MTH Challenger This page is just various notes on things that are not easily found on the web. Slipping drivers / cracked wheel centers My friend had a problem with a bind on one of the trucks. Turns out the wheels are plastic centers on a splined shaft, and the splines are not large. The wheel had slipped a bit (about one spline) and that was enough to put a bind in the mechanism and it affected running. Realize that since only the rear driver is powered, that the connecting rods drive the other 2 drivers, and that clearances on the crankpins cannot be sloppy, and the drivers must be in quarter, or at least in synch with each other on each side. It was also found that the plastic center had a crack in it, right through. We could not tell if the crack caused the slippage, or slipping caused the crack. There are no spare parts for the Challenger, and a used driver was obtained. This also had a crack in it, but it was "hairline". According to Ray Manley (probably the foremost Authorized MTH repair person for the #1 gauge MTH), this is not uncommon, and he has seen cracking on Challenger drivers new in the box. My friend made 2 tools to hold the crankpins in alignment in order to press the new driver on in proper alignment. Be forewarned, the axles are 59 mm apart, and the crankpin diameters are different, the front 2 drivers are 5.5mm in diameter, and the driven driver 4.5mm. Just for reference, the axles are 7mm in diameter. Likewise, the hex head bolts on the front 2 drivers are a different size from the bolts on the "driven" or rear driver. Disassembly just a listing of screws when taking the challenger apart, this was removing the rear truck 3 screws on the weight on the rear truck, 12 mm small head 2 screws on the rear truck steam chests, 14 mm "washer head" 2 screws, the mount in front of the rear truck assembly, 17mm "washer head" 2 screws on the mount to the rear of the rear truck assembly, 13mm "washer head"