Many people still buy and use a NordicTrack Ski Machine, although these machines are not as popular as they once were. I have talked to people who say they just plain wore out a ski machine. The part that wears is the one-way clutch inside the drive rollers. NordicTrack makes the one-way clutch sound very mysterious. In reality it is a one-way needle bearing and is available from Amazon or locally from a good bearing shop. The internal diameter of the one-way needle bearing used in my machine (Challenger, similar to a 303) is 5/8 inch. The outer diameter is 7/8 inch. The width of the one-way needle bearing from end to end is 5/8 inch. I originally had hopes of being able to install new one-way needle bearings, myself; but, they together with the bronze sleeve bearings on either side of the one-way needle bearing inside each drive roller are pressed into place. Pressing bearings is not a job for the average home tinkerer but requires a bearing press capable of exerting tons of pressure in a very precise manner. You can often have a local machine shop press the bearings in your machine's drive rollers. Or, you can send them away to Nordic Track Guy and have them rebuilt for about $33 with a one week turnaround. The core of the rollers really does not wear out, but new rollers are available on the Internet from $65 to $95, depending on the vendor. From what I can find, some models used an alternate size. Check to be certain you order the correct rollers, if you choose to replace. One of my drive rollers suddenly began to hiccup. It seemed that the clutch did not always release immediately when I pulled my foot forward. Then I noticed a little mush in the response when I began to bring my foot back on the push stroke. Before you rebuild or replace your rollers, try this: Remove one side of your Ski Machine. See the second photo and check the exploded diagram in your manual. Four nuts and two screws, all plainly visible, need to be removed. Slide the washers and the roller off of the top side. The shaft and flywheel can be wiggled out of the other side without removing anything from that side. Remove the washers and the roller from that side, too. Flush the one-way needle bearing by squirting some penetrating oil, like Liquid Wrench, into the bearing. Work it both ways with your smallest finger. Push a facial tissue into the shaft hole in the roller and sop away the penetrating oil and any metallic dust it lifts. Do this several times. Let the rollers air dry. A little lubrication is good. People who comment on lubrication for one-way needle bearings use Tri-Flo (I am not familiar with it.) or they use a little ATF transmission fluid. You want enough to lubricate, but not so much that the bearings slip. (But, see the comments below where the oil impregnated bronze sleeve bearings are supposed to supply enough lubrication for the needle bearings.) Put the rollers back in place on the shaft. Check to be certain they grab on the rearward stroke and release on the forward stroke. Reassemble the machine. Do not forget the washers between the roller and the side board. My machine works again as it should. The day will likely come when this simple fix does not help, and I will need to rebuild or replace the rollers then. But, for now, my rollers have a new lease on life. What follows is for your information. The first photo is of a portion of the back cover of the manual that came with my machine. It shows a cutaway image of the drive roller. The black printing is mine. Notice the three cylinders inside the drive roller. The outer two are bronze sleeve bearings. The center one looks like a roller bearing, but is a one-way needle bearing. A one-way needle bearing is essentially a roller bearing, but the rollers are able to move forward and backward a little in their cage. There is a wedge shape for the axle of each roller that causes the rollers to bind between the bearing cage and the shaft when the rotation is in one direction, but they are free in the other direction. Here is a description of how they work with graphics. This link is for an Instructable about a number of modifications I made to our NordicTrack ski machine, including how it can be stored vertically in a closet. If you do not have a digital monitor for your skier, or need to replace one, here is an Instructable on how to make your own from a digital bicycle speedometer. Check NordicParts for any parts you need, also Nordic Fitness Ski Machines. Danny at Nordic Fitness Ski Machines has some very nice new rollers for sale.