I have taken my bagless dirt devil turbo apart many times, and have thoroughly cleaned it , but it still doesn't want to pick up dirt on carpet. Drops back at least half of what it picks up

Has the hose at the clearer head gotten clogged with carpet fibers, that is the common reason for this.

Mate I just googled Dust Devil UD40180 repair manual and found this link, I hope it helps... If not then you google Dust Devil UD40180 repair manual It might give you some ideas...CHEERS
http://www.ereplacementparts.com/dirt-devil-ud40180-ultra-vision-turbo-bagless-upright-vacuum-parts-c-36976_37103_37186.html

I have a Dyson and was having a similar problem some time back. I found out these bagless systems still have a filter that picks up the fine dust to keep it contained. Find out where yours is located and beat the dust out of it really good or just replace it.
Hope this helps.

it might be the roller its self

normally, the vacum has a height adjuuster. try turning it to higher level

Hi,
Here is a tip that I wrote about my Bissel but I bet you have the same problem and the hose is clogged...

Bissell Bagless Upright Vacuum not working
http://www.fixya.com/support/r4387950-bissell_bagless_upright_vacuum_not

heatman101

It's probably not picking up because the belt is worn and stretched. With a new belt it will pick up a lot better. Here is the belts you need:

Dirt Devil FeatherLite Belt

I called Dirt Devil and they said return it!

That means that your belt is worn, stretched or broken. You need to replace the belt. You can get replacement belts and view the manual:

Dirt Devil Dynamite M084600 Belts

Download the Manual (PDF)

Here is a link to the belts you need and to the manual which has instructions:

Dirt Devil Vision Turbo Replacement Belts

Download the Manual (PDF)