TOPIC:

I've just bought a vintage monster beetle, and am in the process of replacing the gearbox. I've heard that the gearboxes are weak, and i'll be fitting new bearings, an upgraded motor (21 or 23 turn), and electric speed controller. Does anyone know if there is an option out there to replace the stock gearbox with alloy parts? Does anyone have a list of parts that i would need, and could suggest where to get them or post up a link?
Many thanks. I am a newcommer to vintage rc, so sorry if this sounds like a stupid question.
Andrew.

Not a stupid question at all. Yes, the original Monster Beetle gearbox is not known for its durability. As you noted bearings are a must. Much of the MB gearbox problems lie with the stamped alloy side plates. Under strain, they flex outward allowing the differential gears to separate and skip over each other. The tiny alloy diff gears are quickly damaged if this occurs repeatedly. There are two "fixes" for this :search for the "Oldfrogshot" screw mod on Tamiyaclub. This involves tapping one of the diff outdrives and then using a tiny screw to tie the diff outdrives together to prevent separation. The other method is to just shim the backside of the diff gears with washer(s) to keep things tight. Be careful not to overshim it or binding may result.

The other issue with the MB concerns the outdrives and half shafts themselves. Under greater power the hex ends can round off and create futher slippage. This fix is easy. Replace the old hex headed asseambly with proper "dogbone" half shafts from the re-release Frog. They fit right in with no modification.

Lastly, you could replace everything with RR or Thorp hardware (ball diff and dogbones, etc.) but these parts are now rare and pricey. Good luck!

Thanks. I've already ordered a re release frog dogbone system, and i'll try the 2 other mods to the gearbox. When screwing the diff outdrives, should they be as tight as possible to prevent any movement?

No, don't make it too tight. The screw installs much like a ball diff adjustment screw (same basic location) but serves a different purpose. A ball diff screw must put tension on the diff balls to prevent slippage between the diff balls and rings. Oldfrogshot's screw mod is there only to prevent the gears from skipping teeth. Make it just tight enough to prevent the teeth from skipping but loose enough to allow the diff gears to rotate freely. Too tight will essentially lock the diff and that would be detrimental to handling.