Underdrive pulley installation
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The installation may require  a special wrench to keep the crank from turning while removing/installing the pulley.

1)  Remove  the 6 rib main accessory belt. This can be done by loosening the belt tensioner  as shown in figure 1 and sliding the belt off.
This belt will not be used with the new pulley  so it can be set aside.
Note: Don’t worry how the belt came off as you can find a small diagram showing the belt routing on the original fan shroud or figure 6 below.
2) Remove the 4 rib A/C belt. The tensioner has a 3/8” square opening. You can loosen the tensioner by inserting a breaker bar/ ratchet in this opening.
This belt is pretty tight and will take a little work to remove. This belt will not be used, so it can be set aside.

3) Remove the original harmonic balancer.
First remove the large bolt that holds on the balancer. This is easiest using an impact gun.

Removing the balancer can be done using a balancer puller or a two/three jaw puller. Depending on the size of the puller it can be grabbed either on the inside or outside. See Figure 3.

When using a two/three jaw puller  it is recommended you use a short bolt and washer (slightly smaller than the original) or something similar to cover the end of the crank (area shown in yellow in Figure 4) This will protect the crank from damage and give the puller something to jack against.

4) Install new seal with a seal installation tool or small block of wood. Use a hammer on the wood block slowly tapping the seal into place by moving the block around the circumference of the seal until it is fully seated.
5) Prep the new balancer for installation. This can be done by making sure the outside machined area where the seal runs is clean and free of paint.

Next, lubricate the inside bore of the balancer where it slides onto the crankshaft with oil (or NeverSieze) and the area where the bolt/washer  will contact the pulley. Lubricate the outside where seal rides with oil and slide the harmonic balancer onto the shaft as far as you can push it by hand. (Figure 5)

6) Apply Loctite to harmonic balancer bolt and install. Use the bolt to pull the pulley on until it bottoms out or torque to 240 ft/lbs.

Loosen the bolt and retighten to 37 ft/lbs and then tighten another 120 degrees.
7) Install the NEW size small 4  rib A/C belt and then the NEW  size 6 rib accessory belt.

8) Start the truck and inspect belts to make sure they are properly seated. See (Figure 6) for  belt routing.

Some people will add an overdrive pulley to the alternator. To remove the factory "overun" pulley requires a special splined removal tool. The only reason you would add the overdrive pulley is to bring the charging rate at idle back to the normal rate. This might be recommended for guys running big amps and e-fans. Click here to see a comparision between the OD pulley and stock overrun pulley. (OD pulley is the smaller one being held)

Belt info

Accessory Belt with Crank pulley only: Gates K060895 AC Belt: K040345
Accessory Belt with Crank pulley & Alt pulley: Gates K060900 AC Belt: K040345