i see that this is a big discussion about mtd and there vari drives well my mtd huskee has one and i did a pulley swap on the trans it had a 8" i think and i found a 5 1/2" and it works just fine just had to buy a smaller belt. and it is a monster in the mud bc if you want more "speed" you would just hold back the clutch and rip it up. but the problem i am having is i am always blowing the back belt. and i hardly blow the front one. i am running a 50"rubber b belt on the front and a 39"Kevlar a belt. and i cant see why i keep blowing belts.
Age : 66 Join date : 2014-04-14 Points : 4152 Posts : 491 Location : Index, Washington
First, here's a link to a YT video showing the operating principle of the Variable Speed Pulley system.
This is not the typical layout in most post 2000 MTD mowers [they use a rear belt arranged in a triangular setup, with the front just running straight down the center of the chassis]. This setup still shows the base method of operation; A moveable double-v pulley [I'll call it the VSP] with a sliding center disc moves toward and away from the driving [engine] pulley, and a spring loaded tensioner keeps the rear belt tight at all times, even with the 'clutch' pedal all the way in. The pedal is linked directly to the pivoting VSP bracket, and the 'shifter' switch on the dash/fender just limits its movement by means of a stepped bracket, fixing the position of the VSP and thus holding a constant speed. Clutch disengagement is only achieved because the pedal-in position moves the VSP so close to the engine that the front belt goes loose.
The most common problem people have with VSP trannys slipping is because of a worn/wrong rear belt, or a saggy tensioner spring. Hard 'shifts' or sticky feeling clutch is caused by the VSP unit seizing, probably because of sitting forever or just wear of the sliding disc. MTD original VSP rear belts work fine. Don't use the old rubber furnace blower belts you've got laying around. Belt width and length are imperative to proper shifting and tension. If a trans pulley swap is done, a different rear belt isn't needed, just modify the tensioner to suit the different trans pulley.
Possible modifications I can see to this system to make it more than practical in ATLT use is first, belly plates to keep trees/brush/water/mud/jenk out of the VSP. Then, as far as speed/pulley swapping goes, a larger engine pulley [will require a longer front belt] And a smaller trans-mounted pulley, as in any mower pulley swap. With VSP systems however, you have a max and min size for each pulley.
Consider 4.5" the largest for the front, and no smaller than 3" in the back. I run a 4"/4" and get a decent trail speed and slow enough crawl ratio in 'first' My tractor's a 2006 YardWorks 15.5/42 Tecumseh Formula. Same pulley sizes are generally the guideline for all off-road/rally mowers since the combo of speed/crawl is just right. Thing is though, MTD VSP trannys are generally geared a hair faster than a typical Peerless/Foote/Spicer. I'm sure you've noticed the speed some of these stock MTD's have compared to some hydros and gear trannys. BELLY PLATES ARE A MUST. KEEP THE VSP DRY/CLEAN.