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I have a 1981 w123 240d with manual transmission. I recently parked my car and when I came back after a few hours and turned the key to the start position. Nothing happened. The starter motor didn't spin and the the solenoid didn't click. The battery seemed to be charged and the instrument lights were on.I went to the starter and bridged the connections for the starter motor and the solenoid with a wrench. There were a few small sparks but nothing else. Not like the sparks you usually get when you do this. I was on a hill and started the car by rolling down the hill and popping the clutch. I drove home and the idiot lights were off and the alternator seemed to be charging. When I got home I killed the engine, I tried to restart and it started and restarted in the usual way several times. I went back to the starter and bridged the solenoid and starter motor connections as before. This time the starter motor spun but didn't engage the fly wheel. The solenoid didn't throw. Do solenoids sometimes work intermittently or do they just go completely dead? Thanks for any advice.
 

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I'm not familiar with your exact starter, but yes, they can do this and it's quite common. Sounds to me like the solenoid is bad. A redneck fix to get it started that I've done many times with various cars over my life is to hit the solenoid hard with a wrench, hammer, or whatever. The solenoid is pretty much the reason of most all starter failures. The normal setup is a winding, which any electric solenoid has, and when DC is applied (12V in your case) that winding generates a strong magnetic field that moves a fat steel rod going thru the center of it. Picture a roll of string wrapped tightly around a cardboard tube, which is how string often comes. Make that string copper and slide a metal rod inside the tube and that's basically it. This rod moves a lever which slides the gear on the starter out into the flywheel. So in your case I'll assume the winding wire is broken, which is typically how they fail, and is just barely making contact so depending on the temp causing expansion or contraction of the solenoid, it will either barely spark and nothing happens, or work well enough and off you go. Normally the winding is encased in epoxy to protect it, but imo this is also why the wires breaks. If they had used silicone rubber I believe it would last forever.
There's also contacts that turn on the motor itself and when those get burnt enough they stop working, which is the classic loud click of the solenoid working, but no spinning, but often if you keep trying it will find enough copper to make contact and start the car. A redneck fix for that is to use a Ford solenoid that is not attached to the starter so you're bypassing the internal switch and using the Ford unit to switch it on. A low batt will do that too because the batt can drive the solenoid no problem, but no current to turn the motor, but in this case your dash lights will also dim to almost nothing as the batt tries to turn your engine. I mention those for others searching the forum for fixes because it won't help you. You need a new solenoid...
Your solenoid will only get worse over time since the wire is broken and likely sparking a little bit each time which only burns more of the ends of the wire making it worse for next time. This is where smacking it gets you going, a good hard shock often makes it connect well enough again. If you're lucky the solenoid is sold separately, and if even luckier you can swap it out without pulling the starter, or the starter comes out easy.
There used to be a place near me that repaired starters and even sold all the little parts if you needed, and I did because I was a kid with no $. Then came the out of the country (Mexico) places that rebuild starters for cheap to sell to the lame neighborhood auto parts stores, which put that place out of business. This is a bummer because they rebuilt it correctly, these cheap places use the absolute cheapest parts and I rarely get a year out of those starters. My point being you should buy a genuine MB solenoid if possible. If you have to buy the whole starter I would at least consider MB but they probably want too much $ so I'd look for a brand new afermarket starter, NOT rebuilt. A lifetime warranty is how those places get people to buy those cheap rebuild starters, but I'd take a new one with 30day warranty, or eve no warranty, over a rebuilt with lifetime. This goes for alternators too btw... The rebuild places use a cheapo diode/regulator assy and it will be short lived. Buy new or buy a quality diode/reg assy and fix it yourself.
 

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I agree, bad starter. But there's rebuilt and rebuilt - that is you can get a started rebuilt by Bosch for maybe $100 or the Bosch solenoid for $50 and do the work yourself. Or you can go cheaper (I did once and it lasted 1 day, no lie). I then got the Bosch rebuilt and it's still in the car 15 years later.

I'm not sure you can find new anymore but don't fear a rebuilt one just get quality.
 

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Back in Sep 2019 I had what appeared to be a Starter Solenoid issue. When I took the starter apart I found that the brushes were extremely worn.
I bought a new Bosch Starter Solenoid and a new Bosch brush Set. One of the members of another forum had said that the worn Brush will cause the solenoid issue.
To see if that was true I re-used the old Solenoid and the starter has been working fine with the old Solenoid since 2019.

Not that the original brush wire ends are welded to the Brush holder and the 2 field wires. However, the Brush Holder and the Field Wires are already set up with holes so that if you are sure you buy a brush set with metal tabs and holes in them with the screws and nuts you just cut off the old wires and assemble the new stuff with the provided screws and nuts.

Find a forum that has a good starter rebuild thread.
Note the Monark company makes a starter repair kit that not only has the brushes but bushings and other part. However perhaps because of the virus I do not see the one one for my 84 300D selling on eBay right not.
 

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I forgot to mention the Bosch Starter Brush set back in 2019 was a total cost of $16. And unfortunately the Philips head solenoid retaining screws stripped out so I replaced those with Allen head screws from a hardware store.
So it only cost me $16 to get the starter working and nothing else was worn that needed to be replaced.

I will save the new Solenoid I bought may need it later or I can sell it.

Find a thread on removing the Starter as that is the difficult part of the job.
 
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