I finally got around to troubleshooting a dragging brake problem I've had from the beginning. This was an interesting one..
The symptom was that the plane would pull to one side pretty hard regardless of how much engine torque was applied. I got the plane up on two horses. One wheel would rotate relatively freely (like 1 or two fingers on the wheel could provide enough force to make it rotate), while the other would have a dragging brake (you need your entire hand on the wheel to give it enough force to rotate). The problem existed for only half of the rotation.. NOT throughout the entire rotation of the wheel.
I dug out my runout gauge and found that the good wheel/rotor had 0.005" runout, while the "bad" wheel/rotor had 0.030" of runout. I disassembled the wheel halves thinking perhaps I had a bit of debris that got sandwiched between something during assembly. Everything was clean.
I mounted the wheel's center hub/bearings and its rotor to the plane's axle. The problem still existed. I swapped rotors between the two wheels (attempt to confirm or rule out the rotor itself). The problem followed the wheel, not the rotor. I examined the wheel's center hub.. and found the issue. Apparently one of the three "spokes" of the center hub was machined down exactly 0.020" too much. I sandwiched a feeler gauge between the hub and rotor and re-measured the runout.. which was now 0.004". (see photo)
I usually attack problems as "what did I do wrong this time?" rather than a manufacturing problem.. so it took me a long time to get down to the root cause of the issue. I have a call out to Matco, but for now, the shim is working very good with greatly improved ground handling. The next time I put the plane up on horses, I'll most likely replace the hub (about $50 new from Matco)
Rob Carsey, North Brunswick NJ
RV-12iS (N713) / Completed 12/2020
ASEL, Glider, AGI/IGI, LSRM-I, FCC GROL