Bottom part of agitator does not work, i replaced the clutch dogs two weeks ago for the top part. kenmore series 80

This assumes that you have a basic Kenmore / Whirlpool top load, direct drive, neutral drain (it doesn't spin until the pump removes most of the water) machine.

First, see the Sears parts site for your washer:
http://www.searspartsdirect.com/partsdirect/index.action

Enter your model number and you'll see a list of major sub-components with diagrams and parts.

There are a number of Series 80 design washers. You'll need the actual model number to better check for the problem.

First, I'd remove the top agitator (as you've already done), then I'd remove the main agitator.

Under it you will see a clip and what Whirlpool calls a "washer". The "washer has two prongs, one fits into the main agitator shaft drive and the other fits in the lower agitator. If one or the other of the prongs is broken, the agitator most likely wont. I'd also look inside the main agitator to see if the ridges are broken off.

I'd then start the washer on it's smallest cycle and see if the main agitator shaft turns back and forth. If it doesn't and the washer goes through it's drain and spin cycles, the problem is likely in the transmission itself with what they call the agitate gear and / or agitate cams.

Please see the Whirlpool / Kenmore PDF document on installation, maintenance and operation of direct drive washers.

https://secured.whirlpool.com/Service/SrvTechAdm.nsf/2cd44500d572193285256a45004fd9d6?OpenView&Start=1

This is a Whirlpool document with parts lists for their commercial washers (basically the same as the consumer models)

If the problem is in the transmission, although it looks complicated, it really isn't that bad if you have a moderate level of mechanical ability.