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How to install a BBK Underdrive Pulleys on your Mustang on your Mustang

Installation Time

2 hours


The BBK Street Pulley Kit is designed to increase power by reducing the overall speed of the serpentine system, and should in no way create a charging or cooling problem. However, an examination of the fan clutch, thermostat, and radiator should be performed to insure proper operation. (Cars equipped with high drawing aftermarket sound systems should check charging effectiveness before installation of underdrive pulleys.)

Step 1 Loosen alternator nut, water pump and crank pulley bolts while belt is still in tension. (To simplify removal of the alternator pulley loosen with an air impact, with belt in place.)

Step 2 Remove belt.

Step 3 Bolts and three factory pulleys can now be easily removed.

Step 4 Install new pulleys with bolts hand tight at this point. Install belt. Torque all bolting per factory specifications.

(Use of Loctite thread lock is recommended on all threads.)

NOTE A strap wrench or impact driver may be required to properly torque alternator nut

Step 5 Check that belt is properly seated in all pulleys. Insure tensioner arrow is within the indicator marks on tensioner. If adjustment is required, relax tensioner from belt, loosen upper 9/16 hex alternator anchor bolt, shift alternator toward air cleaner or allow it to move in as required within the clearance of the diameters. Tighten while holding alternator. If additional adjustment is required, remove belt, loosen 3/4” nut while holding tensioner pulley.

Step 6 Set warm idle speed for automatic cars at 650-700 rpm in drive. Standard shift at 750-800 rpm.