Our '79 300D starter motor has begun to sound as if the starter cannot completely disengage from the ring gear when the engine fires- result is a not-very-pleasant grinding noise. No matter how fast you release the key when the engine fires, we get the noise.

Do these starters have the equivalent of a "bendix drive" like the Delco units I am used to?- if so, could this be the cuplrit, or could it be a defective ignition switch that is not releasing in time?

Also- I'm used to my Ford 6.9 Diesel truck engine firing almost instantly when the key is turned (way faster than a gas engine) - but it seems the 300D needs at least 6 0r 7 spins of the starter before it catches, even when warm. Is this normal for a Bosch fuel injector pump, or does it need adjustment?

Thanks to all for your help!
Nate Stanley
'79 300D
'85 F-250 6.9

In all my dealings with my 123 Starters, I've never experienced the starter hanging in the flywheel.

Yes, this starter is extremely similar to a Delco type starter with drive, solenoid and motor.

I expect that you are going to find that the starter primary circuit is the problem, not the starter itself.

To test this, simply connect a voltmeter to the primary wire(the only small wire going to the starter solenoid) and ensure that the voltage is going to zero after you release the key from the start position.

Good luck,

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Larry Bible
'01 C Class, Six Speed
'84 Euro 240D, manual, 533K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in
Mercedes automobiles

Sorry Larry,

I have seen quite a few with this problem. I would lean toward the starter as the problem.

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Benzmac:
Donnie Drummonds
300E
ASE CERTIFIED MASTER AUTO TECHNICIAN
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM
OWNER OF MB AUTOWERKS .COM

Nate, your problem with the poor starting could be a partial opening of the fuel shut-off switch when you start. Try removing the vacuum line to the shut-off switch to remove the vacuum. Then reconnect the line. Now start the engine. If this cures the problem, then possibly the vacuum bleed valve at the ignition switch is worn.

Gary

starter failing to disengage?
 

This is an open response to Sergey Vushakov, who asked me what the eventual solution to this problem was--

The problem went away when we replaced the vacuum pump.
We did not realize it was going out until one day we were going down the freeway and suddenly the power brakes got hard and the engine refused to shut off. The vacuum pump was found to have worn internal seals.

Once we rebuilt the vacuum pump, the problem went away, and to be honest, I had forgotten to supply these results to the forum.

I'm not sure why this worked, so--Does this make sense to anyone? BTW the starter, solenoid and bendix drive have not been touched and have given excellent service down to this day.

Cheers,
Nate

Donnie,

No apology necessary. Thanks for jumping in. I do now remember reading about starters hanging. I've been fortunate enough to have never experienced it on any of my cars.

Have a great day,

Thanks for the reply, Nate.
It adds up to the variety of the fixes for this grinding-after-start problem I found so far on the forum... How expensive was vacuum pump rebuid?

Sergey