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I'm new to this forum, but not to lawn tractors. I bought a new Craftsman LT1000 lawn tractor in May 2005 for $900.

I do have a question. Lately the mower/blade drive belt has been slipping off (up) the idler pulley on the right side, the idler that gets pulled rearward by a cable to engage that belt. I can slip that back on by hand, but this never used to happen. So my plan is severalfold before next mow based upon what I read:
1. I bought a genuine spring 169022, think that spring was lost and I installed a too-strong spring.

2. Make sure that the mower deck is close to level or front edge is not more than 1/8 inch lower than the deck rear.

3. Bend the two guides closer to that idler pulley.

4. Try a new brand new belt.

5. Adjust the bracket (if there is an adjustment) to put more rearward tension on that idler pulley. It does have a new cable spring assembly there, my old one broke.

Anyway - I'm open to suggestions, thanks. I should say that both idler pulleys are new because the old ones had bad bearings.

Remove the deck and look for any cracks in the metal plates that attach the idler pulleys to the main deck shell. Also check for wear and tilting in the idler arm itself. It sounds like for some reason that when tension is applied it is allowing the tension idler arm to tilt forward allowing the belt to ride up over the pulley. As a repair dealer I have seen both situations occur on craftsman/poulan style decks.

tom3 said:

Does this idler ride on the back side of the belt? If it runs on the v-shaped front of the belt the pulley should be a V type, not a flat idler.

Click to expand...

The belt (on the right hand side, looking towards the front) has the V-side around the blade/mandrell pulley, then the flat side against that flat-surface spring-loaded idler pulley (#165888) then goes forward to the lower pulley on the engine.

Also, the belt seems to slip off over the little guide fingers more often if the deck is in a lower position. So the belt actually rides in an upward angle on that pulley (higher side towards the front of tractor) more when the deck is in a lower position.

Belts , like chains prefer to be run in a strait line on a single plane.
When ride ons first came out there were some very complicated systems to keep the out of alignment of the pulleys to a minimum.
These worked extremely well I service some mowers that in 20 years have never needed a new belt.
However people are too greedy & selfish to pay a reasonable price and too lazy & stupid to be able to see where their cheapskate attitude would lead.
So now days we have mowers with no out of alignment compensation for the deck belt on most mowers.
Most mowers are set up so the pulleys are in the same plane when the deck is set to the middle cutting height.
At the top or bottom settings the pulleys are at their furthest out of alignment and the belt run is at it's longest .
So at the top or bottom there is the greatest amount of forces that will cause the belt to jump off the pulleys.
When a belt jumps off a pulley is is damaged internally so from then will jump off easier till it gets to the state where it will not stay on at all.
On your deck the tensioning arm wears oval at the pivot and this then allots the retaining washer to eat into the arm.
This allows the tensioning pulley to flap around providing the perfect conditions for the belt to slip off the pulley.
The other biggie on that deck is a broken mount on one of the spindle housings.
For the same reason as height compensation being dropped for the deck belt, AYP went to a 3 bolt housing which saved a fortune in bolts & assembly time but made the spindle housing extremely frail.
I replace around 20 of them every season as compared to 2 Murray spindle housings in 5 years and none of the latter 4 bolt housings.
The 2 bolt housings crack through but it seems solid, till you engage the blades when it tilts and throws the belt off or till the blades start to work hard in long grass.
The belt keepers are not designed to stop a belt under extreme stress from sliding off the pulley.
Their job is to prevent a slack belt for jumping off when for instance you disengage the blades or the tensioning arm flaps a bit during start up.
Then you have the pulleys them selves.
Pulleys wear on the sides and the more they wear the more easily a belt will jump off and the faster a new belt will be destroyed as it has to run on the wear step rather than on the correctly shaped flat sides of the V groove.
Then the bearings do wear out, the grease dries up so while they will spin freely when cold, they lock up when hot then eventually pop the rivets out of the cage & collapse.
So any noise or notchyness from a pulley bearing means it needs to be replaced.
Finally the fixed idler wears on the flanges and it is those flanges that do all the work in keeping an out of alignment belt on the pulleys.

Then we get to the deck itself.
The splindle housings can warp the deck again putting the pulleys out of alignment.
Then the deck mountings wear which allows the deck to twist again causing the pulleys to be further out of alignment than the belt can tollerate

Re: Craftsman LT1000 lawn tractor mowing belt

Cusser said:

I'm new to this forum, but not to lawn tractors. I bought a new Craftsman LT1000 lawn tractor in May 2005 for $900.

I do have a question. Lately the mower/blade drive belt has been slipping off (up) the idler pulley on the right side, the idler that gets pulled rearward by a cable to engage that belt. I can slip that back on by hand, but this never used to happen. So my plan is severalfold before next mow based upon what I read:
1. I bought a genuine spring 169022, think that spring was lost and I installed a too-strong spring.

2. Make sure that the mower deck is close to level or front edge is not more than 1/8 inch lower than the deck rear.

3. Bend the two guides closer to that idler pulley.

4. Try a new brand new belt.

5. Adjust the bracket (if there is an adjustment) to put more rearward tension on that idler pulley. It does have a new cable spring assembly there, my old one broke.

Anyway - I'm open to suggestions, thanks. I should say that both idler pulleys are new because the old ones had bad bearings.

Click to expand...

Responses to above:
1. New spring didn't look too much different from the existing one, installed it anyway.

2. Deck was nowhere near the spec from front to back, was way too low in the front; I tightened the large nuts all the way towards the rear to get the correct tilt. I used never-seize lubricant on the threads.

3. Bent guides a little tighter.

4. I'm trying the existing belt which still looks OK.

5. That bracket cannot be adjusted unless I remove it and make slots from the round holes.

Also, I took off the two mandrel pulleys and lubed those mandrel bearings with light oil. I have two new complete mandrels but did not install those at this time, mandrels spun readily witthe added oil.

So did belt stay on??? Well, due to the weather, I did not have time to take for a test mow, maybe tomorrow.

Re: Craftsman LT1000 lawn tractor mowing belt

Cusser said:

So did belt stay on??? Well, due to the weather, I did not have time to take for a test mow, maybe tomorrow.

Click to expand...

Update: huge success. Mowed for 2 solid hours, belt stayed on, worked fine. I did make a modification to raise the deck deflector shield a little, helps with higher weeds, gets them out from under the deck.

So I think the tilt of the deck was the major factor, had never adjusted that, how it came from factory. Nothing in the owner's manual says anything about that being involved in throwing a mowing belt, or anything about throwing a belt anyways.

So thanks to bertsmobile1 and others who posted about the deck angle in other threads that I had searched previously!!!

Weeds were somewhat high this weekend. I had the belt slip off twice while using 3rd lowest setting of the six, changed to 4th lowest from the ground, didn't slip off at that setting at all, 1 hour of use. After mowing, cleaned out underneath and installed new blades, which were worn, and too far gone to re-sharpen. These are Arizona weeds, tons different than cutting a lawn....

Hmmm, that pile of deck cleanings sure looks familiar