What about a savage slipper assembly? Has anybody tried one of theses? Seems like this woud work fine:
http://cgi.ebay.com/HPI-SAVAGE-X-XL-...QQcmdZViewItem
My problem is this:
My motor "bottoms out" on the tranny case before the gears mesh together. I guess I could use like a 25T pinion


But I don't think that would mix well with the electronics. I was thinking that since the savage slipper also rides on a 5mm input shaft that it would be a fairly straight forward mod.