gear install parts?

Click Mo-Dingo's link in sig on gears. It's very helpful.

You also need a press.

I've heard you need a new pinion nut everytime you take it off....true?

Just make sure you get a master bearing kit for your
new gears and you will be fine.

Other than all of the tools, the Math below will really make sure it comes out correct:

Determining proper pinion depth isn’t difficult if you know how to do the math. That’s exactly what we’re going to show you, using our 8.8 Ford axle as an example. Get a calculator and follow along.
Step One
Find the diameter of the differential side bearing race (dial calipers are great for this). Ours
measured 3.063 inches. Divide this number in half to find the bearing race diameter:
3.063" ÷ 2 = 1.531"
Step Two
Measure the distance between the main bearing cap mounting surface and bearing bore as in Photo 13. Since we are working with a 1.531 inch bearing race diameter, we used a two inch extension on the Tavia pinion setting tool to get a complete reading (the indicator needle will depress a half-inch, putting us right on the money). Our indicator read .465 inch.
Step Three
Subtract the bearing bore reading from the length
of the pinion tool extension. This is the actual axle centerline. The equation for our 8.8’s centerline is:
2.000" – .465" = 1.535"
Step Four
Next, subtract the bearing race diameter from Step One from the axle centerline. This is the amount the axle housing is off-center. Our axle was off-center by .004 inch, as shown:
1.535" – 1.531" = .004"
Step Five
Now you need to measure the distance from the axle
housing centerline to the face of the pinion gear. Install the pinion gear as shown in Photo 14. Since the pinion depth marked on our Superior pinion gear is 2.552 inches, we used a three inch extension on the pinion setting tool. Measure the distance betweenen the pinion face and the axle centerline. In our case, the measurement was .416 inch.
Step Six
Subtract the reading from Step Five from the length of the pinion tool extension, as shown in our example:
3.000" – .416" = 2.584"
Next, subtract the off-center figure from Step Four from your answer. This will give you the actual pinion depth:
2.584" – .004" = 2.580"
Step Seven
To find out how much you need to shim the pinion gear, subtract the depth marked on the pinion gear from the actual pinion depth you just found:
2.580" – 2.552" = .028"
Thus, we need a .028 inch pinion shim pack.
See, that wasn’t so bad!

I have used these steps on a couple of installs and it works great.
Good Luck

When I installed my Ford racing 3.73's I was able to reuse the .030" pinion shim that was on the factory 2.73's and the backlash was fine. You don't need and new pinion nut evertime just use red loctite on it when you reinstall it. Ford racing gears are real easy to set up because of the close manufacturing tolerances.