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Troy Bilt 12av834q711 simple gearbox repair.
#1
B
beng
B
beng
Hi all,
I was disappointed when searching for repair information on this type of self-propelled push-mower so once I figured out a simple fix for mine I thought I would pass it along. My mower would not move when the lever to activate the self-propel was engaged, but the wheels would spin if I lifted the rear of the mower off the ground. Most easily found advice on the internet tells people to replace the entire gearbox for $100 or to scrap the mower. Here is how to fix it for ten cents.
I took the gearbox/axle assembly completely out of the mower and split it's case by removing the eight little torx screws. I saw that the large plastic gear that slides to engage the metal worm gear had just the tips of it's ratchet-ramps worn because the factory set it up to only move enough to catch the tips of those ratchet ramps. This wore the tips of the ramps enough so that it did not engage well.
The easy solution is to simply put a few more washers in between the two that are already there against the back of the plastic gear which the engaging lever works against. This lets the lever force the gear fully over so that the drive pin engages the ratchet-ramps very fully and restores full function to the gearbox. It also puts the drive pin back far enough on the ramps so it is very unlikely to fail again, it was surely a factory error or shortcut to have the drive pin engage the very end and weakest part of the ramps.
Axle assembly as removed. You will have to drive out the small pin because with the new spacers you are going to add you will not be able to remove the longer pin as the gear will be around it.:
Parts removed from shaft, still have to get that little short pin out, you need the right sized drift to do this, and it can be tapped back into place with a small hammer:
Back together with two regular flat washers placed between the two existing smooth machine washers. Note also that you have to remove the engaging lever mechanism from the gearbox case to get the axle/gear assembly out. This involves removing the drive pulley and the metal plate below it that covers the top of the plastic engaging lever. This all has to be done cleanly and patiently of course.:
Mower back together and working well. I used some GM 80/90 differential lube to refill the gearbox, it was handy and smelled and felt the same as the lube that was originally in it.
I noticed that sometimes once the drive lever is pulled back, I have to pull the whole mower back an inch or two to get the drive to engage, then it takes off like a jack-rabbit. Sure wish this mower had a manual throttle, maybe that will be my next project.....
I was disappointed when searching for repair information on this type of self-propelled push-mower so once I figured out a simple fix for mine I thought I would pass it along. My mower would not move when the lever to activate the self-propel was engaged, but the wheels would spin if I lifted the rear of the mower off the ground. Most easily found advice on the internet tells people to replace the entire gearbox for $100 or to scrap the mower. Here is how to fix it for ten cents.
I took the gearbox/axle assembly completely out of the mower and split it's case by removing the eight little torx screws. I saw that the large plastic gear that slides to engage the metal worm gear had just the tips of it's ratchet-ramps worn because the factory set it up to only move enough to catch the tips of those ratchet ramps. This wore the tips of the ramps enough so that it did not engage well.
The easy solution is to simply put a few more washers in between the two that are already there against the back of the plastic gear which the engaging lever works against. This lets the lever force the gear fully over so that the drive pin engages the ratchet-ramps very fully and restores full function to the gearbox. It also puts the drive pin back far enough on the ramps so it is very unlikely to fail again, it was surely a factory error or shortcut to have the drive pin engage the very end and weakest part of the ramps.
Axle assembly as removed. You will have to drive out the small pin because with the new spacers you are going to add you will not be able to remove the longer pin as the gear will be around it.:
Parts removed from shaft, still have to get that little short pin out, you need the right sized drift to do this, and it can be tapped back into place with a small hammer:
Back together with two regular flat washers placed between the two existing smooth machine washers. Note also that you have to remove the engaging lever mechanism from the gearbox case to get the axle/gear assembly out. This involves removing the drive pulley and the metal plate below it that covers the top of the plastic engaging lever. This all has to be done cleanly and patiently of course.:
Mower back together and working well. I used some GM 80/90 differential lube to refill the gearbox, it was handy and smelled and felt the same as the lube that was originally in it.
I noticed that sometimes once the drive lever is pulled back, I have to pull the whole mower back an inch or two to get the drive to engage, then it takes off like a jack-rabbit. Sure wish this mower had a manual throttle, maybe that will be my next project.....