Getting the Drive Belt Right on a Troy-Bilt Pony
The transmission belt on a Troy-Bilt Pony is one of those things that sounds straightforward until you are kneeling in the grass trying to route it and the manual diagram is doing absolutely nothing for you. I have replaced enough of these belts to know the common failure points by heart. The original Pony models from the 1990s and early 2000s with the Simplicity hydrostatic transmission use a specific belt routing that trips people up every single time because the tensioner assembly has a spring that fights you if you do not hold it correctly. Here is how the belt actually runs on the common 13 to 18 HP Pony models. The belt starts at the engine crankshaft pulley, goes down and around the tensioner idler pulley, then routes up to the transmission input pulley on the left side of the transmission case. From there it returns back down toward the engine area, passing around the spring-loaded tensioner arm one more time before re-establishing contact with the crank pulley. The deck drive belt is a separate belt entirely and does not factor into the transmission routing, though both belts get confused when people are working under the tractor. When you are ordering a replacement, the OEM belt number for most Pony models is 742-0448A, also known as a 6PK915 or MGA-915, which is a six rib serpentine belt approximately 91.5 inches in length. Some later Pony models with the 22 HP engine use a different routing and belt length, so verify your model number before you buy anything. The serial number plate is under the seat cushion on the frame rail.
I learned the hard way that the tensioner arm spring on these transmissions is under serious preload. I removed the old belt one afternoon and forgot to mark where the belt sat on the tensioner pulley before slipping it off. When I tried to reinstall it, the tensioner would not hold position long enough for me to guide the belt into place. What actually works is using a quarter inch breaker bar or a large socket on the tensioner arm pivot bolt to compress the spring and hold the tensioner in the fully released position while you slide the belt on. Keep the bar in place, route the belt, then slowly ease the tensioner back. It takes about five minutes once you have the tool ready, versus twenty-five minutes of wrestling with it bare handed. One thing nobody mentions in the diagrams is that the belt can install backwards on the tensioner pulley if you are not paying attention. The flat side of the belt faces the pulley grooves, not the ribbed side. If you route it with the ribs touching the idler pulley surface, the belt will pop off within ten minutes of running the tractor. I caught this on my second replacement attempt when the belt started making a loud chirping sound and tracking toward the edge of the pulley. Another detail that matters is the condition of the tensioner pulley itself. The bearing in these idler pulleys fails fairly often on Pony models after eight to twelve years. If you spin the pulley by hand and it feels grilty, rough, or makes noise, replace the pulley at the same time you replace the belt. Running a new belt over a bad idler pulley will destroy the new belt quickly and cause premature wear on the belt ribs. The pulley part number is typically 742-0415 or similar depending on your exact model year.
If you need an actual diagram to reference while you work, Simplicity publishes routing diagrams for their hydrostatic transmissions used in these tractors. You can find them on the Simplicity manufacturer website by searching your model number, or you can pull a copy from sites like partstown.com or searspartsdirect.com where they host OEM diagrams for Troy-Bilt equipment. Search for your specific model number plus belt diagram to find the PDF version. The common mistake people make is assuming the belt diagram for one Pony model year applies to all of them. The routing changed slightly between the 1998 and 2002 model years when Troy-Bilt moved from the Simplicity 428 transmission to the 448 transmission. The belt length is the same but the pulley positions shift enough that a diagram from the wrong year will leave you guessing at the routing. Always cross-reference your exact model and serial number before following any diagram you find online. There is no real workaround for a worn or glazed belt other than replacement. If the belt ribs are polished smooth from heat or the sides are frayed, it will slip on the pulleys even when properly tensioned. Slipping causes the tractor to lose drive power gradually, especially under load on hills. That is usually the first symptom people notice before they realize the belt needs changing. Inspect the belt ribs for glazing and check the tensioner spring for sag or deformation while you are under there. A weak tensioner spring will let a new belt go loose within a season.
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