my wife owns a 1984 bmw 633csi with manual 5 speed, it sat for approx 6 months, she went to drive the car and found that she cannot shift into any gear while the engine is running, it will shift if the engine is off, why? It ran fine before she parked it.
Did you check the hydraulic clutch fluid? Sounds like you have a failure in the clutch master or slave cylinder. Make sure the clutch fluid resevoir is full then pump the clutch pedal rapidly and see if it will go into gear.
dartman69 thank you kindly for the advice concerning the clutch pumping, it worked like a charm.
I am glad that worked. I am concerned that you might have a small leak in the hydraulic system. How was the fluid level? You might want to look under the vehicle for any signs of leaking.
Sometimes, the clutch disc just sticks to the flywheel. BMW motorcycles are famous for it.