[msata7273]

Cranking issue on 72 TA.
I apologize for the verbose message but I wanted to be specific as possible.

Condition/Situation --- When cranking the engine, starter will crank, when the key falls back to the run position, starter keeps cranking. When turning key to off-unlock, off-lock, accessory, starter keeps cranking. The coil wire to distributor is disconnected so engine doesn’t fire. I initially discovered this condition when I was taking the car out. The starter cranked, engine fires, starter remained engaged while engine running. Fortunately the engine stalled. That was fun.
The next day I decided to take car out again, this time it cranked, engine fired, starter disengaged when key returned to run position. Seems like intermittent condition. After the drive, came back, shut engine down, disconnected the coil wire, went to start engine, starter cranked, returned key to run position, starter kept cranking and cranking, other positions as well …. Disconnected the negative battery terminal to kill the cranking.

What has been done to date ---- I replaced the key tumbler, sourced the conquers version (supplier from PA) from Ames. Installed per supplier instructions and manual. Checked tumbler, all key positions work. Comes out of gear in run position, key comes out readily in off-lock position, accessory position works, radio comes on. The lock plunger looks like it is in correct positions for all key positions. My thinking is tumbler installed correctly. After tumbler installation I ran the same test, starter cranked, let key return to run position, the starter kept cranking. Killed cranking by disconnecting the negative battery terminal. Next, replaced the column mounted ignition switch, sourced from Ames. Installed per supplier instructions. All key positions checked as mentioned above. Ran the same test, turned key to start position, starter cranked, let key return to run position, the starter kept cranking. Killed the cranking by disconnecting the negative battery cable.

Couple of ?s and thoughts 
1. Can the switch in the starter solenoid remain stuck closed even though the key is returned to run position? Ie, the solenoid contact in column mounted ignition switch is not bridged/connected through battery.
2. Has Anyone experienced this type of failure mode in the starter solenoid?

I had the starter rebuilt, new solenoid etc. I will install it next. I think there is a low probability the starter is the culprit at this point being rebuilt. If the condition does not reoccur then I believe there was some failure mode in the starter solenoid switch circuit. If this condition reoccurs then I’ll take the next few test steps:

Next steps to potentially exonerate column mounted ignition switch :
1. Start with key in off-lock position, connect negative battery cable, if starter does not crank, this implies the solenoid contact on the column mounted ignition switch is not bridged/connected (ie open circuit to starter switch side of starter solenoid). If it does crank, then ignition switch is the possible issue, either adjustment needed or bad. Problem I have here is previously the cranking continued in all key positions but possibly this will let me know something is going on in ignition switch.
2. Next move key to off-unlock position, if starter does not crank this implies the solenoid contact on the column mounted ignition switch is not bridged/connected. If it does crank, then ignition switch is the possible issue, either adjustment needed or bad. Problem I have here is previously the cranking continued in all key positions but possibly this will let me know something is going on in ignition switch.
3. Move key to run position, if starter does not crank this implies the solenoid contact on the column mounted ignition switch is not bridged/connected. If it does crank, then ignition switch is the possible issue, either adjustment needed or bad. Problem I have here is previously the cranking continued in all key positions but possibly this will let me know something is going on in ignition switch.
4. Move key to start position. I expect starter will crank. Let key return to run position. If starter shuts down, conclude there was a failure mode in the starter solenoid which resulted in the switch in solenoid remaining stuck on. If it continues to crank, I’m stumped.

I anyone has any suggestions or thoughts it is greatly appreciated.
Thanks for the help. Mike.

[johnta1]

I'd say the starter needed more shim?
Or the bendix is sticking?
Or spring in solenoid weak?

The starter pinion comes out when cranking, this makes a connection to crank. If the pinion does not go back it will keep the contact live, which continues the cranking.

If it had a remote solenoid setup like the ford solenoid it would not continue on. (but the starter pinion would still be engaged)

[TXSTARFIRE]

I have had this happen before and it turned out to be a bad solenoid. When disassembled the disc had fused to the two contacts. This could have been caused by excessive current draw, not sure but problem went away with a new solenoid.

[mlewisariz]

Sounds like a solenoid issue. Could be a broken spring or piston bore is warped Replace the solenoid with a hi-temp unit. (brown Bakelite cover)

[necdb3]

Sounds like the starter solenoid spring is broken or missing to me.

[unruhjonny]

sounds like a starter issue to me as well.

i have understood that if not shimmed correctly the starter can essentially get hung up where it cannot release.

[msata7273]

Circling back on this.

Thank you to everyone that provided feedback and advice on this thread.

Starter was rebuilt including new solenoid.

Problem solved. Finally got it back out last weekend. Starts great, shuts off great. Ignition tumbler and switch feel great as well.

Again, thanks to you all for all the input and advice.