How to Install an Underdrive Pulley

About This How-to
Author: moonwell
Added: 05.17.03
Updated: 02.26.04
Discuss (29)
This how-to shows you how to install an aftermarket underdrive crankshaft pulley. The install uses the Fast Forward Performance pulley, but the same applies to pulleys from other manufacturers. This pulley is 19% smaller than stock (4.95" vs. 6.1") and is 3 lbs lighter (1 lb 12.9oz vs. 4lb 14.5oz). The smaller size, and reduced weight, free up horsepower that is robbed by the accessories. This is good for a dyno proven 5-6 HP max power increase at the wheels, possibly more, due to conditions during the dyno runs, with a 10hp increase at the top end.

This pulley was installed on my car, and ctimm_rs was nice enough to provide the garage and tools for the install. There is definitely a seat-of-the-pants improvement in performance.



How To Do It

Step 1

Gather up all your parts and tools

pulley pulley pulley pulley pulley

Step 2

Remove the protective serpentine belt cover by removing the 3 10mm bolts. Two are on top and one is on the side. This piece also contains the serpentine belt routing diagram, in case you need it when installing your new belt. Optionally, remove the serpentine belt now, or see step 5.


Step 3

Raise and securely support the passenger side of your car, and remove the passenger side wheel.

Step 4

Remove the splash guard from the wheel well, so you can access the pulley. There are 7mm, 10mm, and torx screws holding the piece on. Some of the screws are hard to see/get at, so make sure you get them all.

pulley pulley pulley

Step 5

With the plastic out of the way, you should see the crank pulley staring back at you.

pulley pulley

Step 6

Remove the serpentine belt. You can wait to do this step now, or you could have done it before the vehicle was raised. Use a 3/8" breaker bar, or brute force from your hands to twist the tensioner pulley up, taking the tension off the belt, so you can slide it off the pulleys.

Step 7

Remove the center bolt from the pulley using an 18mm socket. An impact wrench comes in very handy here, because the pulley will want to turn as you crank off the bolt. If you don't have access to an impact wrench, you will need to wedge a pry bar through the pulley into the flex plate, to keep the pulley from turning.


Step 8

With the bolt out, it is time to pull off the pulley. You will need a 3 finger/harmonic balancer puller. It is pressed on tight, so you can't just pull it off by hand. Screw 3 3/8-16 thread bolts through the puller, into the 3 holes in the pulley. Once you have each bolt equally threaded in, tighten the center bolt, to force the pulley off the crankshaft.

pulley pulley pulley

Step 9

With the pulley off, it is time for an optional, but recommended step. The replacing of the front crankshaft seal. Mine was leaking, so it needed to be replaced, but even if yours isn't leaking, it is likely it will start to leak due to it becoming brittle, and the new pulley being installed. Using a special seal puller tool, or carefully using a screwdriver, pry the old seal out of the opening. Be careful not to gouge sealing surfaces, but don't worry about damaging the seal, since you are replacing it.


Step 10

Apply grease to the inside edge of the new seal, and use a large socket to evenly press it into place. Be sure to get it in straight, because it will be a pain to straighten out if it goes in unevenly, and you risk damaging the seal trying to correct it. Be sure the seal is in as far as it will go.

pulley pulley

Step 11

Apply silicone sealant to the inside bore of the new pulley, and in the keyway (the notch) to prevent an oil leak. Apply grease to the outside sealing surface of the pulley.


Step 12

Push the new pulley onto the crank as far as you can by hand, lining up the keyway with the tab on the crank. If it won't go on, carefully and gently tap it on using a large socket and hammer. This isn't recommended, so if you do it, be careful, as too much force can damage the crank. You only need to get it on far enough for the bolt to reach.

Step 13

Insert the center bolt and tighten. An impact wrench makes this much easier, since you don't have to deal with the pulley turning. If you don't have an impact wrench, you need to keep the pulley from turning as you tighten the bolt. This isn't as easy as it was when removing the old pulley, since the new pulley does not have openings to stick a prybar through. 76 lb.Ft is the torque spec for this bolt.


Step 14

Route your new belt. This belt should be exactly 1.5" shorter than stock. I used a 695 belt, because stock was 710. This varies depending on your alternator size, and whether you have AC. The last 3 digits of the belt part number is its length in inches. So 710 is 71" and 695 is 69.5". The routing is best started from above, then finished routing from below. Leave the belt off of the alternator pulley, and route it around the rest. Be sure to route it properly. Use a breaker bar to pull up on the tensioner pulley so you can complete the install by pulling the belt over the alternator pulley. Make sure the belt is properly seated on all of the pulleys, so it doesn't fly off, or lock up.

pulley pulley

Step 15

Reinstall the splash guard (this can be a pain to get repositioned correctly), and the serpentine belt cover. Reinstall your wheel, and torque down the lug nuts. Lower the car.

Step 16

That's it, you're done! Fire up the engine, and notice how much quicker it revs. Make sure there is no oil leaking from the crankshaft seal, and take her for a spin!


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