Last year I scored an older Troybilt Model number: 12AS5690063. The sellers got rid of it because the self propel isn't working. This thing runs like a champ, started on the first pull after winterization.
Since I like tinkering and learning about these old mowers, was going to attempt to fix the self propel. It does propel, but very slow. Front wheels engage when lifted. Will propel on concrete but not so much on grass. I figured it might be a worn belt. Removed the cover to reveal huge amounts of dirt. The belt looks pretty good to me but I'm not sure how tight its supposed to be. The drive bar does engage the cable at the transmission, although I'm not sure how far is fully engaged. I will continue to mess with it, perhaps look at tightening the cable.
Pull the wheels off and check out the drive.
I know othing about Troy Duilt SP's but there is always some shear pin arrangement as a fail safe device.
On some of the local mowers these are pins that break and even when broken can cause the wheels to rotate when there is not much load. leading
Did you ever get your problem fixed? I can't comment on your mower directly, but I have a Troy-Bilt, too, but a different model. Is yours a "variable" speed drive? Mine is. Your problem may just be the cable is worn and needs replaced.
The way the variable speed works is that there is a plastic gear inside the transmission on the output shaft (where the wheels attach to). There is a "fork" that moves this gear over onto the input shaft, which is spinning inside the transmission. The teeth of the plastic gear are tapered. As the speed lever on the handle is squeezed farther, the fork moves the plastic gear over more onto the spinning input shaft, which increases the speed. If the cable is stretched, the fork can't move the gear as far onto the input shaft, so you only engage the outer part of the teeth on the plastic gear, which is a slower speed than when it is fully engaged.
The other thing it could be is the "plastic" shroud that the transmission assembly attaches to/within underneath the mower. The outer housing of the cable attaches to this shroud(it fits into a plastic "ferrel" which protrudes and is molded right onto the plastic shroud), while the inner part of the cable attaches to the clutch lever sticking out of the transmission (which moves the fork inside the transmission). If that plastic shroud weakens or tears there isn't enough counter resistance offered so that just the inside of the cable moves and pulls the clutch lever fully. I hope that makes sense. If this is the case, you need to "beef up" the shroud somehow. You really need to watch it while squeezing the variable speed lever on the handle to see how this works. It really is a "rinky-dink" set-up if you ask me.
I forgot to mention that there is some adjustment for the cable up at the variable speed lever on the handle. I assume you already rotated the thumb screw and tightened up the cable? I would think if that doesn't do it, then the shroud underneath is "giving" too much and the resulting in the clutch lever not moving enough to engage the plastic gear onto the input shaft more to produce a faster speed. The arm of the plastic clutch lever has also been known to crack so that it won't rotate the fork inside the transmission.
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