Been having intermittent issues with my starter and decided to attempt a rebuild.
Found a solenoid on eBay for pretty cheap but later realized that the part number did not match exactly what was on my starter -despite the part coming up for my 240D on multiple sites. Figured maybe the part number was superseded at some point or another...

Solenoids

The new solenoid had a slightly longer spring on the piston and a different anchor mechanism though both had a similar level of resistance.

I installed it and attempted a bench test.

When I apply 12v, the gear (bendix?) spins, but it does not move up and down. Isn't this the point of the solenoid? Otherwise, the brushes were good, the commutator (?) I scrubbed up with a nylon scouring pad to bring the brass color back, and everything else seemed to move freely.

I'm boggled. Ordered a rebuilt bosch unit from Napa just in case but jeez that feels like a waste... this seems like such a simple device (all magnetic field, and few moving parts).

What am I missing here?

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1981 240D 4sp manual. Ivory White.