Differential Service

This procedure covers draining, cleaning, and refilling the front and rear differentials on a 2007 Ram 3500 4WD with fresh 75W-90 synthetic gear oil.

Warnings

Tools required

Parts

• Front differential cover gasket × 1 — Use OEM Mopar or equivalent
• Rear differential cover gasket × 1 — Use OEM Mopar or equivalent
• Front differential drain plug washer (if equipped) × 1 — Use OEM specification
• Rear differential drain plug washer (if equipped) × 1 — Use OEM specification
• RTV silicone gasket maker (if not using pre-cut gaskets) × 1 — Permatex Ultra Grey or equivalent

Fluids

• 75W-90 synthetic gear oil (front differential) — 3.5 qt
• 75W-90 synthetic gear oil (rear differential) — 5.5 qt

Preparation

1. Park vehicle on level ground and apply parking brake
2. Place wheel chocks behind front wheels
3. Raise rear of vehicle and support securely on jack stands at frame or axle
4. Allow differential to cool if vehicle was recently driven
5. Verify you have correct 75W-90 synthetic gear oil (do not use standard gear oil)
6. Have drain pan, new gaskets, and RTV sealant ready before starting

Procedure

1. 1

   Drain rear differential
   Position drain pan under rear differential. If equipped with a drain plug, remove drain plug and allow fluid to drain completely. If no drain plug is present, carefully loosen all cover bolts in a crisscross pattern, then remove lower bolts first to allow fluid to drain while keeping cover partially attached. Once drained, remove remaining bolts and cover.
2. 2

   Clean rear differential cover and housing
   Remove old gasket material from both the differential cover and housing mating surface using a gasket scraper. Be careful not to gouge the cast iron/steel mating surfaces. Use wire brush to clean bolt threads. Wipe surfaces clean with shop rags. Inspect inside housing for metal shavings or debris - a small amount of fine metal dust on the magnet is normal, but large chunks indicate wear issues.
3. 3

   Install rear differential cover
   Install new gasket on differential cover, or apply a 1/8-inch bead of RTV silicone around the cover perimeter if using RTV method. Position cover onto housing and install all bolts hand-tight. Torque cover bolts in a crisscross pattern to manufacturer specification (approximately 30 ft-lbs for AAM axles, but verify exact value in factory service manual for your specific rear axle model). Allow RTV to cure for 15 minutes before filling if used.
4. 4

   Refill rear differential
   Locate fill plug on front or side of differential housing (passenger side on most models). Remove fill plug. Using fluid transfer pump or squeeze bottle, add 75W-90 synthetic gear oil through fill hole until oil begins to drip from fill hole. This indicates proper fill level. Install fill plug and torque to specification.
5. 5

   Drain front differential
   Move drain pan under front differential. Remove drain plug if equipped, or remove cover bolts in crisscross pattern starting with lower bolts to allow controlled draining. On the AAM 9.25 front differential used in this application, cover removal is typical as it has a removable cover. Verify axle model in service documentation before beginning. Allow all fluid to drain completely.
6. 6

   Clean front differential cover and housing
   Scrape all old gasket material from cover and housing mating surfaces. Clean bolt threads with wire brush. Inspect differential housing interior for excessive metal debris on magnetic drain plug or bottom of housing. Wipe all surfaces clean with shop rags.
7. 7

   Install front differential cover
   Position new gasket on front differential cover or apply RTV silicone bead as done with rear. Install cover and hand-tighten all bolts. Torque bolts in crisscross pattern to manufacturer specification (approximately 30 ft-lbs for AAM 9.25 axle, verify in factory service manual). If using RTV, allow 15-minute cure time before filling.
8. 8

   Refill front differential
   Remove fill plug from front differential housing (usually located on driver side or front face of housing). Using fluid pump, add 75W-90 synthetic gear oil through fill hole until oil reaches bottom of fill hole and begins to seep out (AAM 9.25 front axle capacity is approximately 1.5-1.75 quarts — verify in factory service manual). Install and torque fill plug.
9. 9

   Check for leaks and lower vehicle
   Wipe all drain plugs, fill plugs, and cover areas clean with shop rag. Inspect for any immediate leaks around gaskets or plugs. Lower vehicle from jack stands back to ground. Remove wheel chocks.

Reassembly

1. Ensure all differential cover bolts are torqued to specification in proper sequence
2. Verify both fill plugs are installed and tight
3. Double-check that drain plugs are installed if your axles have them

Verification

• Start engine and drive vehicle forward and reverse several feet to circulate new gear oil
• Re-check all differential covers, drain plugs, and fill plugs for leaks after test drive
• Inspect under vehicle after 50-100 miles of driving to verify no seepage from gaskets
• Monitor for unusual noises from differentials during normal driving - properly serviced differentials should operate quietly

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