I have a John Deere Riding Mower L100, a manual shift, no frills, bottom of the line model which is now obsolete (I believe). It is probably over 15 years old and in good condition. The engine runs well, but the cutting belt (i.e., the belt driving the mowing blades) keeps slipping off the pulleys. As I last recall, a friend was able to rig it so a belt that was 1-in smaller than recommended fit the mower. (Who knew they made off-sizes?) It worked for awhile, but then the belt kept slipping after maybe 10-15 minutes of use in thick grass (last mowing season). Note: The pulleys are nice and shiny, but I guess that doesn’t mean their shot…or maybe the tensioner and/or its spring is shot?
Sooo, while I do not know the root cause, does this sound like the pulleys may be “out of spec”? And, if so, is it worth the money to diagnose and fix vs. sinking the same money into a new mower? And, if you were to buy a new mower, what brand mower is the best buy? Yes, my John Deere had a quite a life with just basic maintenance (mostly). But, could there be a less expensive alternative? (Last, what do people do with old riding mowers? Do they have any trade-in value at some tractor stores?) Help before it’s growing and mowing season again! :eek:
It’s the not pulley getting smaller…
Something is out of alignment. One of the pulley mounts is loose, or bent, of something along those lines. You probably need to examine it from the bottom (NOT RUNNING!) to see what is wrong, but it should be visible - everything that the pulley drives should be exactly in the same plane, and nothing tilted or wobbly.
It is possible for pulleys to fail, but the tension spring’s a more likely candidate. Also, there are belt guards that help keep the belt from slipping off. These can get easily bent by sticks or other detritus and by the belt itself when it breaks. It’s definitely worth looking into if the only problem is the belt slipping off. It could be as simple as a miss-routed belt.
With a little Googling, you can find the owner’s manual online to find out how the belt needs to be routed and where and how any tensioning springs are attached. Sometimes they have adjustment holes.
Also make sure everything turns freely. A frozen or stiff pulley can cause belt slippage that will quickly burn up a belt. A bad tensioner or frozen pulley would be my first suspicion or pulley being loose and out of alignment. It should be easy to figure out if you look closely at all the components involved.
Here’s a photo of the 42-inch mower deck showing the belt routing. I have a newer model Deere and the bearings on one of the pulleys (the large silver one on the right in the photo) failed. It was easy to tell because the pulley wobbled around the shaft.
It was easy to replace; the hardest part was removing the deck from under the tractor. The deck really needs to be removed for cleaning and lubrication yearly (I believe the spindles under the big pulleys that drive the blades have grease fittings on them and need to be serviced). If you aren’t handy enough to remove the deck yourself and diagnose the problem, take it to a shop; if the engine and transmission run well, it is much cheaper than a new one. Even if the spindles have worn out because of lack of lubrication, a kit that includes those, a new belt, and new blades can be had for less than $100.
I had an old snapper mower once that everything was aligned, but one of the idler pulleys had a bad catchy spot on the bearing it rode. It was enough to sling the belt weird when I hit tall Johnson grass, but when the belt was off the bad bearing felt like no big deal. I didn’t believe that it could be the pulley but my dad swapped it out and it never shit the belt again.
Mine is a 1991 Honda 5013. I have, and still would, replace pulleys and bearings before even considering a replacement. It falls under my general theory of “never get rid of a good motor and transmission”.
