The black plastic part on the side of my Dyson D25 has come unattached. One end of it has a spring that is still attached to the vacuum, but the black plastic end is unattached. Is there a diagram so that I can reattach it?

As long as the black piece still has the "nubs" on both sides at the turn in the "L" shape and the base isn't broke then this is going to be easy. There is a groove on the main unit the little wheel fits into that groove, the "nubs" fit into small holes on the swivel down piece, and the spring fits between the small side of the "L" shape and the bottom of the swivel down piece..

call dyson and explain to them they will help you

Hi Natalie,

If the hose lock button seems to have broken, the hose will need to be replaced. You can order directly from us by visiting our online store:

http://www.dyson.com/store/spares.asp

Alternatively, if you'd prefer to order over the phone, or would like to speak to someone before making a purchase, you can call us free on 1866MYDYSON.

Kind regards,

Jack
Dyson Online Customer Support

Hi Pete,

Unfortunately we can't supply directions on how to fit this part, as this sort of repair should only be carried out by a Dyson engineer.

If you're unable to get assistance elsewhere, I'd encourage you to get in touch with our Helpline by calling free on 08002980298 (UK), or 1866MYDYSON. One of our experts will be happy to recommend the best course of action.

Kind regards,

Jack
Dyson Online Customer Support

That spring thing goes where the pedal screws into the side. When 'facing' the dyson in the front, it's on the left side. The spring's circle part and short stem section goes into a divot area on the pedal. The other end is tensioned (braced) against some housing piece, but once you insert the spring part in the pedal end part, you should be able to figure it out from there.
This darned spring makes the pedal 'tensioned' to where it pops back up vs. flopping nonsensically.

I have just cleaned mine just a half an hour ago - SAME PROBLEM !!
ok take the dust cylinder off the vacuum cleaner and take the plastic clear cylinder off - there is a clear clip one side and you might need a small knife to unclip other side. PULL the clear away from motor with the fins and suggest you get a coat hanger, turn the end slightly and gently rod the dust out from the central core - LOADS will come out.... clean it totally !!. Then re-assemble.

Point to note... the cover at the bottom where the brush roller is needs to be carefully clippd FULLY and re-tighened (white plastis screw heads) - The suction should be back !! you'll find that after cleaning all the filters and fully drying them - the machine will be working almost as new.... JUST DONE IT MYSELF. Good luck

You'll see that there is a round piece with a cross shape on the inside of the button wand release button - place the end of the spring over the cross - you'll see the same cross on the collar of the machine...it'll take some doing, but line the other end of the spring up with the cross and pop the button back into place - be sure to click it onto those two gray circular/oval shaped divets at the bottom where the release button connects to so that the button stays in place.

As long as the black piece still has the "nubs" on both sides at the turn in the "L" shape and the base isn't broke then this is going to be easy. There is a groove on the main unit the little wheel fits into that groove, the "nubs" fit into small holes on the swivel down piece, and the spring fits between the small side of the "L" shape and the bottom of the swivel down piece.

There is a clog either in the hose or the wand/hand

Not necessarily. Some Dyson models have an all inclusive flexi hose which attaches to the handle spine. Check EBay for replacement flexi hoses - UK has many sellers - or handles which have the metal pole and the flexi tube attached. 
Alternatively take off the flexi hose from the bottom rear of the Dyson - it can come out via a press in lock release but it may take some time to do this. Once that is done the flexi hose should come down freely from the metal tube. If it doesnt then you may need to consider both replacements.
Dont forget to rate, thanks.