TOPIC:

Hello. I am very new to building a Tamiya. I recently built a reissue frog and upgraded to a sport tuned 540. Upon doing so after an hour my gear box slips now. I opened up everything and nothing is damaged. 

Any suggestions?

Motor pinion is unscrewed, or diff outers are worn and sliping teeth in teeth.

It is a common issue with these gear boxes, The first thing you can try is adding shims between the MD9 gear and the bearing to apply more pressure the the diff assembly. The other option is to buy the MIP ball diff which completely eliminate the issue all together 

www.miponline.c...yword=frog

The usual thing is torque forces the diff to expand, which bends the aluminium gearbox sides. They don't spring back & the diff slips/clicks ... there have been lots of other fixes over the years, most are some sort of brace/clip for the gearbox sides, another was drilling one gearbox outdrive & tapping the other - then holding the two a set distance apart with a threadlocked screw.