I've had problems with the coil stops in the PBR Bally regular (non-linear) kits--they don't hold the flipper up when ball hits (you get that double bounce when the ball hits the flipper). I replaced them with non-kit ones from another vendor and it solved the problem. I don't know if they are still selling the bad ones in the kits -- this was a few years ago.

I kept the bad 'kit' ones for other coils. They work fine for non-flipper coils.

That's not true. If the stop does not seat well, the hold is affected. There's something wrong with the PBR kit stops (unless they've fixed them by now). They don't hold the flipper as strong as the non-kit stops. It's not a coil issue. Maybe there is something different in the finish or design of the stop (causing it to not seat firmly to the plunger) or the alloy used in the stop.

On the left is a non-kit stop--these provide a good, firm flipper hold.

On the right is the kit stop that does not hold the flipper adequately against a ball drop. You'll notice the concentric ring on the right stop. This may be the source of the problem, the smaller surface area, results in a weak flipper hold. Or, maybe the outer ring is not level with the inner ring, causing a weak/uneven seat. Or it could be something completely different, but in use, these stops simply do not hold. If you push down on the flipper while in hold position, you can easily break the hold--whereas it is very difficult to break the hold with the stop on the left.

If you get these stops in a kit (right picture), I'd recommend you avoid using these stops for flippers. Save them for non-flipper coils.

coilstops.jpg

It makes sense from a physics standpoint, though.

<geek mode>
Magnetism follows the inverse square law. Basically, when there is a small decrease in surface area or increased distance between the two "magnets" (for example, a bad seat between the stop and plunger), there is a great reduction in magnetic field strength.
</geek mode>

In my machines, nothing else solved the issue. The problem was 100% due to the coil stops pictured on the right in my post above (the silver bracketed coil stop with the concentric circle on the stop would not provide adequate hold strength against a falling pinball).

I hope this does not happen to anyone else, and maybe it was something peculiar to my games, but I wanted to post the solution that worked for me, in case someone else has the same issue.

If you replaced the stop with something non-ferrous, the flipper would fall easily once the coil has switched to low-current.

The coil induces magnetism in the plunger, and the coil stop. The magnetic attraction between the plunger and stop is what holds the flipper up in low current mode -- not the power of the coil. You have to remember, at this point, the flipper coil is running very low, holding current -- barely enough to pull the plunger into the coil, and not enough to hold it there firmly.

If you've ever had an EOS switch go bad, you'd see that the flipper can barely pull up against the force of the spring. If the plunger were resting against a plastic stop, you could easily pull it down with your hand. The low-current force of the coil is not enough to hold the plunger firmly inside the coil.

If you still don't understand, you can try an experiment for yourself. Push down on your flipper without changing anything. Then push down on it with a small piece of plastic separating the stop and the plunger. (disable your EOS if you do this experiment) You'll notice a big drop in holding force. The thicker the plastic, the less holding force you'll notice.

The stop and plunger are together when the flipper is up. You can visualize it as a bar magnet holding a chunk of metal. When you let go of the flipper button, its like you 'turned off' the bar magnet and the the chunk of metal falls away from the magnet.