It sounds like the starter is milling against the flywheel. Basically, the pinion of the starter is not engaging but is still spinning and making the terrible noise.
This is generally a starter problem, but can be linked to a few other things as well. Quick checks are the battery and the two starter connections. A poor connection will not produce enough energy in the solenoid to engage the flywheel. This is a low possibility but easy to check.
The pinion of the starter is suppose to engage the flywheel before the armature/pinion begin to spin/crank. Issues that prevent this are pretty hard to determine from outside of the truck other than experiencing milling. Most likely issues are a milled down pinion that no longer has a chamfer to make engagement easier. There could be some corrosion issues around the plunger inside of the solenoid that actuates the lever to engage the pinion into the flywheel. You could also have some corrosion on the output shaft of the drive assembly. Most of these are not necessarily easy to fix.
Taking the starter off the truck is not too bad assuming you have the proper length extension for the ratchet. With the starter removed, you will be able to see the output shaft and the condition of the pinion as well as the ring gear. If the starter needs replaced, you are half way done with the problem. Looking externally and do not notice anything, you can energize the starter with a battery. Connecting only to the small terminal will make the pinion engage; connection only to the M terminal (the one with the strap) will make the pinion spin. By connection both the B+ terminal and the small one, it will engage and spin.
You can try to partially dissemble the starter which isn't very hard to do and put back together. There isn't any springs or other issues when taking it apart. Once apart you may notice some corrosion or something that you might be able to clean up. More than likely however, you will need to replace it.
This is something you do not want to let go for very long because it may end up running your ring gear if not already, which means alot more money. The starter does not randomly engage into the flywheel, there are predetermined locations. The flywheel always stops at or very near TDC of one of the cylinders. You could be trying to engage into a bad section, when it finally engages. Does it happen all the time, once in awhile or is this your first time?
My first starter did this once in awhile, but not 4 times in a row. It had a lot of corrosion issues and had to be replaced. Have anymore questions, let me know. Good luck.
Last edited by Stormsearch; 01-30-2004 at 08:05 PM.