Starter Motor Stuck

[Scrubmonk]

I have a VS V8 Auto.
New starter motor was put in about 5 months ago when the old one completely died and has been working fine until last weekend when it suddenly refused to turn over, and had to get towed home by the RACV.
I have plenty of battery. The starter motor makes a clunk, being the solenoid activating when you try to start it, but then nothing. Gave the starter motor a bit of gentle nudge with a large heavy object, but still no go. Tried it with the car both in Park and Neutral.
Got a replacement starter under warranty, installed it, and guess what - same thing - still no go.
Bench tested old starter, works no problem. Tested starter wiring circuit, no problems.
Got a socket onto the crankshaft/balancer bolt, manually turned over the engine a few times. Engine turned over normally.
Tried the starter again, now it works no problems.
I am happy that it is going, but won't be satisfied until I know why it happened in the first place.
Any ideas from people with a similar experience? Stuffed ring gear maybe?

[Sabbath']

Could be missing some teeth on the flywheel/flexplate. And when it stops in that area, there's nothing for the starter to turn. Hence your problem.

[Scrubmonk]

Could be missing some teeth on the flywheel/flexplate. And when it stops in that area, there's nothing for the starter to turn. Hence your problem.

If that was the case, then when the starter motor hit that point I would expect the starter motor to spin freely. It doesn't, just totally refuses to turn at all.

[m1lky]

Can you try with the starter out but connected to the car turning it over? I'm thinking maybe there's an issue with the wiring and it can't supply enough current?

[Hangman]

Can you turn the engine by hand?

[James39]

Can you turn the engine by hand?

Yes, as he said.....

Got a socket onto the crankshaft/balancer bolt, manually turned over the engine a few times. Engine turned over normally.

[Hangman]

Yeah, missed that line. Obviously.

[Scrubmonk]

Thanks everyone for their replies. I am convinced that it is something mechanical rather than electrical as the starter tested OK out of the engine. The new starter is working as it should, once I cranked the engine over by hand a few times.
I starting to wonder if maybe something has come loose in the flew plate area, and is randomly jamming the starter? If I end up having to take the auto out, it will definitely be a manual box going back in.

[sleepyjean]

checkthe wiring to the starter. it could even be a relay, it doesnt sound mechanical as the started tested off the car, it sounds like the solinoid is throwing out but there is no drive to the starter in the car???

[Scrubmonk]

It did it again the other day. Turned the engine over by hand, still no go. Notice that the leads on the positive battery terminal were a bit loose. Tightened them up and away it went. My guess is that it was getting enough current to throw the solinoid, but not enough to turn the starter. I hope this is the problem, as it was an easy fix.