I have a 35-yr-old 6-speed recreational bike (actually 2 of them). One works fine, but one will only allow me to turn the pedal and wheel several cranks (go maybe 4-5 feet), then jam. I've compared the 2 bikes as closely as the untrained eye can and can't see a difference. Any suggestions? It not the hand brake... checked that closely already. I hate to take it in for repairs, and I hate to scrap it without trying this forum. Thanks.