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How to install a BBK Underdrive Pulleys on your 1996-1999 Mustang

Installation Time

2 hours

American Muscle
Shop Parts in this Guide


1. Disconnect the battery.

2. Loosen alternator nut (this will require an air impact gun). Do not remove.

3. Loosen the four (4) bolts for the water pump pulley. Do not remove. On truck models, the engine fan is threaded onto the water pump shaft end-it must be unthreaded in a normal CCW direction using a large wrench on the hex-nut portion of the fan clutch where it meets the water pump pulley. Additionally you will need a tool which attaches across two (2) of the water pump pulley bolts and allows you to put resistance in the direction of the fan nut while breaking the nut free-otherwise the water pump will simply rotate while attempting this removal.

4. Remove center bolt and washer from the factory pulley/dampener.

5. Remove alternator pulley and water pump pulley.

6. Use a three (3) prong harmonic dampener puller to remove the factory pulley/balancer.


Hold the pulley with one hand when removing it. This will keep the pulley/dampener from falling to the ground when it clears the end of the crankshaft.

7. Install hub of factory harmonic balancer pulley in counter bore of new pulley. Align threaded hole in each pulley together. The keyway location is not important.

8. Install and hand tighten three (3) 1/4 x 1-1 /4" bolts. The factory pulley does not completely sit into the underdrive at this point. Carefully tighten the three (3) bolts equally in small increments to draw the two (2) pulleys together.

9. Remove the three (3) 1/4" bolts.

10. Apply a hi-temp silicon sealer to the two (2) pulley assembly keyway. Place pulley assembly onto the crankshaft. (Align pulley keyway with crankshaft key.)

11. Reinstall the three (3) 1/4" hex bolts using locktite #242 and tighten to 10-12 ft/lbs.

12. Align the keyway on the two (2) pulley assembly with the keyway on the crankshaft and slide it on to the crankshaft.


Place the two (2) pulley assembly in HOT water for about 15-20 minutes prior to installation

13. Attach the two (2) pulley assembly to the crankshaft using the new 12mm bolt provided and the original crank bolt washer.

14. Use locktite #242 or equivalent on the bolt and torque to 60 ft/lbs.

15. Install the new water pump pulley using the original hardware. Use locktite #242 or equivalent. On truck models, reverse Step 4 in order to reattach the fan.

16. Install the alternator pulley with the appropriate one of two supplied spacers to allow proper belt alignment and attach with original hardware.

17. Reinstall the belt. Consult a shop manual for proper procedure.


Inspect belt prior to reinstalling. If evidence of wear exists, replace it with a new belt.

18. Tighten alternator nut using an air impact gun.

19. Tighten water pump bolts evenly.

20. Reconnect battery.

21. Start engine and check belt for proper alignment.

Identification Guide for 4.6L Water Pump Pulleys

Visually identify which water pump pulley you have before installing regardless of model year. The early water pump pulley had a convex or ''bowed-out'' face and the pulley on the later water pump has a concave or ''pressed-in face''. There is no exact changeover date for the pump and pulley. Supposedly the water pump changeover occurred in January of 2000, but we have seen cars with identical January build dates and different water pumps and pulleys. We have also seen the early design pulleys used on a few 2002 models,

Refer to the pictures below to determine which pulley design you have. Since there is no definitive answer as to the time line or model years.

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