Harsh N-D or D-N Shift

1. Improper vacuum signal to modulator or defective modulator.
2. Broken reverse servo cushion spring.
3. No. 5 check ball missing from control valve (harsh into reverse).
4. No. 6 check ball missing from control valve (harsh into drive).
5. Broken forward servo cushion spring.
6. Thermal element does not close when hot.