Starter Life
 

And therein lies the rub :

Many (? most ?) don't take the time and effort to maintain their vehicles so the starter only runs a second or two, tjis of course means it gets hot and so wears faster....

I see then grinding away and wonder why ? .

Zoom Spout oil is an excellent oil for bearings/bushings. It's light enough to impregnate the pores in the bearing and saturate the wicking (if it has any) but heavy enough and with enough paraffin content to maintain a lubricating layer on the surface of the bearing.

Hmmm, solenoid too?

My starter does a chirp (and doesn't turn over) roughly every 20 times I crank.
But it used to be every 50 times, then 40, etc.

I'm not sure what causes that sound... would love not to throw parts at it, but something is definitely up down there. Brushes and a cleaning were as far as I had gotten.

What are the symptoms of a failing solenoid? Or even brushes for that matter?

Sometimes a worn starter ring gear or starter pinion gear will cause this. Engines tend to stop on a compression stroke and as a result tend to chew ring gears in specific locations. A 4 cyl will have 2, a 6 will have 3 and 8 will have 4. Rotate the engine and inspect the ring gear.

All cars and especially older neglected cars maintenance wise really benefit from a serious maintenance run. For example I wish I had a dollar for every year all the door hinges on all of the old 123s have never seen a shot of grease. It speaks volumes for the design of those door hinges that we are not dealing with serious wear issues with them now.

Neglect in oiling the hood hinges is another favorite. It can become a repair job I was not thrilled with when one side broke out at the very back point.

Dry window regulator systems probably cost motors. Periodic lubrication of the window channels as well should not be neglected. The list goes on and on.

The throttle linkages are actually designed for periodic attention but get little in the majority of cases. This is easy stuff to do and you build up a variety of lubricants over time. Neglecting to lubricate the sunroof is not a good ideal either. You do the cable as well.

It may or may not be in the mind. Knowing that you have attended to all the 30 to 40year old places and got them lubricated again. It makes the car feel better to you usually.

Perhaps it is a form of bonding as well. In the process you probably also learn more about lubricants and their specific applications. I know I have a shelf full of all types of specific lubricants and do not have them all. Even door and ignition locks get ignored all too often.

I just got through explaining to the wife that the keys hanging off the end of her ignition key case. Are hard on the the ignition key tumbler because of the leverage. On her new used car. Did it work? No.

I was then on the verge of explaining this had also killed a lot of people with GM cars. When the first discussion did not work. Then decided it was too early this morning to be reminded the car was not their product.

Is this a gear that's part of the starter? Or the gear that's part of the engine?
Having a little difficultly with terminology...

The ring gear is usually heat shrunk to the flywheel or a part of the flexplate. They have historically been changeable on flywheels.

Zoom Spout Oiler
 

Thanx ~ I've been using it when I service HVAC blowers already .

No problem, sometimes there are many terms for a particular part.

The large diameter gear that tends to wear in a couple of specific spots is the ring gear / flywheel gear ( on a manual trans car ) / Flex plate ( many auto trans cars ) / starter ring gear ( not part of the actual starter motor )

This ring gear is generally replacable on a manual trans car. Race cars tend to have the teeth cut directly into the flywheel. The ring gear on an auto trans flex plate is welded to the flex plate and generally replaced as an assembly

The small gear that meshes with the above gear is a starter motor pinion gear / starter drive / " Bendix " ( an old brand name applied like Kleenex / Band Aid / Xerox )

Fortunately ring gear wear failure on this vintage of diesel Mercedes is very uncommon. Even though by now many have exceeded their design requirements and expectations. I never remember a case posted. Flexplate failures do fail on them sometimes though.

Seems then I have a flywheel gear (i.e. manual trans).

This is beginning to sound like a large service item...

In order of operations, I take it removing the starter for a
1.) cleaning/re-oiling
2.) replacement of brushes
3.) possibly the commutator end bushing
4.) solenoid
5.) check flywheel gear and or starter bendix for missing teeth.

Your issue sounds more like the yoke binding or the pinion gear/bendix seizing on the shaft instead of sliding freely.

A failing solenoid typically makes the "clunk" but nothing else happens. No starter motor operation at all.

Worn/failing brushes typically does nothing at all unless you whack the motor with a hammer. The solenoid grounds through the brushes, so if they don't make contact with the commutator then the solenoid has no ground path and won't pull in.

The old Presolite starter on our test generator at work does what yours is doing from time to time. It was the pinion/bendix assembly sticking on the shaft and failing to engage the ring gear. We tore it down and repaired it several times, but once they gall the metal you're kinda screwed. Finally opted for a rebuilt and never had a problem since.

Thanks for that - found a solenoid for $10, brushes for about the same.
Worth a shot before anything more drastic.