I ended up keeping my TC3, got a new radio for it and the aluminum driveshaft, nothing special, but its running great. I can't say the same for my roommates car. He just picked up the TC4 and we set it up yesterday, we followed the instructions for assembly but when we put the motor, radio and speed control in there was a problem. The motor is working the shaft is spinning but the car doesn't move. If we pick it up the wheels start to spin, but the second we put it back on the floor it doesn't move at all. What could be the problem???

It sounds like your diffs are not working, take the diffs back out of the car make sure you put them together right, and then go from there,

do you notice any of the drive train parts rotating when on the ground?

either you forgot to put in the axle pin for the wheel hexes or its the diff too loose or assembled incorrectly. when you put the car on the ground are the axles spinning. if not then its your diffs. if the axles are spinning when the car is on the ground then check the wheel hexes and pins.

sounds like my problem i had, check to see if one of the push pins came out of the center shaft cup near the spur gear.

Did you figure out the problem Yet?

thanks guys. . . I took the diffs apart and it seemed that I didn't tighten them enough. I just tightened them a little and now its working fine.

With a TC4 you'll be getting used to working on the diffs soon.