Lately I've been noticing the starter on my 2006 B4000 has been a little slow. I replaced the battery on this truck last year and it rarely gets driven. As a result it sits on the battery-tender frequently to keep the battery in good shape. (all 3 of my cars do)
It got much worse last week when I was out getting ducting for the furnace on my new paint booth. I started the truck and for a second it would barely crank and I thought I was going to have to get a tow. I decided it was time to diagnose the problem.
I measured the current draw with my picoscope and I found that it was drawing around 415 amps at peak pull. My concern was the power and ground connections and I was satisfied when I saw I was losing less than a half of a volt each through the starter positive and ground connections. Battery voltage was dropping a little low (about 9.9V)
Voltage at the battery during starting:
Voltage at the starter during cranking (blue)
Current at the B+ cable during cranking (red)
Voltage drop, B+ terminal to starter + terminal (yellow)
Voltage drop, battery negative terminal to transmission housing (green)
Once I saw this graph I new it was time to buy a starter. I put the truck on my hoist and pulled off the OEM starter (it only has 26K on it).
I found that the easiest way to get the starter out was to use long extensions and go from the front by the steering rack and go over the front differential. 4WD makes this much harder to access compared to a 2WD truck.
I saw that one of the brushes in the starter was completely bound up and trapped back where it couldn't make contact. I had to unbind it with a pair of needle-nose pliers. The brush opposite this one was worn much worse and all cocked sideways. You can see below how it looks.
I rebuilt the original and it works great. Engine turns over fantastic now.