troy bilt bronco new belts problem

bbisho123

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Hi Guys,
I have a bronco model number 13aj609g766 37746. not sure of the year. I have replaced all the belts. The small drive belt keeps popping off the pullies and the main drive belt is really loose. like its the wrong one. I have checked it against diagrams and it is the correct numbers. seems long.

any help or ideas will be apprieciated.

I did also tighten up the drive pedal linkage all the way and the belt is still very loose.
 

bertsmobile1

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Is the double pulley ( the variable one ) mounted in the correct place and secure ?
Very rare for the upper ( short ) belt to come off the pulleys unless the large pulley is bent or the vari pulley is loose.
All 3 of those pulleys are fixed so they never cone out of alignment unless the big one is bent or the tensioning arm is badly worn.
The lower belt is always loose till you put your foot on the go pedal.

Suggest you go through the following threads :-
https://www.lawnmowerforum.com/showthread.php/49864-New-Belt-to-long?highlight=varidrive+pulley
https://www.lawnmowerforum.com/showthread.php/46871-Another-Slipping-Pony?highlight=varidrive+pulley
https://www.lawnmowerforum.com/showthread.php/40077-Vari-drive-information-request?highlight=varidrive+pulley
MEchanic mark posted a link to the MTD manual covering the vari drives in post 2 of this thread

Once you get through all of them you will be a vari drive expert .
If you are still in the dark, hit the grey search icon and type "vari drive" as the search criteria.
Lots of threads there, mostly the same problem as you have.
 

bbisho123

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Thanks, im going to check it out today. There is is alot of slack in my large drive belt. The manuals you attached show a different model i think. I also think my top belt the spring maybe in the wrong location. I will check it out.
 

bertsmobile1

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There are a 1/2 dozen variations to the vari drive set up.
Basically it is the same as the stepped pulleys used to vary the speed on pillar drills & lathes.
Only difference is you have 2 infinately variable diameter pulleys in place of 3, 4, 5 or 6 individual steped sizes.

All of them work the same way.
A fixed tension in the short belt is worked against by you varying the tension in the longer drive belt.
The belt with the most tension runs deeper in the groove and forces the other belt to run further out thus increasing the belt speed ( in feet / min ) which turns the tranny pulley faster.
You can do this with a pedal, with a lever in the dash or a "speed selector" on the fender, the latter two give you fairly fixed speeds while the first is the same as a gas pedal in your car.

Because the tensions are quite big the springs wear through the mounting hook and wear thin themselves.
I regularly have to weld up a slot that the spring has cut through the mounting over years of use.
Also because the same frame pressing is used for dozens of different mowers, systems where the spring just goes through a hole can cause grief if you did not make notes or take photos before you start.
It gets even more complicated where a mower uses the same pedal for clutching & braking..
The clutch /brake pedal has to overide the gas pedal to make the long front belt to go slack otherwise you are breaking and accelerating at the same time.
 
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