That all makes sense except sometimes it works and sometimes it does not. What is changing? I can do some more testing but still confused on why it is intermittent?

I think I answered that for you, or at least gave you a reasonable possibility. When you wack it, BTW, you can jar the commutator just a tad so that the dead segment is no longer contacting the brush and then it works until the next time it lines up - completely random. I understand that you don't want to pull the starter back out but think about your symptoms and who's suggestions make the most sense.

Dan

I have one of these gadgets, if you want to borrow:

Model 8540 | Associated Equipment Corp.

It will tell you whether the battery is holding up under starting loads and simultaneously tests the grounds, starter power connection, and the solenoid lead. It works by measuring the voltage drop at each connection. Someone gave this to me as a gift, I've never had reason to use it.

FWIW, I think Dan's nailed it. A fouled commutator or one open winding would behave like this.

Here are a couple photos of the old starter solenoid:

It looks like material got transferred from the lugs o the connecting plate over time. Don't know if that's normal or not.

As far as current and voltage go... if it is just clicking and I connect the solenoid trigger wire to positive battery it still clicks.

It is only after several rapid clicks that I can get it to make a good enough connection to turn the starter over. Once the connection is made the engine turns over quickly and starts immediately.

Did you bang on the starter with an iron pipe as I suggested in #12?

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83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

You either have a solenoid that isn't pulling in all the way (far enough to close the contacts in the switch it pulls against), or you have a failing relay switch (burned points, warped contact disc, etc).

If the solenoid is pulling in with enough force to clunk you don't have a wiring issue. The solenoid itself pulls somewhere close to 20A all by itself, meaning your ground should be ok and the wiring to the solenoid should be ok as well.

You either have a sticking solenoid (pull it and see if it's been greased), or you have a set of contacts that's failing that the solenoid pulls in against. Either way Funola's suggestion of slapping the starter with the iron pipe should get it to pull in enough to operate if that is the problem.

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Current stable:
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1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Once upon a time I went through several Beck Arnely starters on the 1984 300DT which failed to work properly. I finally bought a genuine Bosch starter and life was and has been good ever since......

I had this happen. Went through same frustrating starter replacement and pipe banging. Finally noticed smoke at battery connection. Probably checked contacts already three times through the process. Dissolved the corrosion until copper was clean. Put it back together. Problem solved...for years now. That's my guess.

Did you change the solenoid when you changed the starter?

Is your new starter a rebuilt one? If so, who rebuilt it?

The starter I put in was a used one a got from a car I parted out. It looked newish (clean black paint) but no Bosch sticker.

I definitely suspect the problem is the contacts inside the solenoid.

I am close to ordering a new Bosch starter to fix the problem.

My concern is that the good used starter worked fine it first and now has the same exact symptom the previous starter had.

So it's either coincidental bad luck or some unusual problem somewhere else in the extremely simple electrical system.

Just to be clear : when the starter will not turn over it never fails to produce a consistently strong clunk sound of the solenoid engaging. When that happens with the key and I jump it between the screws at the firewall connection same exact result. If I connect directly from battery positive to solenoid same exact result.

I will bang on it today but I am sure that will work. What works now is to used my remote starter cables with button to engage the solenoid rapidly until it makes contact. You can't do the with the key because you have to turn it back every time.

It's a tough problem to diagnose because it usually starts perfectly. So I just have to wait or start and stop it a dozen times or more before it acts up.

The next time it will not start with the key I am going to try and measure voltage and see what that is. It doesn't make sense though because it usually starts fine with the key.

It's completely random as far as I can tell.

It doesn't take much electricity from the battery to get the click. I takes a lot of electricity to run the starter motor. Since you have gotten the same symptoms from two different starters and two different solenoids, I think you should go over the electrical connections again. Start with the battery terminals and the cable connections. You can clean them with a wire brush or with a pocket knife. There is a commonly used battery terminal wire brush tool that you can get at any auto parts store to do that. They generally sell for less than $10; one end cleans the battery terminals and the other cleans the cable connection to the battery. If you use a pocket knife, don't scrape too vigorously, because you take off too much of the metal.

I worked in an my dad's electrical repair shop for six years a long time ago. We got your type of problem on what are now old American cars with some regularity. The problem resulted from a bad solenoid, a bad battery or a discharged one, or from poor electrical connections. The electrical connection problem was most usually corrosion at the battery connections. It can look fairly good and still have corrosion. Also check the cable connection at the solenoid. Make sure it doesn't have corrosion and that it is fairly tight.

You may have the same problem if your buy a new starter since you've had it with the two different starters and solenoids you have had on the car.

I have done all of that. All connections are super clean and tight. The switch or plate inside the solenoid just randomly does not make a connection. This morning I tried to start the car after it sat all night and it started up perfectly. Drove it till it was fully warmed up, drove it on some rough spots to cause vibration, shut it off and it restarted perfectly. Shut it on and off several times and it started without fail every time.

For all I know it will never happen again! This problem is really getting on my nerves!

I'm trying to think that of any different tests to nail down the cause but it seems like swapping starters may be the only one left at this point.

I just checked pricing on genuine Bosch starters for my 1984 300DT. They are priced reasonably, under $180 for new and under $140 for reman. There may be a core charge, be sure and ask the supplier. If you value your time at a minimum of $50 per hour, you have far exceeded that price in terms of labor costs alone.

Where did you find new. I saw remaned Bosch at ********az. The car is actually a friend and he pays me. I already thought I had it fixed twice. Once after I replace the neutral safety switch and then after I put in this used starter. Both times it worked until he drove it for a few days.

That job was a bear. First time after owning four 617s. I've swapped and engine and a transmission but never had to mess with the starter.

Here is what the old starter solenoid contacts looked like. Do not know if this is normal or not. The plastic broke on the way out so I could get a look at them. It looks like copper transferred from the lug to the plate over time.

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