Maytag not cleaning

I think that my dish washer is not putting out enuf pressure. Water sprays out of the spray arms, but they don’t spin. I have removed and cleaned the screen and filter. But no change. I am looking for a manual for teardown and trouble shooting. Since it drains fine impellers are probably ok. But I am not shure about any seals. Looking threw the parts manual here the seal has been updated. Now how to get to it? Any help is greatly appreciated.
thanx

Dustin

Here are your parts
http://www.appliancepartspros.com/partsearch/modelsearch.aspx?model=MDB7100AWB

Here is a service manual. Not the same as yours exactly but the pump looks the same.
http://www.servicematters.com/maytag_library/docs/16010622.pdf

Thanks the information help me find my problem. the discharge housing has a plate cast into the bottom. It broke off and was spinning around the housing slowing water flow till it wore a hole in the side of the housing causing pressure loss. I am ordering parts and should have a brand new 9 year old dishwasher.
Thanks Again,
Dustin