It's been the second time now it's been doing this.
The car starts fine, the sprocket disengages from the flywheel, but somehow the starter motor keeps running.
Just turning the key to "off" and pulling it from the ignition won't stop it. I have to disconnect the battery in order to stop it.
Defective relay or do I have to pull the starter?

Sounds like a bad solenoid. You'll have to pull the starter to fix it if that is the problem.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Why don't you call the auto club?

Starter solenoid is not disengaging. Depending on the miles on your current starter you might want to consider replacing the starter also as it is a bit of a chore to change the starter.

Thanks for the replies. Much appreciated.

I found this here:
starter issues

The car is in the driveway. I will just take another car. It's not an urgent matter.
As I said, it is the second time this happened, so I am not surprised about it.

I was trying to see if there is an external reason that could cause this problem.
The trouble shooting chart attached shows a binding ignition/key but it doesn't seem to be the case. The tumbler feels fine.
If the starter has to be pulled, it will be a job for the mechanic. Will call AAA for a flatbed some time this week.

Attached Thumbnails

 

If the sprocket disengages from the flywheel, then there is no problem with the solenoid. I bet its the switch. My starter would engage once you turn the key from the off position and would continue to engage even when the engine had started. It was like i never let go of the key. I still had to replace the starter because the bendix wore out. The starter ran while i was driving.

Remove the two wires(violet and red) on the RH wheel well(C105). Secure the terminals with electrical tape. Turn the ignition key to turn on the glow relay and start the car by bridging the two terminals in C105(I forgot which two). If it starts normally you just confirmed its an ignition switch problem. I dont think there is any relay in the starter.

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'85 300D Cal 280,000 miles
'14 GLK 350 60000 miles

I'm not sure how you know it disengages from the flywheel... But he ONLY thing that powers the starter motor is the solenoid. The solenoid armature may be engaging and disengaging correctly, but the contact plate inside is likely arc damaged and has welded itself to the connections. A new solenoid, or repair of the original one will solve the problem.

Maybe you cranked the motor too long recently and caused ring wear...

__________________
John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

This picture might help. For the motor to keep running, the contacts at the LH side of the solenoid must be closed. For that to happen, the solenoid coil must be receiving power. Could be that switch is malfunctioning and maintaining power to the coil even when you release switch. Not sure if pinion will retract once engine starts without breaking contacts. If it does, it should not. But perhaps the clutch slips? So even if there is a switch problem, it would seem that there is also an internal starter problem?

From experience, once you have a starter problem, a new or rebuilt starter is the smart fix. I read on Vintage forum where someone picked one up at O'reillies for about $100. I bought one on eBay quite a few years back for my SL for $99 and much earlier had my 300D starter rebuilt.

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

Thank you again.
I assume it disengages from the flywheel, otherwise it would make a terrible noise!?
Yes, I could have driven the car, but it certainly didn't seem like a good idea. Besides, since the starter keeps running for as long as the battery is connected, I cannot restart the car.
There is some smoke/smell coming. It maybe from the overrunning clutch.

under normal operating conditions, yes... however, if you look at the ring and pin that the solenoid hammer hits, you will see if the ring welds itself to the contacts, once the solenoid no longer has power, from the key being released, the starter motor will still have full power.

it's SCARY, and zero fun when this happens...

__________________
John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

Question. If contacts are welded closed, would that not happen every time battery is connected rather than intermittently and only after starter switch has been used?

In other words, if EI Ted disconnects battery to stop motor from running, then, if contacts are welded closed, shouldn't motor just start up again without using starter switch when he reconnects? Sounds as if once battery has been disconnected, he can start using the switch next time. And then motor may keep running or not.

If above scenario is correct, then perhaps it could be a switch problem?? (power kept on solenoid intermittently)

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

The last time (first time) this occurred, the starter stopped running after several minutes being disconnected. To be accurate: I reconnected the battery, starter was still running, but stopped after a few seconds.
At this point, I thought, well maybe an isolated incident. Everything operated normal for a few weeks. Until yesterday.
I tried reconnecting several times, incl. this morning, starter came on running every time.

That being said, although the starter ran, it didn't crank the engine. Just running freely.
That's how I assumed the pinion (sprocket) is not engaged with the flywheel.

The car went off to the mechanic this morning. I expect he may have to pull the starter. I will take it from there, know more soon.

Better have your 13 mm wrench on hand quickly.