Finally---I Score an Optima Mid

[Basher67]

Rear diffs are hard to come by for sure. I got very lucky with this one since the diff and diff gear were still usable after a good cleanup. The other gears in the trans and the front diff are not as expensive, but are still not cheap by any means. Locating a rear diff and gear is not easy in my experience. If you are shopping for one, I would definitely consider paying more for one that you're certain these components are in good condition.

[XLR8]

Thanks for the quick reply Coelancanth and Basher67. So, 50+ for rear diff and 25+ for front – when you can find them. Are these Kyosho parts or are they aftermarket (perhaps Robinson, Thorp, or?). Is it typically the plastic crown gear or the internal bevel gears that are trashed? The top input gear is metal, like a Stealth, right? GoMachV says that failures are common so do we know what causes them to fail? Is it age, poor materials, lack of lubrication (wrong lubricant), dirt, abuse, etc? Also, does anyone know if Kyosho is planning to re-release this model – guess I should have asked that question first.

[Basher67]

In my case, The bottom belt cover was missing, which turned the belt into a conveyor for a bunch of dirt and small pebbles. Once the metal top gear gets chewed a little it destroys the middle gear and eventually the diff gear. The diff balls are easily replaced but there is no replaceable diff rings (they are part of the outdrives), so if they get too pitted or chewed up, you're probably going to need a whole rear diff assembly. Coelacanth is much more experienced with these than myself. I would defer to his expertise on this.

[XLR8]

Thanks Basher. I definitely need stop asking dumb questions and review the assembly manual - I thought they had bevel-gear diffs.

[GoMachV]

Mid was gear diff, Turbo Mid SE was ball diff. I’d have to search for the Custom and the other variants as we only got those in the USA

[XLR8]

Hey, thanks GoMachV. I'm looking at the manuals on Kyosho website right now. I wasn't aware there were so many variants. It's a whole different world, isn't it. Those gears appear to be 32dp and they're pretty narrow and since they drive all four wheels, they're likely under a lot of stress. Anyway, I'm really hoping someone with some history running these cars will tell us that provided the belt covers are maintained to keep debris out of the trans, the gear set will last.
When shopping for a car, it would be nice to know the condition of the gears before hitting the BIN. The trouble buying a used car off ebay is that you never really know what you have until you crack it open. Anyway, I've only just started looking so the right car will eventually come along. Thanks everyone for the valuable info. I hope I haven't hijacked the thread. I am keen to see Basher's car completed.

[GoMachV]

I have bought a lot of Mids in my day and have never found one with gears that were even what I would consider decent. I swear one step in the manual must have told people to insert small pebbles before the covers went on

[XLR8]

haha... Well, you're probably right.
Based upon the directions in the manuals, the belt covers were so well servo-taped and their seams glue-sealed that they probably would break apart during a tear-down and often were not replaced. Or at least the thought of needing to buy new covers might discourage any future disassembly and cleaning. Perhaps this why two of the cheaper but well-used cars I've seen on ebay don't include any of their covers. I would expect the gear sets in those cars are probably shot; sorta like running a nitro car without an air filter.
I found this in the Mid Custom Special instruction manual. As I understand the timeline for these models, the Custom Special was the final Optima Mid version (experts please correct me here). Maybe by this time, owners had learned the hard way how important it is to keep debris from entering though the belts and their complaints prompted Kyosho to include this note.

[Coelacanth]

That image almost reads like a disclaimer..."no matter how small a hole you have, this can cause the gears to break down...it's not OUR fault!"

When I did my mid-motor RWD conversion of the Turbo Optima Mid SE with my OptiMutt build, I totally sealed the rear gearbox. That's obviously not what I'm suggesting, but be sure to seal the Lexan belt guide covers, not just along the bottom edges, but all around where the covers surround the gearbox belt openings. I used silicone because it's more fool-proof; servo tape will dry out and pull up over time, and can't easily be applied around the belt openings. (This is for a runner; for a shelfer, none of this matters.)

[XLR8]

Hey Basher, any updates? Were you able to resolve the body issues and locate the proper color? You haven't posted anything on this project in nearly two weeks so I was just curious.

[Basher67]

I've been waiting for another body to show up in the mail. It takes a couple weeks for them to arrive usually. Should be any day now. I've been pretty busy and haven't looked into paint yet. I also need to address why the stock speed control isn't working properly. I'll update as soon as I get it all figured out.

[XLR8]

Cool! Are you planning to decal the body and, if so, what graphics set is appropriate to this particular variant? I buy my restoration bodies from TBG and decal sets from MCI Racing... also from Canada. Come to think of it, I also source my restoration decal sets for the vintage motorcycle projects from another company in Canada. Perhaps they have less stringent copyright/trademark infringement laws - I donno.

[Basher67]

I have the Turbo Optima Mid SE decal set from MCI. I've always been very happy with their products. I was doing a little research today on the yellow color for the paint and didn't come up with a definitive answer. Even if you go by the listed color from Kyosho, the paints are long out of production, with no references to currently available paints. I'm going to try a few different yellow paints on some test panels to see which one I like best.

[EvolutionRevolution]

In my case, The bottom belt cover was missing, which turned the belt into a conveyor for a bunch of dirt and small pebbles. Once the metal top gear gets chewed a little it destroys the middle gear and eventually the diff gear. The diff balls are easily replaced but there is no replaceable diff rings (they are part of the outdrives), so if they get too pitted or chewed up, you're probably going to need a whole rear diff assembly. Coelacanth is much more experienced with these than myself. I would defer to his expertise on this.

Later versions of the Mid diffs have separate diff rings, but of course they are hard to find...

[Basher67]

Got the new body from TGB yesterday. It is much better quality than the first one I got. This one has a more uniform thickness throughout and clear cutlines. This is the good quality I've come to expect from them. That last one I got must have been a fluke. Now I can finally finish this car.