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I was given a Kyosho EP Ultima ST roller in rough shape. It is missing some parts but the main issue is the differential. It is chewed up internally and needs the gears replaced. I found the manual on line but it doesn't have parts numbers. Would OT28 be correct or fit? I picked up some new shocks from Dollar Hobbyz for a decent price but need some bearings and a body to get it where I want it. I don't want to spend more money on it until I find a replacement differential or new gears.

On another note, has any one ever had a tire go rock hard? Three out of four tires are pliable but the forth?

Thanks for any help

Yes, OT-28 will be compatible. If you want stronger parts than those, try to find FZW-13, they are proper steel gears. For those 2 other small gears, the updated gear is FZW-15.

You should check out my thingiverse page for 3D printable Ultima ST parts:

https://www.thingiverse.com/jiipeee/designs

I just released an upgrade set for Ultima ST. You can swap the whole transmission to RB6 and use todays parts with it. For EP Racing Sports im not 100% sure if you need to drill two new holes to the chassis, as the chassis differs from the Type-R that i have, but if you dont want to drill your chassis, you can print my Type-R main chassis.

Thanks for letting me know. I will be looking for the FZW-13. There is some really cool stuff on your site that I am sure I will be using. I have the site bookmarked, thanks for providing that as well. Would have said so sooner but life got in the way.

Yea, the most future proof upgrade would be swapping the whole transmission to RB5/RB6 rear motor transmission. But for that you need RB5 main chassis and RB5/RT5 rear chassis plate and the whole RB5 transmission.

RT5 main chassis is also a possibility, but its 10mm longer than Ultima ST Type-R. I dont know how long the RB5 chassis is.

I´ve now fiddled around with Ultima ST Racing Sports GP, Ultima ST Type-R EP, Ultima RT5, Ultima RB5 and Ultima SC6 parts. For the EP version of the car, if you print/get the RB5/RT5 main chassis, you are future proof.

You can example swap the whole front end of RT5 to Ultima ST EP chassis. I´ve tested it and it works. You can build an SC or RB from that chassis as well. Imagination is the limit.

With RB5 rear chassis plate and my parts, you can use RT5/RT6/SC6 rear lower suspension arms. You can build anything out from that chassis. I have 3D printed basically the whole ST car and driven it during winter and now summer without any problems.

I now see why Chinese copied this chassis so much with their Turnigy SCT and Quanum E-Guana and why Robitronic did their Stadium Truck like they did. The chinese did the most obvious copy. Just google Turnigy SCT and look at it.

People are already using my designs and selling the parts in ebay. I even contacted one guy that sold rear shock towers and asked them to remove their listing as it violates the licence, but he just printed even more parts with different colours to sell. So i might remove my parts from thingiverse. Just saying this so download what you need, they might be gone in some day.