10 spd levers work with 9 speed derailleur
 

I have a full group of DA 9 spd but I can't get my lever to let the cable go so it shifts down to the little ring. I spray the whole can of WD40 this afternoon. If I have to get a set of shifters, they will be 10 speed shifters. Will it work with the 9 spd derailleur along with the 9 spd cassette? How about 10 spd cassette?

since spraying is not getting the de gunking job done,
pull the lever off maybe the plastic-rubber hood too, and soak it in some solvent..

probably must have both cassette and lever same speed number, but ,
cassette driver, part of the hub, may be different.. 9>10.

Since you are in LA, ask at a bike shop that caters to high end race bike users.
probably a dozen in the Metro area..

as below, step 1 is check dropout hanger alignment on the frame..

So are you saying that when you downshift, the chain won't fall to the smallest gear? If that is the case, has the derailleur been bent by having the bike dropped on the drive side which could have knocked the derailleur out of whack? If everything else seems normal and there was no impact, then what I would do is try loosening the screw gently corresponding to the small gear in question (H for the rear derailleur, L for the front derailleur). That might allow the derailleur to drop all the way to its loosest position. Don't over loosen or the chain will drop off the gears altogether. If it still isn't working right, you might have to release the cable hold down for the derailleur in question to make sure that it isn't a cable problem. If after you loosen the cable stop, try downshifting and seeing if the shifter will downshift all the way down to its lowest point.

Check the cable housing for kinks or possible deterioration in housing and resulting collapse of housing.

10 speed shifters with a 9 speed cassette won't work right.

But 10 speed shifters, a 10 speed cassette, and a 10 speed chain- those three things, and you're good to go.

10-speed shifters will work with 9-speed derailleurs and chainrings and cassettes just fine when you use the alternate cable routing to the rear derailleur. See: http://www.ctc.org.uk/desktopdefault.aspx?tabid=3946 and http://sheldonbrown.com/derailer-adjustment.html

I've been doing it for about a year now, using a 9-speed Ultegra drivetrain and 10-speed Microshift shifters. I just make sure the last click is disabled by the inner limit screw on the derailleur to keep the derailleur from going into the spokes!

Then, when you want to buy a new chain and cassette, you can convert to 10-speed any time in the future, changing back to the normal cable routing.

But you might just need adjustment-- Can you get the shifter to click 8 times just pulling on the cable by hand? If so, then it's probably just time to adjust everything, and not bother with the 10-speed replacement yet.

simple enough. 9 spd derailleur is fine with that combo?

hanger is straight. I just checked it. Everything is fine. As a matter of fact, everything is almost brand new on it. I quit and left the bike in the garage. It time to ride it now.

The cable will not release or go loose when I release the smaller lever. Its not the front derailleur.

What kind of solvent? I know there are plastic parts in there.

Also, what's this flat plastic cable like thing in the lever? Some kind of electronic connection to a computer? My first gen. 9 spd didn't have anything like that in there. I thought it was it was something that got stuck in there causing the shifter to not work. I was dumb enough to pull on it and soon notice it was connected to something. Now I cann't shove i back in there. Can I cut it?

Alternatively, I've heard you can get Campy 11 speed shifters to work perfectly with shimano 9 speed everything else as is. Though I suppose if you're riding DA, you must like Shimano enough to stick with them and not go with the hybrid setup. I, on the other hand, am eagerly awaiting the arrival of my 10 spd centaur shifters to pair with my 8 speed cassette to try integrated brakes/shifters for the first time.