Well, the self-propel feature of my 5-year old Honda mower recently stopped working. I sought the help of an expert online, and after first suggesting the belt (which was only $7, but made no change when replaced), he agreed that the transmission was the cause. So, off the Honda parts store I went, and $115 later, I had myself a new tranny for my Harmony II. When I was done, it sprang to life like new when drive was engaged, so color me happy.
Having found precious little assistance online about how to replace this thing, I muddled through it for about 3 hours, and so I figured I'd try to save the next guy who googles it a bit of trouble.
Tools you will need:
10 mm socket
10 mm open-end, ratcheting, or box-end wrench
12 mm socket
12 mm open-end, ratcheting, or box-end wrench
15 mm socket (1/2" preferred)
3/8" extender bar, at 8-12" preferred
hex (torx) adapter or tool for screwdriver
Leather glove, or something else to hold the blade still
fine tipped flathead screwdriver
phillips head screwdriver
brake spring tool (auto parts store for less than $10)
snap ring tool (auto parts store for less than $15)
hi-temp all purpose grease
brake parts cleaner
something (2x4)to prop up the back of the mower once the wheels are off
1. Get the mower at a comfortable working height (I used the tailgate of my truck), and lock the front caster wheels; turn the gas-line valve to OFF to help prevent leaking; lean the mower (gas tank side UP) so the underneath can be easily accessed.
2. Using the 15mm, 1/2" drive socket, remove the blade. Use something (leather glove) to hold the blade still while you loosen the 2 bolts that hold the blade on.
3. Using the 10mm socket, remove the 2 panels that comprise the belt cover. There should be 5 bolts to remove (2 on the smaller panel, 3 on the larger). You may need to utilize the 10mm wrench for those socket-inaccessible bolts.
4. The belt and transmission should be completely accessible now, so it's time to remove the belt (since you have to remove it anyway, you might as well replace it; only $7). The big spring attached to the gold colered Shift Arm is all that stands in the way, but it's a very strong spring. Using the vice grips, grip the spring just after the coil (on the coil side of the Shift Arm) and pull; then use the fine-tipped flathead screwdriver to pry underneath the hook of the spring and remove it from the Shift Arm. Pulling with the vice grips should release enough tension on the spring to allow you to pry underneath the hook with the screwdriver.
5. Remove the belt by rolling the transmission downward to allow it be slipped off the pulleys.
6. Disconnect the drive cable from the transmission. It connects to the tranny on the top-left (gas tank side), and is held in place by a hex bolt that holds down small guide plate for the cable. Remove the hex bolt and slide the guide plate up and out of its slot, and then rotate the drive lever arm forwards and unloop the end of the drive cable from it. (Removal of the speed control cable will not be done yet; at least I didn't think it was possible to remove it with the tranny still mounted in the mower).
7. Using the 10mm socket (and 10mm wrench) remove the other 2 underside panels (3 for the one, 2 for the other, IIRC). The bolt located above the transmission will require a long extender bar.
8. Time to remove the wheels. Using the 2x4 or other propping aide, prop up the back of the mower so the wheels are not touching the ground. Using the 12mm socket, loosen the wheel bolt, then finish removing it by hand, being VERY careful not to let the small washers on the back side of the wheel fall off the bolt. If they do fall off, the order I put them back on is: wheel -> flat black washer-> curved washer facing like so ( -> bolt threads.
9. Now it's time for the tough part, removing the snap rings. The use of a snap ring tool (my dealer called them C-rings, but an auto parts store will look at you like you're high if you ask them for a C-ring tool) is practically essential, so for less than $15, you can save yourself a massive headache, since there are 4 to remove and reinstall.
10. The axle has the has the following items installed on it (outside the mower frame) black interior wheel cover > thin washer > fat spacer > snap ring > midsize spacer > half-circle wedge inside the axle > sprocket > midsize spacer > snap ring. I used the 90-degree attachment on the snap-ring tool, and when you open the ring, it should open enough to allow you to lift it straight up off the end of the axle. Slide the sprocket and its first spacer off (they may be pressed together), and be very careful to catch the half-circle shaped wedge that is installed inside the axle under the sprocket, then slide off the next spacer. Remove the next snap ring in the same manner as before, and slide off the last spacer, washer, and black inner wheel cover. Repeat for the other end of the axle.
11. I cleaned up the sprocket and washers with brake parts cleaner, setting them in the correct reinstallation order for drying (if you install the sprocket in the wrong direction, the wheel will not roll foward). They were nasty, and I figured it couldn't hurt to have them clean.
12. Time to get the tranny out, so prop the mower on it's side (gas tank up), but be sure the right end of the axle has plenty of clearance because you're going to be sliding it that way. While rotating the tranny downwards, slide it towards the long side of the axle. The short side of the axle should slide out and be free from the mower frame, so now slide the tranny the other direction, making sure the short side is under the frame. The long side should slide out as well, freeing the unit from the frame.
13. Time to remove the speed control cable. Using a phillips screwdriver, remove the small screw holding the cable to the top of the tranny. Now rotate the pulley so one of the large holes is above the 2nd screw, which holds down a rectangle-shaped guide that's part of the cable. Remove the screw, then rotate the tranny and cable so that the cable's "S"-shaped end can be removed from its retaining hole. That's it, the tranny is out...BUT you're not quite done with it.
14. At each end of the axle, there is a groove cut into it that houses the half-circle wedge, as well as a very small spring. I was surprised to see that my new tranny did NOT include new springs, so make sure you remove the old springs and install them in the new axle.
15. On the old axle, there should be 2 black plastic sleeves on each end; well, one sleeve and one cap. Remove them, making sure to keep them oriented correctly (the flared end of the sleeve is closer to the transmission, and the cap is inside that, with the flat top on the inside).
16. Installation is just the reverse of the above. I used some hi-temp all purpose grease as I installed parts back onto the axle. As far as the snap rings go, to reinstall them I opened them with the tool and slid them straight down the axle until they hit their groove (if you open and lift them off the end of the axle, they should not become deformed and can be reused, otherwise buy new ones for 50 cents each). The half-circle shaped wedge is installed with the curve facing the spring, so the flat part engages with the inside gears of the sprocket. Make sure the sprocket is facing the correct direction, otherwise the wheel will not roll foward (how do I know?) after assembly. The side of the sprocket that contacts the wheel gear should look more silvery, and goes toward the outside.
17. For reinstalling the spring to the Shift Arm, I bought a brake spring tool, and I used the flat end of the Shift Arm as the tension point for the tool. It took a few times because it kept sliding off, but just stick with it and you will figure out a method that works for you.
Hopefully this works for you and will save you a little time. If so, leave a comment. Also, if some of my instructions are misleading or vague (or just plain wrong), leave a comment so I can fix them.