During final spin cycle a code that says DC of balance load and there is a bang from the tube

Off balance causes: What to Do if Washer Is Off Balance During the Spin Cycle With Every Load

http://www.partselect.com/Repair/Washer/Shakes-Moves

Most likely tub bearings and spider gear are bad.

Something is causing the drum to be way out of balance. Does it bang and make noise when it's spinning empty? Probably not. Is something stuck on the side (inside of course) of the drum, causing it to shake when spinning? If not, a spring or shock absorber (connecting drum to sides, bottom or top of machine) has broken or come loose.

Lift off the top cover and make sure that the supports are connected http://www.appliancepartspros.com/top-cabinet-parts-for-whirlpool-wtw6600sw2.html

To detect excessive wash tub movement and shut down the wash cycle. Here is a copy of my post from a real DIY forum;

Google this Neptune TL Washer FAV6800AWW 5 post down.

Here ya go.....in this post I discuss the issue related to unbalance error codes DC and UC;

Your FAV6800A or FAV9800A is going off balance with DC or UC unbalance error codes during spin cycle and you see/hear the wash tub banging around at the start of Spin Cycle of the wash cycle or a Spin Only cycle. If this is the condition the TDS (Tub Displacement Sensor) is working as designed and signaling the Control Board properly of an unbalance wash load condition.

The Control Board receives a varying D.C . Voltage from the TDS sensor and if the out of range D.C. Voltage limit continues the Control Board will halt the Spin Cycle and try to redistribute the wash load. If you are interested I will show you how to monitor the TDS input to the Control Board with a DVM.

The Control Board then starts the Spin Cycle again. If the wash tub/basket out of balance condition continues the Control Board will attempt another redistribute of the wash load. After several attempts (4 to 5 I believe) the Control Board will shut down the Spin Cycle and send a error code DC or UC to the LED display of the FAV6800A, my machine type. And I believe a text statement to the LCD screen of the FAV9800A machine i.e. something like "Unbalance Condition" I'm not sure what the text message is.

If you need help open a post in that repair forum and I will try help you through your issue.
The forum is free and my time is free I just don

If your FAV6800A or FAV9800A wash tub is banging around in Spin Cycle of the Wash Cycle and your Control Board signals a dC or uC error code to the console I feel you have a Clutch malfunction. I feel the TDS is working as designed with the unblance error code shut down.
See my Clutch Fix post for more info related to dC and uC unbalance errors with the FAV6800A and FAV9800A TL’s and the repair action…….Rich

sounds like drum is out of balanced call repairman they can rebalance drum this needs to be done ,once a year.

old duets have nut on rear pulley that becomes loose. remove rear panel and tighten nut. check while spinning by hand if pop is felt. if it rotates smoothly then you may need new shocks on tub

please balance your washer and use smaller loads

make sure all shipping pins are out the tub should move all around from side to side if it level still bangs its eather the balance ring top basket are there 3 slides on a plate above the motor just put some silacone oil on tham move around