46" MTD mower deck breaks blolts and strips belts.

C

creedmoorbob

Forum Newbie
The return Idler pulley assembly on my 46" MTD Yardman Lawn Tractor deck bolts keeps breaking and the belt mower deck belt twist, comes off and or shreds. I have replaced the bolt 4 times and the the belt now twice. I reversed loaded the bolt (so that the threads come out the top instead of underneath)) and so far the bolt hasn't broken but there is a lot of vibration on the whole upper deck drive assembly and when I disengaged the deck drive the belt comes off or twist. Any one have a solution to this problem? I am thinking that the belt is riding too high on the return idler pulley...but there seems to be no adjustment for that.

Creedmoorbob

MTD Lawn Tractor 46" cut
760-770 series
 
WELCOME to LMF...

Check the blade spindles where they bolt to the deck... they may be cracked allowing them to tip slightly ... that can cause the problem you are describing..Everything has to be in line for things to operate smoothly... :smile:KennyV
 
You don't say how old this unit is, but I would also check for worn pulleys which may be grabbing and causing small cuts in the belt.
 
creedmoorbob said:
The return Idler pulley assembly on my 46" MTD Yardman Lawn Tractor deck bolts keeps breaking and the belt mower deck belt twist, comes off and or shreds. I have replaced the bolt 4 times and the the belt now twice. I reversed loaded the bolt (so that the threads come out the top instead of underneath)) and so far the bolt hasn't broken but there is a lot of vibration on the whole upper deck drive assembly and when I disengaged the deck drive the belt comes off or twist. Any one have a solution to this problem? I am thinking that the belt is riding too high on the return idler pulley...but there seems to be no adjustment for that.

Creedmoorbob

MTD Lawn Tractor 46" cut
760-770 series
Click to expand...
You likely have a bad bearing in one of the spindles or pulleys causing the pulley to intermittently seize which is putting too much drag on the belt causing it to shred. If a belt is coming off often but showing little wear that is likely that the front of the deck needs to be adjusted up to align itself with the crankshaft pulley or a misalignment elsewhere or a broken or bent belt guide. I had a problem with my MTD 46" breaking the idler shoulder bolt. I ordered a bolt, and it broke after a few mows. I examined the bolt and saw it was made up of cheap brittle composite metal. I ordered a couple of 2 1/2" long steel sleeves with 5/8" outside diameter and 3/8" inside diameter from Ebay. This 2 1/2 x 5/8" sleeve is the size of the shoulder on the brittle MTD bolt. I bought a quality 3/8" bolt 4 inches long. I greased and put the bolt through the sleeve and used extra-large flat washers at the bottom of the deck when I bolted it on. This is where most of the vibration comes from causing the brittle 3/8" threads to break as this is a shoddy design. I put the head side up with a couple of flat washers, but I am thinking about reversing it so the meat of the sleeve with no threads are at the bottom. But so far after a couple years the bolt hasn't broken and if it does break all I have to do is go to the Hardware and buy another 4' long 3/8' bolt. I have an extra sleeve in case the other idler shoulder bolt breaks. But so far it is holding up.
 
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