Troubleshooting Slow Troy Bilt Bronco (2011) - FIXED!

dan2fs2ns

Forum Newbie
Joined
Jun 30, 2020
Threads
1
Messages
6
Model: 13WX78KS, 2/2011

Only getting about 2.5mph out of the mower forwards/reverse. I've been lurking as this is a common problem but I think I've hit all the major points. New MTD upper/lower belts, and the routing is correct. The variable speed pulley seems to be working, but I'm starting to think maybe not all the way? When I apply pressure to the main drive belt the upper belt that drives the transmission does get wider, but I don't think it gets wide enough, maybe that center part isn't moving completely up/down? I found one youtube of a guy showing how his worked, and the belt almost seemed to ride around flush with the outside of the pulley, mine however only gets to about halfway.

I have also replaced the tension spring for the upper belt pulley with a new one.

My upper belt at rest, no gas:
my pulley disengaged.jpg

My upper belt full throttle, pedal to floor:
my pulley engaged.jpg

Video of my pulley in action:

Video I'm comparing my pulley to:
 
Last edited:

dan2fs2ns

Forum Newbie
Joined
Jun 30, 2020
Threads
1
Messages
6
Here's a video of the variable speed pulley movement, seems clean/complete.

 

keakar

Well-Known Member
Joined
Apr 28, 2020
Threads
14
Messages
259
most common issue is the belt needs replacing, the belt sides are the only thing that wears so the belt can still look great but be worn out.

second most common issue is the small tranny tension spring to the frame rail gets rusty and weak, they only cost $10 to replace and to replace it, hook it to the pulley arm and run a heavy cord through the other end then use the cord to pull the spring through the hole to hook to the frame
 

dan2fs2ns

Forum Newbie
Joined
Jun 30, 2020
Threads
1
Messages
6
most common issue is the belt needs replacing, the belt sides are the only thing that wears so the belt can still look great but be worn out.

second most common issue is the small tranny tension spring to the frame rail gets rusty and weak, they only cost $10 to replace and to replace it, hook it to the pulley arm and run a heavy cord through the other end then use the cord to pull the spring through the hole to hook to the frame

Thanks for the info! As mentioned in original post, I did replace belts with OEM and the tranny tension spring. I've since even sanded down pulley faces to reduce any glazing.
 

dan2fs2ns

Forum Newbie
Joined
Jun 30, 2020
Threads
1
Messages
6
Here's a video my brother took of his pulley, the upper belt is for sure getting moved out on that variable speed pulley much farther.

 

dan2fs2ns

Forum Newbie
Joined
Jun 30, 2020
Threads
1
Messages
6
You can also see on the top belt that goes to rear axle, the wear marks are not moving full out to the edge of the pulley.

pully wear.jpg

Versus on my brothers, it's shiny to the edge:
pulley good wear.jpg
 

slomo

Well-Known Member
Joined
Jul 14, 2019
Threads
25
Messages
914
Sounds like you need a new variable pulley then.

slomo
 

dan2fs2ns

Forum Newbie
Joined
Jun 30, 2020
Threads
1
Messages
6
Problem identified and solved!

The arm on the gas pedal bracket has apparently bent over time, so its throw was shortened and was not creating enough tension on the transmission belt.

In the image, new assembly is on the left, old on the right. The highlighted green line is where the arm should be...
bent arm.jpg
 

slomo

Well-Known Member
Joined
Jul 14, 2019
Threads
25
Messages
914
Nice find there dan2. Wonder how that arm got bent? Might need to keep an eye on it in the future? Probably some heavy footed drivers LOL.

slomo
 
Top