1995 F250 5.8L. Almost home and heard a loud grinding noise, Pulled into the driveway shut the truck off but the starter kept grinding. Disconnected the battery to stop it. Smelled smoke from down by the starter. Solenoid was cool to the touch. Hooked the battery back up with the key off and the starter spun without hearing a click from the solenoid.. Removed starter and noticed the outer edges of the gear that engages the flywheel worn off. Hooked the battery back up and turned the ignition switch to start. Heard the solenoid click like normal. Any advice you can give me? Thanks.

 

If your starter solenoid is energized by the ignition switch or the contacts are fused together, your starter will continue to spin.
When this happens and the engine is running the bendix gets chewed up.

To be safe, replace the starter solenoid with a high quality one.

Your starter may or may not be usable.
Your ignition switch could cause this if it is failing and enrgizing the solenoid. You should watch/listen/measure for this possibility.

Usually this event occurs when you are starting the motor, the solenoid contacts are closed for the reasons above.
If this happened later in the drive, I would check the ignition switch.

 

I would agree with you except the neutral safety switch should have broken the circuit not allowing power out to the solenoid. While I would check the ignition switch, I would probably start by checking continuity at the solenoid and see if it's closed with no power to it. If that's the case it's junk and needs replaced.
As I see it, the ignition and NSS would both have to fail in order to power the starter while driving.

 

nope. when the solenoid welds the contacts inside, it will keep supplying power to the starter even if you take the trigger wire off.
only way to kill power to the starter is to disconnect the battery cable.

 

Right, but he said the noise started while he was driving. So there should have been no way for the contacts to weld since there should have been no way to get power to close it in the first place.

 

Yeah, i forgot about the NSS...

 

in the real world you are correct. but i have seen the solenoid fail and engage the starter way to many times over the years all on its own without any trigger power being sent to the solenoid.

 

Be helpful to know if this truck is standard or auto, but ether way, the complete circuit should be checked.

 

Oh trust me, I've seen the all to easy, " that shouldn't have happened ". That's why I suggested checking to solenoid to see if it's closed while not powered by the signal wire.

 

The starter is the typical late-model PMGR type, correct? This should have the solenoid piggybacking the starter motor, with the starter relay still mounted on the fender.
This style gives constant power to the solenoid from a direct connection to the positive side of the battery, so even if the relay on the fender is perfect, a fault down at the solenoid could cause trouble as well.

So as said, check all the wires. You may have heat damaged old cables or jumper wires to the solenoid shorting to the motor contact. Or any of several other problems that can cause issues.

Paul

 

Paul, a 95.8 should still have the fender mounted starter relay/solenoid that is prone to sticking and keeping the starter engaged.

 

that's the mystery for me--that the starter spun up while i was driving. since the starter smoked i knew it was bad anyway so i replaced it, drove to work today with no problems. i'm not saying it's fixed because i haven't checked the wiring (not much of an electrician) but based on today it looks like the solenoid on the starter went bad while i was driving.