Here is some information about the Bally Zipper mechanism. This is mainly for EM games. The SS Bally Medusa uses a very similar mechanism except Bally adapted a drop target coil for the 'close coil' instead of the custom square coil that is impossible to find.

A few basic notes:
1) The Zipper should be dry. No lube is necessary. I like to put a very small amount of lube on the slide (annotated in the photo below) and a tiny drop of 3in1 oil where the return spring attaches at either end. This is my personal preference. Everything else should be DRY. The best thing to do to a Zipper mechanism is remove it, strip it down and clean it. Most have oil, grease and tons of coil dust jammed in all the parts. CLEAN IT!
2) There were a few types of close coils used throughout the years. I'm not listing them here because each schematic calls out the coil used for the game. The square coil is a standard size and available today. However, the resistance and current from the original games are not available as new parts. The original coils were very low resistance and pull quite a bit of current. This is how the speed and force was generated to pull the heavy assembly closed. Many coils burnt up because 1) the switches were out of alignment and 2) the coils were not fused. If you have a game with a Zipper mechanism, please add a fuse to the close coil. You could add a 1 Amp Slow-Blow or a 1.5 Amp Slow-Blow for proctection.
3) The wings that hold the flipper coils have a lot of mechanical wear from 50+ years of operation. There is not much you can do to restore time. I have found that if you double the small nylon bushings under the wings in the guide help remove a lot of the flipper vertical play. This prevents flipper drag when the whole assembly is installed.

Parts that have been sourced for the Zipper mechanicals:
1) Large Nylon bushing size: 1.000" x 3/8" x 1/32" [Available from Superior Washer & Gasket]
2) Small Nylon bushing size: 5/8" x 5/16 x 1/32" [Available from Superior Washer & Gasket]
3) Nyliners are for a 1/4" shaft and a 5/16" bore [Available from your pinball parts supplier of choice]
4) Flipper rebuild kits [Available from your pinball parts supplier of choice]

Superior Washer & Gasket does not have specific part numbers for the Nylon bushings. They are ordered by the dimensions listed above. Their phone number is 631-273-8282.

Photos, annotations and diagrams below. Photos provided by Pinsider Garrett Diagrams pulled from online parts manuals.

Zipper Flipper 1969 (resized).png

Zipper Flipper 1976 (resized).png

Zipper Full Assembly (resized).jpeg

Zipper Breakdown (resized).jpg

Zipper Large Washer 1 (resized).jpeg

Zipper Large Washer 2 (resized).jpeg

Zipper Small Bushing (resized).jpg

Zipper Washers & Hardware (resized).jpg

I also worked with a few companies to see if I could source a replacement spring. No luck. It would have to be custom wound and thousands would have to be fabricated. Hopefully your spring is not compromised. The spring tension and properties are based on diameter of metal used, number of turns and tightness (diameter) of the turn.

Hi Garrett. Happy to help and thanks again for the photos.

To this day, every Ace, True Value and other hardware stores...I stop and look at the springs in the hardware drawers. I have never really found anything close. But I always look. I like your idea of the screen door spring. I did try a stock sample from Century Spring in Commerce, California a few years ago because they had something close. But the tension was way too tight unfortunately.

Officially a Sticky! Hope others find this info helpful.

Yes. Follow the sticky thread about the Zipper mechanism. PM if you ha e any questions.