DeWalt DW 421 palm sander. Sander was working. All at once it lost power.Did not quit, just slowed down. When I lifted it off the board it sped up,but when I tried to sand again it slowed down-lost power. Motor runs fine when it is not in contact with a board. Just no sanding power. I did check the brushes and they appeared to be in contact with armature.

the vanes in the small air motor are stuck
try a small amount ( couple of drops ) of sewing machine oil in the air inlet and see it it will spin
you may need to bump the pad on the bench to jar the shaft to start rotating

The answer "Go to Dewaltservicenet" can be confusing - the actual site is servicenet.dewalt.com and even then, entering your part to get to manual can be infuriating. This is the link for the current model which, for all intents and purposes, is the same. The link to the helpful page is: http://www.dewalt.com/tools/woodworking-sanders-orbital-sanders-d26441k.aspx . You'll get a pop-up box with a dropdown that has a few numbers, nothing else. Just click on "1" and ignore language that indicates that this model has more than one - it does not. After you click on "1", the pop-up disappears that you're on the d/l page. Downloads are in the upper right corner. You want "Instruction Manual".You should get to this page: http://servicenet.dewalt.com/Parts/Browse#6229 but may not, it's very glitchy. On this page, you'll want to make sure "Sanders" is on the left and "sheet" is on the right. If you try to get the Manual from the DW411 page, a blank page will open. Make sure your pop-up blocker is off or that you allow dewalt.com. The instructions for the d26441k are identical to the dw411 - same technique for loading sanding sheets, same rods, etc. I've uploaded the d26441k page manual .pdf so that should help. It's easy to get lost on the Dewalt site while trying to find somthing so simple. :)

There are no parts in your sander to grease. The only place there is grease is in the three sealed bearings on the armature and in the platen. Everything should be clean and dry inside the sander to make it less likely for sawdust to stick inside the tool. Blow everything out and replace the bearings if they are not turning freely and smoothly.

You may try a two part epoxy, or gorilla glue. Let dry for a day or two. Sometimes 3m spray adhesive also works. Let tack before sticking together though.

That sounds right. It is probably the type that uses adhesive backed paper. You stick the paper to the rubber pad.

I think your model holds the paper with glue that is on the sand paper.Just take apart the back cover of the sand paper to expose the glue.

go to Dewaltservicenet.com and in the midle of the page and towards the bottom under need manual type in your model number and you should be able to download anbreakdown and operators manual

I have the same problem with a Porter Cable orbital sander I recently purchased. Whats happening is the sander is catching the edge of the board you're trying to sand and jerking back and forth as the sander base spins. It seems that if the board your're sanding is at least as wide as the sander base, the problem goes away, which does little good because there will be many times I we'll need to sand wood that is less in size. But you may try using a lesser grit sandpaper and see if that alleviates the problem somewhat.

The velcro pads wear out and need to be replaced periodically. You can buy new pads on-line at any Dewalt parts seller.

grab a corner of the paper and peel it off