When I am driving above 45 mph after a short time the car starts shuddering and the steering wheel starts jigging about. New tyres and wheels on the front to solve problem but is unchanged. So far I have checked all the arms and the drive shafts are okay. I have a feeling it may be the front diff. Any ideas? I put it up onto a car lift and at low speeds all the wheels turn bar the front ns. this seems to start to turn and then stop. this wheels will spin at speed but won't at 20mph. Has anyone had anything similar?