area for any signs of seepage or leaks
• Check fluid level again after 50-100 miles of driving to ensure stability

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