Troy Bilt bronco 17.5 hp mower is slow

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I just bought a used Troy Bilt bronco riding mower. Even without the blades running, it will only run at about a maximum of 2 mph on flat ground.
I’m wondering if anyone can give me some advice as to why it doesn’t move faster?
 

bertsmobile1

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With vari speed mowers slow running is usually due to a stuck variable pulley or worn out belt.
Try pulling the brake pedal up.
If that makes it go faster then the clutch needs attention.
Do you have the owners manual for this mower ?
Some of them have fixed speed ratios which limit the travel of the GO pedal
Because these transmission work on balancing spring pressures, a misplaced tension spring on either the upper or lower belt will also cause it to run slow.
 
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With vari speed mowers slow running is usually due to a stuck variable pulley or worn out belt.
Try pulling the brake pedal up.
If that makes it go faster then the clutch needs attention.
Do you have the owners manual for this mower ?
Some of them have fixed speed ratios which limit the travel of the GO pedal
Because these transmission work on balancing spring pressures, a misplaced tension spring on either the upper or lower belt will also cause it to run slow.

Thanks!
Pulling the break pedal up didn’t do anything.
I did find the manual online.
the upper drive belt looks pretty worn so I guess I start by replacing the belt and see what happens.
 

bertsmobile1

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Belts.
They must be replaced as a set
Buy original MTD belts or OEM spec belts from a mower store, not generic belts from NAPA
These belts are a different shape to standard V belts.
When the belts are off check that the sliding sheave can move freely up & down to vary the pulley ratios.
 
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I don’t have experience with riding lawn mowers but I would expect most would run at least 4mph right?
 
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Also, I found the belt that runs the mower deck comes off of the front pulley. Can this be tightened or does that belt need to be replaced as well?
 

tom3

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Take a look at that manual, usually some sort of retainer on that belt so it won't come off. Maybe just a rod located close to the pulley on each side.
 

Rivets

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If it were me I would be replacing all three belts, as you must remove the deck to replace the drive belts. A couple of suggestions if you decide to do this yourself. Removing the battery and case will help. There are two bolts on the outside of the chassis which you need to loosen, do not remove, which will make it easier to remove the drive belts. Get the rear end as high off the ground as possible to crawl underneath. I like about 8-10”. Get an assistant if possible, these can be a real bugger when you are doing it the first time. Patience will be your friend, so go slow. There are a couple of videos out there which may help you understand how to do it.
 

bertsmobile1

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Also, I found the belt that runs the mower deck comes off of the front pulley. Can this be tightened or does that belt need to be replaced as well?
This will depend upon weather you have an electric PTO ( pull a button ) or manual PTO swing a lever.
With the former the belt is always tight and the latter the belt has to go loose to allow the blades to stop spinning.
In any case changing all of the belts is always a good idea as suggested check the old drive belt against the new one for shape, cracks & wear.
Note V belts wear thin across the V.
While it is off spin all of the small pulleys, they should be smooth & QUIET, if not replace them as well.
So it would be a good idea to schedule the work over 2 weekends.
The most important tool in your tool chest is YOUR CAMERA take lots of photos ,
Belt run, Spring anchor points and note the clutch spring is handed & must go back on the same way
Also note the position of the tension spring on the top pulley ( big one ) under the seat.
The whole system is reliant upon this spring.
On some the big pulley needs to be loosened ( or removed ) because it uses the sides of the mower as belt retainers so the belt can not come off.
This is best done with a rattle gun.

We are here to help so if you post a few pictures of the set up we can can direct you through the process step by step and the best place to start is the ID tag under the seat.
The videos from "Taryl Fixes All" & "Donnyboy" tend to ne the most accurate & easy to follow.
When searching use both Troy Built and also MTD as MTD made the mower and the exact same mower is sold under a dozen different names .
 
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Thanks for all the replies!
I changed the drive belt, but I haven’t noticed any improvement in speed. It tops out at around 2-3 mph.
is that normal?
 
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