Reduction Gear Service

This procedure covers the removal, inspection, and replacement of the reduction gear assembly in the dual motor AWD electric drivetrain of the 2025 Rivian EDV 500.

Warnings

Tools required

Parts

• Reduction gear assembly gasket/seal kit × 1 — Use OEM specification
• Drain plug crush washer (per motor) × 2 — Use OEM specification
• Fill plug O-ring (per motor) × 2 — Use OEM specification
• Output shaft seal (per motor) × 2 — Use OEM specification
• Reduction gear assembly (if replacement required) × 1 — Use OEM specification

Fluids

• EV Transmission Fluid — 10 qt
• EV Battery/Motor Coolant — 2 qt

Preparation

1. Park vehicle on level surface and engage parking brake
2. Connect Rivian diagnostic scan tool and perform high voltage system shutdown procedure
3. Disconnect 12V auxiliary battery negative terminal
4. Verify high voltage system is disabled using diagnostic tool and multimeter - confirm 0V across HV bus
5. Raise vehicle on lift to working height and secure with safety locks
6. Remove all four wheels and set aside
7. Remove underbody protective panels to access motor assemblies
8. Place warning tags on HV disconnect location indicating service in progress
9. Allow motors and reduction gear assemblies to cool completely if vehicle was recently operated

Procedure

1. 1

   Drain reduction gear fluid from both motors
   Position drain pan under front motor reduction gear housing. Remove drain plug from bottom of reduction gear housing and allow fluid to drain completely (approximately 1.5 quarts). Inspect drained fluid for metal particles or debris. Repeat process for rear motor reduction gear housing (approximately 2 quarts). Remove fill plugs from both housings to ensure complete drainage.
2. 2

   Disconnect motor coolant lines
   Identify coolant lines connected to motor cooling jackets. Clamp off coolant lines using appropriate hose clamps to minimize fluid loss. Disconnect coolant quick-connect fittings at both front and rear motors. Cap or plug open lines immediately to prevent contamination. Expect approximately 2 quarts of coolant drainage.
3. 3

   Disconnect electrical connections from motors
   Document all electrical connector orientations with photos. Disconnect high voltage phase connectors from both front and rear motors - verify connectors are properly locked out. Disconnect temperature sensors, resolver/encoder connectors, and any auxiliary sensor connections. Secure all disconnected harnesses away from work area.
4. 4

   Remove drive axle connections
   Remove axle retaining hardware at CV joint connections to both front and rear reduction gear output shafts. Support drive axles with wire or axle support to prevent damage to CV joints and boots. Mark axle orientation for reassembly. Separate axles from reduction gear output flanges.
5. 5

   Support motor and reduction gear assembly
   Position electric motor support fixture under the motor assembly requiring service (front or rear based on service needs). Adjust fixture to properly support motor weight. Remove motor mount bolts securing motor/reduction gear assembly to subframe. Verify all electrical, coolant, and mechanical connections are disconnected before proceeding.
6. 6

   Remove motor/reduction gear assembly from vehicle
   Carefully lower motor and reduction gear assembly using support fixture. Guide assembly clear of subframe, suspension components, and body panels. Remove assembly from under vehicle and place on clean workbench. Repeat for second motor if servicing both front and rear assemblies.
7. 7

   Separate reduction gear from motor housing
   With motor assembly on workbench, remove bolts securing reduction gear housing to motor housing. Carefully separate reduction gear assembly from motor, noting alignment dowel positions. Remove and inspect housing gasket/seal - discard and prepare new seal for installation.
8. 8

   Disassemble and inspect reduction gear components
   Remove reduction gear cover bolts and carefully separate cover from housing. Document gear mesh pattern and gear positions with photos. Remove output shaft assembly, gears, bearings, and shims in order, keeping all components organized. Inspect all gears for wear, pitting, or scoring. Check all bearings for roughness, noise, or excessive play. Measure gear backlash with dial indicator and record measurements. Inspect housing for cracks or damage.
9. 9

   Clean and prepare components for reassembly
   Thoroughly clean all reduction gear components with appropriate solvent. Dry components with compressed air and lint-free cloths. Inspect housing mating surfaces and ensure they are clean and free of old gasket material. Check all threaded holes for damage and clean with appropriate tap if needed. Prepare new seals, gaskets, and O-rings for installation.
10. 10

    Reassemble reduction gear with new or serviced components
    Install bearings onto gear shafts using appropriate bearing drivers. Install gears into housing with original shims (or adjusted shims if replacing components). Apply thin coat of EV transmission fluid to all moving parts during assembly. Install output shaft assembly with new output shaft seal. Verify gear alignment and backlash matches specifications recorded during disassembly or factory specifications if installing new reduction gear assembly.
11. 11

    Install reduction gear cover and verify operation
    Install new gasket on reduction gear housing mating surface. Carefully position cover onto housing, aligning dowel pins. Install and hand-tighten all cover bolts in star pattern. Since no torque specifications are available in database, follow manufacturer service manual for proper torque values. Rotate output shaft by hand to verify smooth operation with no binding or unusual noise.
12. 12

    Reinstall reduction gear assembly to motor housing
    Install new gasket/seal between motor housing and reduction gear housing. Align reduction gear assembly to motor housing using alignment dowels. Install mounting bolts and tighten in star pattern per manufacturer specifications. Verify motor rotor rotates freely without interference.
13. 13

    Reinstall motor/reduction gear assembly into vehicle
    Position motor support fixture under assembled motor/reduction gear unit. Raise assembly into position on subframe, carefully guiding around suspension and body components. Align motor mounts to subframe mounting points. Install motor mount bolts and tighten per manufacturer specifications. Remove support fixture once motor is secured.
14. 14

    Reconnect drive axles and electrical connections
    Reconnect drive axles to reduction gear output flanges, aligning marks made during disassembly. Install axle retaining hardware and tighten per specifications. Reconnect all electrical connectors to motors including high voltage phase connectors, temperature sensors, and resolver/encoder connections. Verify all connectors are fully seated and locked.
15. 15

    Reconnect coolant lines and refill fluids
    Reconnect motor coolant quick-connect fittings at both motors. Remove hose clamps. Fill reduction gear housings with specified EV transmission fluid through fill ports (1.5 quarts front, 2.0 quarts rear). Install new fill plug O-rings and install fill plugs. Install drain plugs with new crush washers. Top off motor coolant system and bleed air from cooling system per manufacturer procedure.

Reassembly

1. Reinstall underbody protective panels and torque fasteners per manufacturer specifications
2. Reinstall all four wheels and torque lug nuts to specification
3. Reconnect 12V auxiliary battery negative terminal
4. Remove warning tags from HV disconnect location
5. Using Rivian diagnostic tool, reactivate high voltage system following manufacturer procedure
6. Verify no diagnostic trouble codes are present related to motor or reduction gear systems
7. Check for fluid leaks around reduction gear housings, drain plugs, and coolant connections

Verification

• With vehicle on lift, start vehicle and engage drive mode - listen for unusual noises from reduction gear assemblies
• Perform low-speed test drive and verify smooth operation in both forward and reverse
• Test acceleration and regenerative braking - confirm no vibration, noise, or fault messages
• Monitor motor and reduction gear temperatures using diagnostic tool during test drive
• Recheck fluid levels after test drive and top off if necessary
• Perform final inspection for leaks around all service points
• Clear any service mode indicators using diagnostic tool and verify all systems operational

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