Just an FYI, here is an amazing
breakdown video for doing the gears. Not sure if this guy is a member here but this is the video I will have playing on repeat when I do the gear replacements.
This is a good video to use as a reference. Thanks for posting the link!
He moves very fast in the video. Take your time. The video does a great job of showing the order of disassembly and reassembly.
Here are some tips for replacing the gears:
I do recommend removing the control panel from the game and taking it to a work bench or table to replace the gears.
Always replace the gears in sets. While it may be tempting to only replace a single cracked gear, mixing the plastic and brass gears is not recommended. I actually tested the combination of a brass gear B together with a NOS gear A to see what would happen. Although the gears did mesh well and worked, after a short time I observed that small amounts of nylon "dust" or small particles were appearing even when the gears were lubricated. This is an indication that the brass gear was causing rapid wear of the plastic NOS gear. While it is more work to replace gear A, go ahead and replace the pair. This is also applies to gears C and D. Fortunately it's much easier to replace the two smaller gears.
The replacement gears will fit snug on the original shafts. The NOS gears also fit snug. This is by design. If you are having trouble fitting a gear onto the shaft, check that there are not any burrs on the shaft or the keys. If you do find a burr or nick, you can probably clean it up with a file and emery cloth. Also make sure the keys are fully seated in the groove of the shaft. If there is any dirt in the notch, clean it out.
It is best practice to clean up any old lubrication while you have everything apart. Apply new lubrication sparingly to the gears where the teeth mesh together. You don't need a lot of lubrication. A thin film is all that is necessary. See the photo posted earlier in this thread by Mylstar for an example. I recommend either Nyogel or Super Lube Synthetic Grease (links below.) I don't recommend automotive or industrial grease as they are too thick for this application. You also need to add lubrication on other moving parts like the slide bolts and plate, and motor link bushings, etc.
You will notice a red thread lock on most of the fasteners from the factory. This is to keep screws from working loose due to vibration. Honestly, in a home use environment, it's probably not necessary to replace this. Just tighten all the fasteners and the lock washers should hold. If you decide you want to replace the thread lock (a good idea for commercial use), then use Loctite 290 Green Threadlocker. This is medium strength and designed to be applied after assembly. It only takes a small drop on each screw. Don't use the red threadlocker. It is for permanent assembly and even though the color is the same as the original, it's not the same type of threadlocker that was used by Sega.
Depending on what type of steering potentiometer you have installed on your game, there may or may not be a flat side on the shaft. If there is a flat side, install gear D so that the two set screws do not align with the flat side. The set screws will be too short to reach the flat side of the shaft and tighten down properly. Rotate the shaft of the potentiometer so it is mechanically centered before installing the bracket back onto the control panel. Once everything is fully assembled, turn the game on and go to the diagnostic input test screen. With the steering wheel centered, try to adjust the steering pot so you have 80H shown on the screen. Actually anything between 7CH and 84H will work fine.
Good luck and let me know if you have any questions.
Links to products mentioned above:
Nyogel
Nyogel 779 was a common lube used by Atari on most input assemblies. Manufacturer Name: No Manufacturer
arcadefixit.com
Super Lube
Loctite Green