Take the cover off and look at the drive gear. It is white nylon and is just in front of the motor. Most likely stripped. It is available at Sears or any good opener service company and comes with instructions. The part number if 41A2817.

Congratulations. You own the worst garage door opener ever made.
Cut your losses and chunk the Craftsman garage door opener. Get a Genie and you will never post a question about openers on this forum again. A little research on this forum will show you hundreds of posts about those badly engineered and cheaply produced monsters. There are probably more questions about them than anything else on this forum. I recommend the Genie "Excelerator". Opens twice as fast, quiet, has two lights, and extremely reliable.

Two Crapsman OH door openers were on my garage when I bought the house. When one crapped-out in '97, I called the Sears tech who replaced a circuit board for 100.00 - yikes! What was I thinking?

I still have that repaired one - just waiting for it to have a second death so I can replace it with the Genie I bought to replace the second unit which stopped working a year later.

I swear it's a Sears conspiracy for planned obsolescence. :^)

Don, That was exactly it. I got the parts pretty cheaply had not trouble at all installing them and everything seemed to be fine. Now I'm having trouble with the door getting almost all the way closed and then going back up. I adjusted the limits and those are fine because occasionally it closes. Most times not. I also adjusted the down force as much as it would go. and the sensors are fine. It looks to be binding right at the end. anyone run into this or have a suggestion?

You thought I was kidding didn't you? Just go on and keep buying stuff for that Craftsman Garage Door Opener. Before you know it the parts cost will exceed the cost of a new one not to mention the headaches. Just when you really need it to work it will fail....on a weekend.

rdaystrom why don't you go find a sandbox to play in.

jerjones here are some tips to try.

Make sure you put the black cup back on the end of the motor shaft and that it is pressed all the way on. Make sure the RPM sensor is plugged in. If neither of these are the issue, then you probably did not have the motor shaft pushed all the way back when you tightened the coupler after replacing the worm gear. Loosen that coupler up and from the front of the motor (opposite end in which the coupler is on) push the shaft back as far as it will go. Hold it there while you tighten the coupler back up and then try it.

don_1_2006, Save your childish remarks for someone else. It's too bad you can't recognize one of the worst engineered machines on the market. The Sears Craftsman line of garage door openers. The most failure prone pieces of junk ever built. Perhaps you do not have the experience or have not seen as many Craftsman Garage door opener failures as I have. To those readers out there who wish to eliminate this headache from their lives, just replace the thing before you spend more money and time on a machine that was built with failure in mind. This type of design creates a huge replacement parts market for Sears. They can make massive profits on replacement parts with a captive market. Buy a Genie opener and you will not be posting questions here anymore about Garage door openers.