Starter ocassionally stays running after disengaged from flexplate - PeachParts Mercedes-Benz Forum

fahrvergnugen · #1 08-25-2016, 11:15 AM

83 300TD
Weird problem. It's happened three or four times in the last 2 years of owning this car. The only way I can get it to disengage is to disconnect a lead from the battery and wait for it to cool down. There is no stray wire from the solenoid to the starter main that could jump the proper circuit. The starter was new/rebuilt when I got the car; a friend installed it for me, but I can't recall the brand. Last time this happened, it was a year and a half ago. I took the starter out yesterday and tried to see the problem but couldn't find anything except perhaps a dry shaft on the Bendix. I greased it up, hoping that was it (but it isn't).

I read on here about a possible guess, that the shift interlock is wonky, but that still doesn't completely explain it. I should add, when this happened yesterday, I immediately shut off the key, and the starter still ran.

Anyone else have this trouble? TIA

jay_bob · #2 08-25-2016, 12:20 PM

The solenoid has two functions
- push the pinion into the ring gear
- complete the circuit to the motor

When you turn the key you are energizing the solenoid coil (via the small terminal) This pulls the arm in which pushes the pinion into the ring gear. Also at the same time a set of contacts makes the circuit (between the two big terminals) to send battery power into the motor.

Sounds like the solenoid is not pulling back all the way to break the circuit, or the contacts are sticking.

In either case you are looking either getting the starter repaired or replaced.

Especially since you said the starter continued to run even in the off position.

fahrvergnugen · #3 08-25-2016, 01:22 PM

Hmmm, that's the only thing that makes sense. I will search for pictures of the solenoid on these cars so I can see what I might look for there, something not quite right or something that needs to be modified.

Thanks.

fahrvergnugen · #4 08-25-2016, 01:58 PM

A private reply I got from a friend...

"When a starter continues to run with ignition key off, the problem is the contactors in the stater. These are two copper discs that allow battery current to flow to the carbon brushes.

The copper contacts weld together due the amperage loading heat.....like a welding rod.

They are made from copper so this welding should not happen .

It is likely the return spring of the solenoid is weak.....or solenoid plunger hanging up more than it should in it's bore.

DO NOT GREASE THE BENDIX OR CARRIER SHAFT. Dirt will case it it seize. Only grease the teeth of the flywheel."

Indeed, sounds like the contacts are welding. And that, they aren't made from copper like they are supposed to be. SO, I will be taking the sucker down soon and getting it properly rebuilt.

my123ca · #5 08-25-2016, 08:41 PM

In my case it was the starter switch. My original starter suddenly turned on while i was driving. I suspected the starter bendix since it was over 30 yrs old. It didnt just happen once. The last time it happened, the ring gear ate the bendix gear which left me stranded at work. When I installed another starter, it happened again. So, for now, i rigged up a push button switch. I still use the key for the vacuum and other accessories. All is good now.

Graham · #6 08-25-2016, 08:50 PM

You need a new or rebuilt starter.

optimusprime · #7 08-27-2016, 07:46 AM

If this problem is still outstanding then i would change the starter switch .If it gets grease in there it will short out and never throw back out. Had this on one car i had after putting some grease on the key as it was a new key and hard to put the key in.

Graham · #8 08-27-2016, 10:33 AM

Quote:

Originally Posted by optimusprime

If this problem is still outstanding then i would change the starter switch .If it gets grease in there it will short out and never throw back out. Had this on one car i had after putting some grease on the key as it was a new key and hard to put the key in.

Was that a Mercedes? On our cars, the cylinder/tumbler the key goes into, is completely separated from the electrical part of the ignition switch which is located at back of switch assembly. Puzzled how grease was able to get to the contacts and create a short. You should never put grease in a tumbler anyway. Graphite is the recommended lubricant.