puzzling starter problem
 

The problem started when I would turn the key and no starter !!!
So, its the solenoid right ?? Well, I replaced it with a known good starter from another 300SD. It worked for a bit but within days I saw the problem again. In all these cases I could use a screwdriver to jump the 'S' terminal and the + terminal and start it.
Or, just short it for a second and then it ALWAYS cranks using the key.

Thats the puzzling part,

When it became more and more frequent I swapped in a 'brand new' starter, redid the wiring from the battery and the bus on the fenderwell. All new wires, heavy guage wire from the battery positive etc:-

worked great for 2 days and then the same symptom.

what gives ?


this is on a 1980 116 body 300SD

could be your ignition switch is on the way out. Worth a check
Morris

ignition switch related ...
 

except that as I said - once I kick it with a screwdriver, it will ALWAYS crank using the key.

If you swapped out the starter with a known good one and the problem exists it can only be one of a few things. While you looked after the postive cables to ensure good connections - did you check ground strap? There may be an extra ground strap from the motor to the chassis that may be corroded or the main ground may be corroded. Also - had one VW that drove me nuts with low current to the starter all connections were clean and tight but finally a resistance check of the cable to the starter from the battery showed that there was resistance in the cable. I cut it open to expose nothing but corrosion. New cable cured problem. Now assuming that the current flow to the starter from the battery and back to the negative post of the battery is perfect - the only other thing that can cause the problem is a missing 12 volts to the solenoid to kick it in ( using a screwdriver applies the required voltage and the spark will temporarily overcome a bad connection so it will work for a short time. Next time it won't start have someone take a voltmeter and check if there is 12 volts going to the small terminal on the soleniod when you turn the key on - if it is there then it has to be the starter or the current cables to the starter. If it is not there -
1) check to make sure the connector that attaches to the soleniod has the wire firmly crimped into it.
2) once #1 has been confirmed hold the voltmeter onto the terminal and play with the ignition switch and see if you can get the voltage to come on to start the car.
3) if that does not work - get to the connector at the back of the ignition switch pull it off the switch and check the continuity between the proper pin of the connector and the solenoid - if that is good - then suspect a bad ignition switch

That is all I can think of that can cause your problem.
Morris

thanks, will do the test

Get a book and follow the procedure for a voltage drop test.

Good luck,

Several GM cars had the same problem in th 60's including one of mine. But old volkswagon people know of a starter booster kit for the 6 volt models. The kit consists of a continueous duty solinoid (A Ford starter solinoid) and it's wired up like this:

10 gauge wire from starter battery to left side of solinoid.
10 gauge wire from the right solinoid terminal to the starter's Start terminal.
Start wire from ignition switch goes to S terminal of Ford solinoid.

I did this to a buddies International Scout that had the same problem. It worked fine and he said he didn't have to turn the key as hard to start it.

If you think of the princible, your starter solinoid is an electro-magnet. If you don't have the amperage to energize it, it won't work. The actual power loss may be in your wiring harness. The starter booster gives you battery amperage via the 10 gauge wire direct via the Ford solinoid. I think GM's problem in the 60's was a 16 gauge S wire in their wiring harness.

Yes I have done this as well. In fact my old 240D still has the relay in place. It does indeed help but it really just patches the intrinsic problem. If the solenoid won't kick in you need a new solenoid or starter.

If the starter is a quality rebuilt unit without excessive end play, replacing only the solenoid will get you going again. You should not ASSUME that this is the problem, however, before doing a voltage drop test so that you know that you're not just throwing parts at the problem.

Good luck,