Belt & Pulley problem for Craftsman LT1000

Discussion in 'Mechanic and Repair' started by krankshaft, Jun 30, 2008.

  1. krankshaft

    krankshaft LawnSite Member
    Messages: 2

    Craftsman LT1000, 18hp, 42" mower
    6 speed transaxle
    Model 917.273399

    After about 20min of mowing the mower sounded a bit louder. A few minutes later vibration, smoke, and a rubber smell comes from the mower area, along with a decrease in engine power.

    Upon inspection I found a thin rubber coat around the top end of the movable idler pulley that tightens the belt to engage the blades. Also, I discovered that this idler pulley would not spring-return to it's forward position without assistance. I sprayed some WD40 on it and it now returns like normal.

    A few more tests, the belt continues to vibrate along with a power loss, but without smoke & rubber smell. The engine itself is fine, and this only happens when the blades are engaged. It actually starts to vibrate when the mower clutch is half-way engaged. Upon disengaging the blades, I've noticed the blades take a little longer to stop as if it had more inertia than it should or something. And also this is when the V-belt vibrates the most and once came off the movable idler pulley.

    The manual says the V-belts aren't adjustable. I replaced the belt, and have the same results. The idler pulleys spin freely and the mandrel pulleys both have an equal tension. Did not try to spin the engine pulley, but I think it's ok. This has never occurred before and I've never done any maintenance for the mower section except replace the blades. They were replaced at the beginning of last summer. Any help is appreciated. Thanks!




  2. Jay Ray

    Jay Ray LawnSite Fanatic
    Messages: 6,510

    This probably is not it, but your photo with idler pulley engaged shows a belt guide that possibly could be in contact with the belt.

    Also, if it has a blade brake that contacts a pulley, that could be a source of heat build up on the belt.

    I have a Toro that used 3/16" round bar for snubbers to control belt vibration and the snubbers were eating belts. I located two flat pulleys in proper position to replace the snubbers and the belt is smooth as silk now.

    Hope it is an easy one.
  3. olde_blue

    olde_blue LawnSite Senior Member
    Messages: 349

    When your belt was slipping, it probably burned itself a thin in a few places. When these thin places pass over the pulleys, they can cause vibrations. Take off the belt and carefully look along the A (or "V") section to see if it is uniform in width along the whole length. If it is not uniform, you will need a new belt.
  4. jkason

    jkason LawnSite Senior Member
    Messages: 546

    Also check to make sure that the pulleys on the spindles spin freely (no bad bearings).
    And make sure you have the correct belt. Looks way too loose when engaged.
  5. DCTractor

    DCTractor LawnSite Member
    Messages: 3

    The correct belt number for that machine is 144959. The belt tension is not adjustable. Check your blades, make sure they don't wobble up and down. If they do your mandrel bearings have gone bad. Also make sure that the flat idler pulley doesn't wobble around. It is alright for the plate it is mounted on to have some up and down play as long as it isn't wobbling itself.

    In your last picture you say the PTO is engaged, but it looks like the mandrel pulley brake is still on the right pulley. When you engage the blades, are the brakes lifting off both pulleys?

    If all else fails, run your fingers along the belt and feel for any exceptional smooth spots on the top and bottom. That indicates burns and every time one of those burns contact your pulleys it will slip causing excess vibration in your deck.

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