Kenmore washer won't stop spinning

I am having trouble with a Kenmore washing machine model 417.43042200 Serial XC25122964 (front

loading; mechanical timer/clock. (It is on the bottom, stacked under a drier).
When the washer reaches the final spin cycle the timer stops moving and the spin continues, presumably

forever or until I manually stop it by pushing the main switch or advancing the timer manually.
At first I thought the timer was bad but the same thing happens in another wash cycle using a different section

of the timer.
My guess (with limited experience in these things) is that when the final spin cycle is reached, electric power is

suspended from the timer until some other sensor senses that the spin has achieved its purpose and it sends

power back to the timer to advance past the spin cycle and complete the wash. I think that sensor is faulty.
Any help you can offer about what that sensor would be and where I would find it (also how hard and

expensive it is to replace) would be greatly appreciated.

Stu
chartman1@adelphia.net

It may also be the load is off balanced or the water is not draining completely. If either of these occure the washer will not go into high spin thus will keep spinning at a lower rotation.

Thanks, Liberty.
The problem occurred even with no laundry load in the machine. The water drained completely and it went into high spin. Actually, I think (visually and from the sound made) it went into a higher spin speed than was called for by the Final Spin Speed switch setting (Normal, out of Slow, Norman and Fast options).
I am getting convinced that the problem is in the motor speed control board and I will do some electrical testing when I get time.

Stu