Good evening everyone. New acct here but have been using the forums for years. Here's my issue and here's what I've noticed and read.
1985 Bronco 351w c6 trans. Since buying the bronco it had a starter issue but has gotten worse and now it's too much. Started off as grinding. Then replaced flexplate due to worn teeth. Worked for about 5 startups and then started to make the grind noise again. Eventually the gear/bendix will just spin freely without engaging flexplate but still shoots outward fully extended. Checked with a slow motion camera. Before replacing flexplate I went through about 8 starters (tried new ones, remans, Motorcraft ones, Napa ones, autozone ones, re uilt for starter shop ones, all of it!!) I know the nose difference in auto /manual, and these aren't the shimmable starters. I read the post about the thrust bearing issue causing starter to need shim however this isn't my case. Thrust bearings are good condition with no slack. I changed flexplate twice, changed starters over 10times and still here. The bellhousing holes are stripped so I use nuts on back of bolts, and this is how it came. I've had it for like 6yrs and this problem has been my constant headache haha. I read on here someone widened/oval-shaped the holes on the bellhousing/starter allowing the starter to be moved closer to the midline of the flexplate which seems like exactly what I need but I don't want to do that if someone has found another solution. So once again here's where I'm at. Starter is too far away from flexplate, too far out from center making the teeth grab at the very tip so it works after swapping but grinds and slips, and eventually wears out the teeth of flexplate a little and then causes starter to spin freely too far from flexplate to engage. Worst feeling ever is not being able to solve this problem. Sorry so long, I truly appreciate everyone's input and if nothing else I'm glad to be apart of this group.

 

You are mismatched somewhere if you are going through ring gears and starters like that
Ford made at least a dozen drives (starter drives) and yours may be the wrong number of teeth
Have a Ford parts man verify the number of teeth on a SD 302 or whichever one your starter takes
The aftermarket drives are so chitty these days and good luck finding a ford drive
That is what your truck wants... And a new C6 case

 

I did, I had gotten my starter from Ford and they ran the Vin to get it. It was different than the autozone and Napa starters that I had previously gotten, but when I bolted her up it did the same thing, spin freely without engaging the flexplate. After I swapped the flexplate, I put the new dealership Starter in and it was grinding then eventually not touching the flexplate at all. I know the flexplate is the correct one, verified it through all autoparts stores and then measured it and weighed it and counted teeth and all the flexplates were identical from what I can tell.

 

I would not just blindly trust what the dealer gave you either
I agree that the flex plate is most likely correct
I want you to check the drive available from ford that fits your application
For instance the SD 302 Motorcraft drive has 9 teeth
You may need one with 10 teeth
You may need a different nose

 

Yeah I went outside today, rebolted the starter using a bit thinner bolts and nuts and kept it closest to the flexplate as possible and it cranked beautifully. Problem is after after about 5 or 6 startups it started to grind and then stopped engaging flexplate completely but still has the gear extending and starter is running correctly. I think my bellhousing/tranny bolt holes are off since they're already stripped and requiring nuts to at the end of the bolts to keep em tight.