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Outstanding Contributor
450slc5.0cab 280sl5sp 280se4.5 500seAMG +250seStkW108 350sl4spdX3 500secEuro
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22,159 Posts
Discussion Starter #1
I was surprised it seemed to work fine outside the car, but in the car even without spark plugs, it cranked the car slowly. Before I go get another starter, I’m seeking opinions. I think I have a video of it cranking the motor. This is a 1973 350slc 4-speed, but this w126 is the most popular forum, and I figured I’d get the most action here.


Thread in 107 forum where I’m documenting the full wiring + starter concern:


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1991 560sec. 1969 280SL
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1,040 Posts
Its acting like it’s weak. I would take it apart clean it check continuity of the armature and if need be replace the brushes.
 

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Outstanding Contributor
450slc5.0cab 280sl5sp 280se4.5 500seAMG +250seStkW108 350sl4spdX3 500secEuro
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22,159 Posts
Discussion Starter #3
Its acting like it’s weak. I would take it apart clean it check continuity of the armature and if need be replace the brushes.
Thank you. That’s what I wanted to hear. I want to know that I pulled it out for good reason, not just a bad ground.

It’s deceiving because the solenoid pops out so well, making you think it’s got torque, but you can hear the acceleration in the video. That took me a few tries to really notice it.

I wonder if this bad starter is the sole cause of the white wire to my old style voltage regulator melting (when I cranked too long).

I need to put a tag on it that says “weak starter from 1973 350slc 4-speed” and drop it off at Jason’s shop and grab a good one from down there.
 

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350SDL, '17 GLS450, "Grandpa's Roadster" Project Car
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I disagree. It looks OK to me. Take the cover off the brushes and look at the brushes and commutator. The commutator should be clean and copper colored. The brushes should be long enough that the springs pressing them against the commutator are not getting close to the brush holders, where they will stop applying pressure. The whole starter should not smell "burnt". If they look (and smell) good it's probably not the issue.

Most starter problems are bad connections. Second would be bad contacts in the solenoid (measure the voltage drop between the starter solenoid battery terminal and the terminal where the solenoid connects to the starter motor with the starter motor running.

Or, the engine (in the car) could be seized.

Do not sun the starter with out a load for more than a second or two. Series wound motors are not self regulating speed wise and it will overspeed and overheat very quickly. First thing that usually happens is the solder on the commutator melts and flies off. Then it's a core at best.
 

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Outstanding Contributor
450slc5.0cab 280sl5sp 280se4.5 500seAMG +250seStkW108 350sl4spdX3 500secEuro
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22,159 Posts
Discussion Starter #6
I got two used starters from @rwd4evr ‘a shop and notice potentially less acceleration from the starter that had a wire still on it. I will see if I can video the “difference”. It’s definitely not super noticeable. The one with wires does have a positive battery cable. So I can test using that wiring setup. I did ground the old starter.

I guess it’s possible I might never know the real problem. I might bolt in the starter that has the wires ASAP, but I will video them both first.


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