To work on the drive unit (or "transmission"), the snowblower needs to be tipped on its face.

Gasoline may leak out of the fuel tank when the snowblower is tipped over. Placing a sheet of plastic (in this case a plastic sandwich bag) under the gas cap will prevent fuel from leaking out of the small vent hole in the cap.

I've found that this step is not necessary if the gas tank is less than half full.

When I removed the cover, there were a lot of metal and rubber shavings inside. That's not a good sign.

Rubber shavings would be expected as the friction wheel wears, but metal particles indicate wear on metal portion of the friction wheel, and possibly the drive plate.

The drive plate (1) gets pulled against the friction wheel (2) to make the snowblower move forward or backward.

The gearshift simply slides the friction wheel sideways along a hexagonal shaft. In lower speeds, the friction wheel is closer to the center of the constantly-spinning drive plate.

In reverse "gears", the friction wheel is located to the right of the center of the drive plate, causing the friction wheel to turn the opposite direction.

Note how the rubber on the friction wheel (1) is worn down flush with the "pulley" it's fastened to. That's not good.

Also, the drive plate (2) has a lot of grooves cut into it, which explains the metal shavings I found earlier. I will need to replace this part.

Arrow 3 points to the metal bracket that holds the drive plate.

Another, separate problem: The hook on the spring on the end of the drive clutch cable broke a couple of weeks earlier. I bent the broken end into a hook (I had to heat the metal with a propane torch) but the hook kept bending and letting go.

(Read more about replacing the broken hook.)

This hook is connected to a hole (red arrow) in the pivoting bracket that contains the drive plate, and when the drive clutch handle is engaged (i.e. pushed down), the drive plate is pushed into the friction wheel, causing the axle to turn.

I removed four bolts (red arrows) on the left-hand drive cover, using a 3/8" deep-well socket.

I carefully pulled off the left-hand drive cover.

There is a hex-shaped washer and washer behind it that fell off when I removed the cover (red arrow).

I pulled the hex shaft out of the left side.

A chain sprocket and spacer fell out of the right-hand side when I removed the shaft. The bearing fell out too.

At this point the drive plate (red arrow) is accessible. A belt connects the drive plate to the output shaft of the engine.

If the friction wheel rubber never gets badly worn, the drive plate should never need replacing (unless the bearing goes bad). The drive plate on my snowblower had developed some deep grooves, so I ordered a replacement along with the friction wheel rubber.

Read about Replacing The Drive Plate.

There are 6 bolts holding the two halves of the friction wheel together, 3 on each side.

The bolts on the side with the bearing are kinda difficult to reach.

It seemed almost impossible to hold the friction wheel while turning the bolts, so I placed the hex shaft in a vise and placed the friction wheel on the shaft. Then I used a 3/8" offset-end wrench to remove the bolts on the bearing side. The bolts on the other side can be removed with a socket or regular wrench.

NOTE: I used two small blocks of wood to hold the hex shaft in the vise, to prevent the shaft from being marked or gouged. Since the friction wheel slides back and forth along this shaft, it needs to be keep smooth and free of nicks and burrs.

The new friction rubber (MTD part no. 935-0243B).

This part has an outside diameter of 4.875" (4-7/8 inches).

I installed the new friction rubber on the wheel. First I cleaned the inner surfaces of the metal halves with brake parts cleaner. I placed the rubber "donut" on the metal pulley and assembled the two halves, making sure the rubber was placed so it protruded uniformly.

I placed the the friction wheel on the hex shaft (still in the vise) and tightened the 6 bolts uniformly, turning each a little bit at a time until they were all tight.

Installing the friction wheel was a reversal of the procedure to remove it, with one exception. There is a hole on the bearing body that needs to slip over a "nub" on the shift linkage... while the hex shaft is inserted from the left side.

Then the small chain sprocket needs to be placed on the right-hand end of the shaft, along with the spacer bushing. The end of the shaft then goes into a bearing which is held in the side of the snowblower housing.