If you find your riding lawn mower drive belt slipping, there’s a few common causes. This is usually a simple repair once we diagnose what’s causing the issue.
You’ll know if your drive belt is slipping because it’s simple to diagnose while in use. While applying the transmission pedal (forward or reverse), the machine will lurch. The transmission will catch and sometimes move the machine, but it won’t be consistent.
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There might be an audible noise from the belt slipping, and it might even smell like burnt rubber from the friction.
Regardless of the symptoms, the outcome is the same. If the machine does move, it won’t be efficient at all. Let’s look at some of the most common causes of a riding lawn mower drive belt slipping.
Condition of the Drive Belt
The first thing that we want to take a look at is the condition of the drive belt itself. Like any other consumable part on the machine, a drive belt will deteriorate over time.
Under normal conditions, a drive belt can last quite a few years, but they do need replacing eventually.
As the belt ages, it can gradually stretch from being constantly tensioned. This stretching of the belt means that there’s not enough tension left. Since the belt is no longer tight enough, instead of turning the drive system it will simply slip as that is less resistance.
Even if the machine hasn’t aged to the point of stretching, the condition of it can also warrant replacement.
If the drive belt is frayed, cracked, or nicked, that can also cause it to slip. Likewise, inspect the belt for any signs of oil leaks.
Perhaps you just changed the oil on the machine and spilled a bit. If that oil ends up on the belt, you can be sure that it will allow the belt to slip on the transmission.
Condition of the Pulleys
This includes any of the pulleys that are in the drive system of your machine. Most commonly involved is the tensioner pulley.
This pulley is the one that applies tension to the drive belt. If it’s not functioning properly, there won’t be adequate tension on the belt and it will slip.
It seems as though the manufacturing of this vital component is a bit of an afterthought. It’s a simple component, but it does a very important job.
Most of the tensioner pulleys have a bushing with a bolt through it to hold the pulley in place. Like any bushing, this is prone to wear over time.
Unfortunately, a lot of the brass bushings that used to be found are now being replaced with plastic bushings. As you can expect, this wears faster.
To check the tensioner pulley, remove the drive belt and see if there is any play in the bushing and pulley. Furthermore, inspect that the pulley is in line with the belt. If it’s bent, or out of alignment, that can also cause a belt to slip.
Build Up Debris
Finally, this is probably the most common cause. Thankfully, it’s a no-cost issue. Simply clean the machine.
As you use the machine, over time grass clippings and debris will build up. As we’ve mentioned in other articles, this can cause several issues.
Another problem it can cause is a drive belt slipping. That can either be because the debris is impeding on the path of the belt, or because it is engaging the brake.
On a lot of machines, the brake actually releases tension on the belt. This intentionally causes the belt to slip and no longer powers the machine. This type of brake system is in lieu of any sort of brake pad.
With debris built up, the pedal is not free to fully disengage. What happens is that the drive belt is held in limbo – partially engaged and partially disengaged.
If you inspect the drive belt and find that it’s loose but in otherwise good condition, check that there isn’t debris that is causing it to slip.
Recap
These are the three most common causes of a riding lawn mower drive belt slipping: debris, a worn belt itself, or a bad tensioner bushing. If you have more suggestions for things to check, let me know in the comments below.
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