Drive system not working

There is an inspection pan on bottom of snow blower remove the 2 or 4 bolts and drop pan
inside you will see an aluminum wheel (drive wheel) also a rubber faced wheel whitch runs on the aluminum wheel at a right angle (like a needle runs on a record on a record player.
Clean plate and rubber wheel using brake clean to degrease surface .
Also there is an adjustment to move the rubber wheel farther to the left for more reverse speed but in doing that you might lose top speed forward.

Possibly the friction wheel or drive belt need to be replaced

Check drive belt. has it come off the pulleys or is it broken. They do those things once in a while. Check for broken shear pins in the pulleys as well

yes adjust the linkage so the drive wheel goes past center
of the alum drive disk

the drive wheel is worn out or tension on the wheel needs adjustment

Howdie ther is Clutch under the bottom of it that needs to be replaced take the cover off and you will see it

Can anyone help me with a john deer 826 snow blower that won't engage in forward motion?

Make sure keep your system up to date. Getting W7 SP1 should fix this issue

ALL SNOW BLOWERS HAVE WHAT THEY CALL A FRICTION DISC DRIVE IT SOUNDS LIKE THE FORWARD SIDE OF THE DISC IS WORN OR THEDRIVE WHEEL HAS A RUBBER DRIVE RING THAT IS WORN. IF YOU REMOVE THE BOTTOM PLATE YOU WILL SEE TWO DRIVE WHEELS ONE IS JUST A METAL DISC AND THE OTHER LOOKS THE SAME BUT HAS A REBBER RING FOR GRIPPING THE DISC TO MOVE THE BLOWER FOREWARD, WE END UP REPLACING ALL THE DRIVE DISC AND DRIVE WHEELS ON OURS EVERY SPRING THE FOREWARD DRIVE TAKES THE MOST PUNISHMENTTHERE FOR WHEARS OUT THE FASTEST. MTD HAS A WEB SITE FOR ORDERING PARTS AND ARE NOT HARD TO INSTALL.GOOD LUCK LET ME KNOW HOW IT GOES

Try lubing the linkage where it shifts from forward and to reverse the linkage is most likely freezing up or has snow or ice build up causing it not to shift, My thought is your shoving it hard enough that it finally engages when you get the snow or ice to break off.