Differential Service

Drain, inspect, and refill the rear differential with fresh synthetic gear oil, replacing the drain and fill plug washers.

Warnings

Tools required

Parts

• Drain plug washer (copper or aluminum) × 1 — Use OEM specification
• Fill plug washer (copper or aluminum) × 1 — Use OEM specification

Fluids

• 75W-140 synthetic gear oil — 1.8 qt

Preparation

1. Park vehicle on level surface and engage parking brake.
2. If vehicle has been driven, allow differential to cool for at least 30 minutes.
3. Raise vehicle securely on lift or jack stands at all four corners to ensure level position.
4. Place wheel chocks at front wheels for additional safety.
5. Position drain pan beneath rear differential.

Procedure

1. 1

   Locate Differential Plugs
   Access the underside of the vehicle and locate the rear differential housing. Identify the fill plug on the side or front face of the differential housing (typically at the fill line level) and the drain plug at the bottom of the housing. Clean the area around both plugs with a wire brush to remove debris and prevent contamination during service.
2. 2

   Remove Fill Plug First
   Using the appropriate socket, loosen and remove the fill plug completely. This ensures you will be able to refill the differential after draining. If the fill plug is seized or will not turn, stop and address this issue before proceeding with draining. Inspect the fill plug washer for damage or deformation.
3. 3

   Drain Differential Fluid
   Position the drain pan directly beneath the drain plug. Using the appropriate socket, slowly loosen the drain plug. Once loose, carefully remove it by hand, allowing fluid to drain completely. This may take 5-10 minutes. While draining, inspect the old fluid for metal particles, water contamination, or unusual discoloration which may indicate internal wear or seal failure.
4. 4

   Inspect Drain Plug and Housing
   Once fluid has fully drained, inspect the drain plug for magnetic particles (normal light gray paste is acceptable; large metal chunks indicate excessive wear). Clean the drain plug threads with a shop rag. Inspect the drain hole threads in the differential housing for damage or cross-threading. If threads are damaged, they must be repaired before reassembly.
5. 5

   Install Drain Plug with New Washer
   Install a new drain plug washer onto the drain plug. Insert the drain plug into the housing and thread it in by hand to ensure proper thread engagement. Once hand-tight, torque the drain plug to the OEM-specified value (verify against Aston Martin service data) using a torque wrench. Note: Once hand-tight, torque the drain plug to the Aston Martin-specified value (verify exact torque against official 2009 DB9 service documentation) using a torque wrench.
   Torque spec

   Drain Plug55 Nm (41 lb-ft)
6. 6

   Refill Differential
   Using a fluid transfer pump or syringe with tubing, insert the fill tube into the fill plug hole. Slowly pump the Aston Martin-specified final drive/transaxle fluid (grade and specification per official 2009 DB9 service documentation — verify LSD/friction-modifier requirements) into the unit until oil begins to seep from the fill hole. Fill to the capacity specified by Aston Martin. The correct fill level is reached when oil is level with the bottom of the fill hole threads. Allow a few moments for oil to settle, then top off if necessary. Note: Slowly pump the Aston Martin-specified final drive gear oil into the differential until oil begins to seep from the fill hole. Confirm the exact grade and fill capacity against the official Aston Martin DB9 service documentation before filling. Note: Slowly pump fresh OEM-specified synthetic gear oil (verify grade and capacity against Aston Martin service data) into the differential until oil begins to seep from the fill hole.
7. 7

   Install Fill Plug with New Washer
   Install a new fill plug washer onto the fill plug. Wipe any excess oil from around the fill hole opening. Insert the fill plug and thread it in by hand until snug, then torque to the OEM-specified value (verify against Aston Martin service data) using a torque wrench. Note: Insert the fill plug and thread it in by hand until snug, then torque to the Aston Martin-specified value (verify exact torque against official 2009 DB9 service documentation) using a torque wrench.
   Torque spec

   Fill Plug55 Nm (41 lb-ft)
8. 8

   Clean and Inspect for Leaks
   Wipe down the differential housing and surrounding area to remove any spilled oil. Lower the vehicle to the ground. Wipe down the differential housing and surrounding area to remove any spilled oil, then raise the vehicle again and inspect both drain and fill plugs for any signs of leakage. After confirming no leaks, the differential service is complete. Note: Lower the vehicle to the ground. With the parking brake engaged and wheels chocked, inspect the surrounding area, then raise the vehicle again and inspect both drain and fill plugs for any signs of leakage.

Reassembly

1. No disassembly was required beyond plug removal; vehicle is ready for service verification.
2. Dispose of used differential fluid according to local environmental regulations.

Verification

• Confirm both drain and fill plugs are torqued to specification and show no signs of leakage.
• Take a short test drive (5-10 minutes) including both acceleration and deceleration to circulate new fluid.
• After test drive, re-inspect plugs for any seepage or leaks.
• Normal operation should result in smooth power delivery without whining, grinding, or vibration from the rear differential.

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