A couple of times now the starter on my "66 with a 240 does not disengage once the engine starts. I've quickly shut off the engine and then restart and everything is fine. What can cause this problem?
Thanks
john

 

The solenoid has the two smaller I and S terminals. When you turn the ignition switch to Start it completes the circuit which energizes the solenoid coil and moves the slug to complete the heavier gauge starter circuit which engages the starter. Then when you let off of the key and it rotates back to the Run position then the S is no longer energized and the slug, which is spring loaded, moves away from the heavy terminals and disengages the starter circuit and the starter should stop spinning at that point.

I'd suspect solenoid first and ignition switch second.

It's been a while but I believe you can test the ignition switch by pulling the S wire on the solenoid and then while a helper keys the ignition switch (transmission in neutral and parking brake applied for safety) to the Start position, another checks the voltage from the wire to ground. Should get the 12+V DC when the helper turns the key all the way, and then drop back to roughly 0V DC when they release the key. But, if it is intermittent you might not catch anything doing that, either.

.

 

TA has the best answer, but for what its worth
I replaced my ignition less than a year ago and the return spring slowly bot worse and held the switch on"start" after release. I again, went to NAPA and replaced it. The new China one is worse. does it more often and I find that you have to manually turn to "run".
Looking for a better switch.

 

Thanks for the input. I haven't had a chance to check anything yet but I do know that the PO did replace the ignition switch.
john

 

The starter may be stuck in the flywheel. Not uncommon on pole shoe starters The return spring on the movable pole shoe can get weak or break. Or the starter drive can stick on the armature shaft due to lack of lubrication or corrosion.
If the starter remains engaged to the engine and the truck is driven the starter will eventually designate it's self when the armature windings depart the armature due to excessive RPM.

A quick test. Pull the coil lead. Turn truck over it will not start. Let key go to rest so the key would be in the run postion.

Check for power on the switched side of the starter relay. If you have power disconnect the S wire on the relay and check for power on the switched side of the relay. If you have power relay has failed. If not check for power on the S wire, if you have power suspect igntion switch.

If neither have power the starter is stuck in the fly wheel. Give the starter a rap with a hammer on the body of the starter. try hooking the S wire back up and ignition coil lead. And try starting the truck, If the starter fails to disengage remove and replace the starter or disassemble to to see what has failed.