My 16 yr. old son was driving my baby and says he tried to downshift from 4th to 3rd. to turn a corner and heard a pop (only description), and when he let the cluth out there was nothing. It's a M45 gearbox. After playing with it I've found the shifter rod is moving in and out OK, and the cluth seems to be OK. With the car parked & engine running I can shift between 3rd & 4th without the clutch and nothing there. If I try to engage 1st or 2nd without clutch it refuses to go and instead of gear grind there is a quiet whinning noise. If I put clutch in, I can put it in 1st & second but nothing is there when the cluth is released. If I try to engage reverse it seems normal and grinds gears. If I clutch it the shifter will go into reverse but nothing there when releasing clutch. Any good ideas out there? I would appreciate others thoughts before I pull transmission. Thanks.