If you've recently driven through some deep water and your starter is acting oddly this tutorial is for you. If you're looking to remove/rebuild your starter for any other reason this will also help you out.
I need to explain something before we get into it. The starter works in two stages. The starter first pushes it's gear onto the engine flywheel assembly and once it's engaged and the gear teeth mesh up, THEN the motor starts to turn. My very wet starter would engage upon holding the key in the start position but the motor wouldn't CRANK for about three seconds. Once it started cranking it wasn't labored or slow. This clued me in that the contacts on the stage two (the motor cranking) were bad. Here's how to fix it.
Disconnect battery. There are two live posts on the starter and they absolutely will electrocute your stupid ass. Get the truck in the air and put it on jackstands. You'll need the front left wheel in the air so you can take it off. I would recommend setting the wheels totally straight (makes sense later). Take off the front left wheel and the little rubbery splash guard that sits behind the brake assebly by taking out the pop rivets. It's the one right above the barcode in the picture. Also, make sure you work via a super ghetto budget lighting setup. Most importantly, be sure to drink plenty of beer.
So assuming you didn't kill yourself in step 1 we can get started. I don't have a picture for this step but women say I have a way with words. To prove it I will explain exactly what you see without the aid of a picture.
Looking in where you removed the splash guard you'll see a brake line mounted to the frame rail (the top part is all coiled up). You'll also see the steering rack coming down and if you look past that, your defunct starter. Follow the steps in THIS PDF to get the starter out. I would recommend removing the bolt on the frame rail that holds the brake line in place. Don't move it too far or you'll likely kink the line but you can get a little play in it which you'll need later.
IMPORTANT: Don't remove the lower exhaust manifold. This is strictly for pussies who failed geometry and can't get the starter out of the already sufficient window. Once you've removed the starter and everything attaching it you'll have to do a few flip turns with it to get it out. I repeat, don't waste your time removing the header, it will come out...get creative.
Look at that....you're such a boss!
Open THIS PDF.
Now on to the cleaning. Now that you're 3 beers in and likely have your hands all cut up it's time to play with some alcohol and contact cleaner! Open up the actual motor assembly which is the part that is held together by two very very long bolts. Undo those and the two phillips head screws on the back. It should come entirely apart. While you're in here I'd recommend cleaning the inside of the STARTER YOKE ASSEMBLY and also the contact points on the STARTER ARMATURE ASSEMBLY. After they look clean blast it out with compressed air to get rid of any moisture or debris. Move up to the starter brush assembly. There are 4 "brushes" that contact the armature assembly. Make sure they're clean and dry and follow it up with some compressed air too. When you've finished this put all of this back together.
I'll admit that what I told you do to above is likely not needed but you should do it anyway since the damn thing is removed. This section is likely where your problem lies. Hold onto your asses, here we go. (pictures included this time)
Remember when I said the starter was a two stage process? Well the motor cranking is stage 2. Not only that, but the motor is wired in SERIES (daisy chain) meaning that if stage 1 doesn't happen (or is flawed) stage two CAN'T happen! Look at the picture below. What we're looking at is the electromagnet assembly that engages the shaft into the fly wheel. The bolt on the right side of the starter (above the black plastic harness) is the INPUT for the live power wire. The bolt near my finger on the left side is where the motor assembly gets power. Remove the three 8mm hex head screws holding on the end cap and remove it.
Open up the electromagnet assembly and take out the center pin that's likely to be fairly ugly. There is a spring surrounding the center shaft, don't lose it. Once you have removed the center pin you'll be seeing what is in the second picture.
(step 5 continued)
Time for an explanation. In the second picture above you see two contacts. The one on the right is connected to the bolt on the right that we discussed was electrified from the truck. The contact on the left goes to the bolt on the left which will feed your motor. As you can see, the contact on the right is dirty and corroded as hell. The left one is what it will look like once you resurface it by sanding it down with fine sand paper. I tested continuity between the two contacts using a multimeter and there wasn't any. Then I looked at that center pin that was pulled out. The "washer" under the bushing is made of copper. Now, copper is used for two things and two things only, decoration or electrical connections. So that "washer" under the bushing is really what makes the connection between the two contacts that you're resurfacing. Sand it down as well so it's nice and shiny. What happens is that the actuator pulls that pin DOWN as the gear shaft engages. When this happens successfully, that copper washer slams down on the two contact points and connects the starter motor with the live power wire. Brilliant eh? So basically what's kept your starter from cranking this whole time is the corrosion on the contact points!
Once everything is all shiny blast it out with some compressed air and put it all back together (don't forget the center pin spring). Clean the connections on the black harnesses (on the starter and the truck too). Reinstall your new starter...Oh wait, I mean, the starter that you rebuilt as though you were a direct descendant of Mr. Tesla himself; and crank that bitch up.