Quoted from Desmodromic:Some have mentioned having loose coil stops. Definitely worth checking but note that it's easy (like most fasteners in Pinball) to over-tighten and strip out the receiving part, so don't over-tighten!
We noticed some funky behavior here last night when trying to stop/trap a ball with the left flipper. The flipper would "dip" when the ball hit it and with the glass off, you could easily confirm that when held up, the flipper itself could be pushed down even with the coil engaged. Turns out in my case, I had a bad coil stop. The insert looks like it was never really struck to mushroom over the end and firmly attach it to the bracket. Pics tell the story. I had a number of PBL coil stops handy so I just swapped it out and back in business. The coil stop on the right flipper is fine. I pulled and inspected it, but it's properly riveted and looks identical to the replacements I got from PBL so I reinstalled and will keep using the original on that side until it wears or loosens up.
You can see the failure to flatten the end of the pin here:
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In my case, the insert was free from the stop by the time it was noted and came out in pieces.
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Stern's Coil Stops have sucked for ages. It's one of the first things I change out along with the rubbers.
Really wish they would just fix this as it's extremely noticeable and makes a huge difference on location games.