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How to Install Underdrive Pulleys for a 1996-2004 Mustang GT and Cobra

Installation Time

2 hours

Tools Required
  • 3/8" Drive Ratchet with 10mm, 11mm, 18mm, and 15/16" Socket
  • Breaker Bar
  • Torque Wrench (capable of at least 60 ft-lb.)
  • Air Impact Gun (for alternator pulley)
  • Harmonic Balancer Puller
  • High Temp RTV Silicone
American Muscle
Shop Parts in this Guide


1. Disconnect battery before starting installation. Loosen alternator pulley with an impact gun and 15/16” socket. Loosen water pump pulley with a ratchet and 10mm socket.

2. Loosen crankshaft balancer by using a 1/2” drive breaker bar and an 18mm socket.Tip:For manual transmission cars, place car in gear before loosening crank bolt. For automatic transmission cars, remove transmission inspection cover and wedge a wrench in between the flywheel and bell housing to prevent the engine from turning over.

3. Remove accessory drive belt by using a 3/8” drive ratchet and releasing belt tension with the tensioner.

4. Once the belt is removed, you can finish removing the alternator and water pump pulleys. Remove the crank pulley bolt and washer. Without the washer, thread the factory crank bolt about halfway back in and use a harmonic balancer puller to remove the factory balancer.

5. Place factory balancer over Stack Racing crank pulley. Using supplied 11mm bolts and washers, join the factory balancer and Stack pulley as shown. Tighten three bolts in small increments to carefully draw the two pulleys together. When pulleys are fully seated, back bolts off a full turn and tighten with a torque wrench to 12 ft-lb. If you are having trouble trying to seat the pulleys, placing them in hot water for 10-15 Mins prior to installation.

6. Place high-temp RTV silicone into keyway on pulley assembly and slide onto crankshaft snout as shown. Install new supplied crankshaft bolt with factory washer and tighten to 60 ft-lb. using a torque wrench.

7. Using factory nut, install new alternator pulley with an impact gun. Using factory hardware, install new water pump pulley with a ratchet and 10mm wrench.

8. Re-install accessory drive belt and re-connect battery to complete installation. When restarting vehicle, make sure the pulleys are properly aligned and there are no unusual sounds before taking the car for a drive.

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