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How to install a IRS Differential Cover on your 1999-2004 Mustang

Installation Time

2 hours

American Muscle
Shop Parts in this Guide


1. Prepare the housing for cover installation by cleaning the gasket surface and all cover mounting bolt holes.

2. Inspect the bearing caps and gears for excessive wear or cracks, replace if necessary.

3. If Installing LPW main cap stud kit, torque part # 321-4 (7/16”) to 65ft/lbs. Torque part # 325-4 (1/2”) to 85ft/lbs.

4. Remove the load bolt locking nuts and adjust the load bolts so they will not contact the bearing caps during cover installation.

Note: Adjust the swivel feet until they pivot freely on the load bolts before cover installation.

5. Apply silicone gasket sealant to the cover gasket surface. Also apply a small amount to the load bolt threads at the locking nut area to provide a positive seal once the load bolt is adjusted and locking nut installed.

Install support cover with all the cover mounting bolts finger tight.

6. Torque the cover mounting bolts. Applications with 5/16” bolts torque to 25ft/lbs. Applications with 3/8” bolts torque to 35 ft/lbs.

7. Torque the load bolts to 10ft/lbs.

Note: Do not exceed 10ft/lbs of torque or bearing distortion and component failure will occur.

8. Install and torque the load bolt locking nuts to 10ft/lbs.

Note: Do not over torque the load bolt locking nuts.

9. Add fluid to the manufacture’s recommended level. If your application has a factory fill plug on the side or front of the housing, it is the correct level to use.

Note: The fill plug on most LPW covers is located higher than the recommended level. Most LPW support covers increase fluid volume approximately one pint.

Applications w/o housing fill plug: Chrysler 8.2 & 8.3, 5 pints / Chrysler 9.25, 5-1/2 pints / Dana 30, 2-1/2 pints / Dana 35, 3-1/2 pints / Dana 44, 4-1/2 pints / Dana 60, 6-1/2 pints / Dana 70, 7-1/2 pints / Dana 80, 10 pints

Note: User and/or installer must make certain the LPW cover will not come in contact with and/or interfere with any suspension and/or chassis component. Do not attach any item(s) other than the LPW axle-tube brace to the ULTIMATE cover. Do not attach any item(s) to the ULTRA cover.

This guide applies to Vehicle years: 1999, 2001, 2003, 2004 and Submodels: Cobra