I have a Sears reciprocating saw that failed because the drive shaft wore excessivley because the guide was not a traditional bushing, it is an iron casting, AND the manual provided absolutely no information about having to open the case and oil it (there is no oil port, so I didn't even think about it, so I'm partly to blame). And you can't get any replacement parts for any tool more than a couple of years old, I've had to make my own parts.
So, one had better take a good look at a machine before buying as the manufacturer may have been more concerned with their initial profit than the customer's long term satisfaction. And, there may be the calculation done, like Ford did, that dissatisfaction, or death, is a cost that they are willing to bear if failure is below a certain level.
The drive system needs some kind of a slip clutch. The teeth become disengaged well before the drive belt is sufficiently loose to disconnect the engine power. This is how the wheel teeth get chewed up.
That's pretty graphic, Armorris. I agree, the partial engagement is a very natural way of managing the speed of the mower. As a kid a mowed a ton of lawns, and you can't manage a lawn cut with a fully engaged drive (except on long straight stretches). With a fully engaged drive, you can dig ruts into the lawn when you hold back the mower on turns. So you have to slow it down with partial engagement.
As a matter of fact, I had been partially engaging the drive in order to slow down the forward motion of the mower, but that is normal use in my opinion. The engine has a governor and no throttle.
About 45 years ago, in high school, I worked part time for Sears as a TV repairman. Back then, they repaired only Sears products, and at reasonal cost.
My boss told me that Sears made their money on sales and that the service department was the "butt-hole" of the sales department. But if you let the butt-hole get stopped up, you'll see how much it's worth.
@Jaybird2005 I'm always extending the benefit of the doubt to manufacturers, having had to make some tough choices and comprimizes of my own when it comes to development. I didn't own the specific lawn mower in this story, but I would have hoped that if the design was for safety that advertising would have touted it as a positive, advertised this safety "feature", and then provided a spare polymer gear or two with purchase and stocked them in the department store at just over cost...
It does look like 'planned obsolescence', but it might also have been a safety device. If the mower gets up against something solid, like a tree, and the operator (possibly inexperienced) does not release the handle a metal-to-metal gear system may cause damage to the metal gears or cause the mower to bend it's deck or jump in an unexpected way. The existing system would simply strip the plastic gears. It may be better to have the mower stop moving than to risk some other, more severe, damage.
There may have been problems with stones or tree bark getting between the gears and causing severe damage (if they were metal) where the plastic might flex and allow the stones to be ejected with some minor damage to the plastic part rather than a gear grinding halt to the entire system.
On this particular instance, I wonder if the company didn't anticipate that users would use the mower's driver control to create a slower speed than fully engaged. Sounds like the user was adjusting the engagement lever to slow down the mower, which would mean the gears would grind insted of engaging.
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