We have constantly been dealing with this dishwasher since we bought the house. The dishes are always gritty, and don't seem to be rinsed well. I have never seen the middle or upper spray arms spinning. The water rises in the rear tube but only about half way. I've cleaned the screens and filters. Checked the ball check valve. removed the electric motor and attached power to it and it runs. The impeller is tight on the shaft and not stuck. The tubes are clear.
I haven't figured out what makes the ball shift to direct the water to the upper arms, possibly thats the problem. Any suggestions or troubleshooting procedures would be appreciated.

Thanks for responding Tim, I did as you said and quickly unlatched and latched the door. I see the water going up to top pipe and supplying water to the upper nozzle. I tried this a few times plus tried to see if the arm was spraying but it isn't. I checked the tube where the arm attaches and its clear. I watched it carefully this last time and throughout the cycles water does go up to the top arm but never do see it spinning or spraying.
The water temp is very high. I don't think its a problem with hard water as in our area hard water will etch the glasses. This grit is more like food that hasn't left the dishwasher and dried on the dishes. We use a liquid soap. We've tried others with no changes.
The hot water tank is only about 2 years old. Same age as the house and dishwasher.
I'm wondering now if there isn't enough pressure for the upper spray arms, or maybe the drain pipe is partly plugged...
I'm hearing this dishwasher doesn't have too good a reputation

Same problem here. I have the FDB635RBS0 model dishwasher. Looks like I was lucky - it lasted for 7 years.

Water works its way up the plastic tube running on the outside body of the dishwasher, but the volume is real low and as a result the top arm does not spin. Started noticing detergent residue on cups and plates found on the upper rack.

I added one extra gallon of water to test for water fill issues and still no spin on the top arm.

I pulled the dishwasher from the counter (removed two braket screws), shutoff the water, unplugged, unhooked the water supply and drain supply, removed the bracket holding the motor and simply pulled the motor out. It was real easy getting the motor out.

I used a digital multimeter to check the resistance of the motor leads and got no indication that any current was passing between the leads. Additionally, when I turn the impeller there is resistance and then suddenly it turns as if it is spring loaded (this repeats as I turn it). I am not sure if this is additional evidence for a bad motor or if this is how it sends water to the top of the unit and bottom as discussed earlier. After the repair, I'll let you know how it turned out.

Thanks for the discussion.