the car in question is an 83 240d. sometimes the starter does not respond to the ignition key i.e. it does not turn over the engine when the key is in start position. have been tapping in the starter with the tire iron. and not hard. to date starter responds to the tapping by functioning. i surmise i must repair/replace starter. any insight as to why the banging causes starter to respond appropriately?

I've had this happen on several vehicles, including my 300SD. The bendix in the starter (to be more precise, the clutch inside the starter), siezes up with wear and tear, or if defective to begin with. Banging on the starter (particularly on the bendix end) can free it up long enough to work, but this isn't an attractive option (particularly in rain or snow), and it will usually get worse over time. You can rebuild the starter, but I've usually just replaced the whole thing, as starters aren't all that expensive as a rule, and are fairly easy to replace.

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1980 300SD (The Green Machine!)
180D Ponton (paid $100 Cdn - sold $200!)

I agree with Green Machine, striking the starter to get it to work does not bode well for the future - the starter will probably completely fail to work at the worst time. Make sure when you replace it that you get starter made for the diesel engine (the gas starter will fit, but is not designed to handle the higher compression your diesel has).

I wrote a lengthy reply on how to R&R the starter a while back (with useful comments from other members). Look for a thread started by New to MB entitled "How much trouble is starter" dated 12-28-01.

Good Luck!
Tom

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America: Land of the Free!

1977 300D: 300,000+ miles

American Honda: Factory Trained Technician & Honor Grad.
Formerly:
Shop Foreman;
Technical Advisor to Am. Honda;
Supervisor of Maintenance largest tree care co. in US for offices in Tex.