I have a raleigh technium from the late 80's that I'm trying to make into a commuter it has a suntour RD and DT shifters I went to the LBS for a new wheel. They sold me a sunrims m13II and a shimano 6 speed cassette. I can use the shimano with the the shifters in friction mode. My problem is the rim keeps slipping on the frame and twist until it hits the brakes. The QR is as tight as I can clamp it but it still slips. everything looks right to my nonprofessional eyes. any ideas ?