# Understanding a Variable Speed Transmission



## How Do I (Feb 11, 2008)

This newest riding mower I got, the Troy-Bilt, has a variable speed transmission. I'm trying to wrap my mind around how it works.

There are two belts. One from the engine to the transmission (lower). The other (upper) is for the speed management, once engaged by the pedal. I changed the spring, the idler pulley (had locked up) and the upper belt (<--see idler pulley ). So I should be good to go, right?

Well, it still only wants to go verrrry slow. You can push the pedal to the floor and it still doesn't want to go fast. I talked to a guy at the shop and he said the pulley itself should rise and fall depending on how much pressure there is on the upper belt-spring-pedal.

He said you could pull the battery out and pull on the pulley itself to see if it isn't stuck. I tried that, but it only moves maybe a half-inch until it hits a bolt, maybe a retaining bolt? How much should it actually move?

If I push the pedal all the way down manually, and set the 'cruise' it will go 'faster', but doesn't seem to want to and after you're on cruise awhile, you eventually lose speed until like you would be in first gear again. So it is like it backs off. Even when you try to set the cruise, it tries to set itself at a lower speed than where you tried to set it. If that makes since.

Any ideas on what I should be checking out now?


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## davel745 (Feb 2, 2009)

Some transmissions work on a cone that slides on a shaft and it changes the speed of the lawn mower, These are basically crap and don't last to long.

There used to be a replacement /conversion kit but they don&#8217;t have any more. You can buy a new transmission for around 600 or rebuild yourself, Not recommended. 
Any way you go the transmission wont last to long.


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## Travis in Louisiana (May 14, 2002)

I have the TROY-BUILT lawn mower with the varible speed. I have had it over seven years and have not had a bit of trouble. I did look at the belts and they do need to be changed. Here is an artile on how the system works.

Pulley
The variable speed pulley used on a Troy-Bilt riding lawn mower is composed of two pieces, the fixed frame and the sliding center groove plate. The sliding groove plate slides between the two fixed frame grooves. As the plate slides one way, the pulley formed by one side of the fixed frame and one side of the sliding plate will either get larger or smaller. As one side gets smaller, the other side gets larger.

Drive Belts
One drive belt goes from the engine to one side of the variable pulley. Another belt goes from the transmission to the other side of the variable pulley. The tension on these belts is equal when the mower is in operation.

Changing Ratio
The variable speed pulley is mounted on a sliding plate, which moves the pulley toward the engine or toward the transmission. As the pulley moves toward the engine, the transmission belt gets tighter. This forces the sliding plate in the variable pulley to squeeze the engine belt. The harder the engine belt is squeezed, the higher the engine belt will ride on the engine belt side of the variable speed pulley. Since the transmission is being driven by the variable pulley in its lowest setting, the transmission has more power and less speed.

If the variable speed pulley is moved toward the transmission, the engine belt will force the variable plate to squeeze the transmission belt. The engine belt will then move to a lower setting on the variable speed pulley while the transmission side will begin to ride higher. This causes the transmission to turn faster with less power.


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## How Do I (Feb 11, 2008)

Travis in Louisiana said:


> I have the TROY-BUILT lawn mower with the varible speed. I have had it over seven years and have not had a bit of trouble. I did look at the belts and they do need to be changed. Here is an artile on how the system works.
> 
> Pulley
> The variable speed pulley used on a Troy-Bilt riding lawn mower is composed of two pieces, the fixed frame and the sliding center groove plate. The sliding groove plate slides between the two fixed frame grooves. As the plate slides one way, the pulley formed by one side of the fixed frame and one side of the sliding plate will either get larger or smaller. As one side gets smaller, the other side gets larger.
> ...


Thanks Travis! I'll have to print this off and take it out to the mower to visualize it better.


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## agmantoo (May 23, 2003)

Excessive wear, dirt and lack of lubrication can cause the half of the pulley that moves to wedge rather that slide in and out. The movement needs to be smooth for the tranny to work.


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