Some people are breaking belts from the belt rubbing on the threads showing on the 2 rear adjustment rods. JD fix is to cut 1/2” off of the threads. Well with my X300 I only have 5/8” of threads showing after I adjusted the deck properly using the gauge in the middle of the deck height adjustment knob. Yes that is the tool you lay on the ground. There are 2 vertical weld marks on the rear to where you set the gauge and for the front adjustment it’s just the middle point. The gauge should slide under with barely any drag. You may need something to pry off the gauge if it’s never been off before. My deck wasn’t adjusted from the factory.

I previously had a mower repair shop for many years. My neighbor broke 4 belts and asked me to look at it. Nothing was obviously wrong, but the last belt he installed didn't break but was shredded along the top of the belt after 10 minutes of cutting. Sure enough, the idler pulley you are showing was catching the top of the belt where the belt goes forward to the PTO. It also made a loud bang when you engaged the blades. I put 2 washers directly under the shoulder bushing and the banging on blade engagement ceased, but the belt was still close to the top of the idler pulley. I put 4 thick washers raising the pulley at least a quarter of an inch. The belt looked fine after mowing about 3/4 acre. The design really sucks and I see many people online with the same complaint. Local John Deere was no help to the neighbor. As you stated, your fix don't sound like it would solve the problem, but I think you nailed it. You really have to look at that belt when the belt and deck are installed and run it to let it settle where it wants to track on the idler. Then look closely from the right side of the deck at your normal cutting height. It's not an easy catch, but the top edge of the idler was super shiny and the bottom edge dirty. Thanks for the tip.

I broke 3 or 4 belts before finally looking closely at the belt tensioner bar that has the pulley mounted on top and the mount bolt through the center. It had just enough play to allow it to dip down and snap the belts shortly after startup. Replaced that and no problems since, just a reminder, take your time and look closely for play at each component because it does add up cumulatively to create enough to cause issues.

I've been thru this. The couple units I have in my shop do the same thing...break belts for no reason. All the holes for idler and tensioner pullies are not oblong. No slack in the tensioner arm. New pullies. New bearings. New tensioner spring. Both units broke brand new JD belts and the better Gates Blade Runner belts. I found that the OEM blades JD puts on these units are too heavy for the 1/2" belt used on it. Look at all the commercial units that have heavy blades like this X300 and they all have 5/8" belts. I decided to throw a 5/8" belt on it instead....I used a Gates 6767BR (5/8" x 147") and have had zero issues since. Thought I'd come on and leave a note for someone in the future. Hopefully they will see this.

My mother in law has an older John Deere that keeps throwing and breaking belts. She's had friends of friends try to fix it. I think I'll bring it to my shop and take a look at the pulleys. Thanks for the info.

thanks been breaking belts 3xs a year ready to buy a goat

Just went through this problem and the dealer (who was totally befuddled by this problem) replaced pto clutch and no more breaking belts!!! They had replaced pulleys and everything that could possibly be causing this breakage. My original belt was 8 years old (not broken) when I decided maybe it was time to replace and that is when the problem started!!

Looking at the product manual, the area that you focused on is supposed to be lubricated regularly. I am curious if not routinely doing this maintenance procedure caused the oval shape to form under the spindle. I will have to check this out on my own deck. Thank you for the follow up!

I have a John Deere x300, and have replaced 26 deck belts!

Excellent video, thank you. Here it is 6-14-23 and tall grass and lack of time for maintenance is winning. I have 42C 'convertible' deck on an LX277. Can you tell me what size belt it needs. I thought it would tell me that somewhere on the deck! Where is your shop? Be happy to pay for the help.

Have the same problem put a new belt on last week didn't even last mowing my yard and the leveling screw has the threads wore slick on the same side you fixed in the other video should I do the washer on the pulley to you think

My dad got a x300 John Deere and we replaced the mower belt about almost every time we mow and it’s getting annoying. And I don’t know what the problem really is.. but I think it’s in this video is probably the problem. But I will definitely show my dad this video and see if that’s the problem because it’s breaking the Belts clean. So do you think that’s the problem @J La?

Great job.

Thanks had the same problem

check the rear deck hanger bolt, on 1 side of the deck it is too close to the belt, and it rubs the belt, this may cause the belt failure

I see that hole is oblong. I'm just wondering why that happens? The bolts job is to hold the idler pulley. The bolt shouldn't be turning just the outside of the idler! Do you have a theory on how the hole got oblong?

2 excellent videos - a few questions. Video 1 (hanger bolt rubbing) : Is there any other way to fix the hanger bolt issue without welding an extension? That may be beyond my level. Will it fit on the outside of the bracket instead of the inside? In video 2 (update) you simply disassembled the pulley and added washers. One above and one below? Would you try one fix first before the other?

When the blades hit something, the weakest point in the deck, is the belt. Keep the deck a little higher and miss those obstacles.

I'm sorry.. this is a different deck with a different problem?

Thank you.

Congratulations! You succeeded in confusing everyone.

Mine is shredding the belts I'm on the fourth one this year ive mowed 3 times

Everyone is missing the obvious, a bad batch of Chinese belts.