I have an 85 f250 460 w/ 4 speed that has been driving me up the wall. When i try to start it the starter just spins free and does not engage the ring gear. I have replaced both the Starter and Starter relay/solenoid 4 times each. Every time i replace them it starts well for about 2 weeks, followed by a week of spotty grinding starts, followed by a complete lack of engagment. Sometimes if i jolt the starter (such as an attempted bump start) it will grind start once, but its spotty at best. The ring gear teeth themselves show some wear but nothing i wouldn't expect out of a truck of this age. Does anyone have any idea whats going on? I cant afford to replace my starter every month and i really want my truck back!

 

If there is insufficient power available to the starter motor it might attempt to engage but not have enough to hold it in engagement with the flywheel.

At this point it is time to check the battery cables and connections. The best way to do this is with voltage drop testing OR replace them. Of course there could be a problem with the starters. Make sure you are getting the correct starter.Auto trans starters are different from starters for a stick shift.

 

I had the same problem, changed starter and solenoids. Then found the factory battery cable was corroded INSIDE the lead post clamp. This allowed just enough juice to show voltage on a voltage meter and light gauges but not enough amps to engage starter. I replaced cable ends from Walmart and now I have a Spare starter.