How To Replace Belts On MTD Varidrive
Adams74Chevy emailed me and reminded me that I'd mentioned a while ago that I had a procedure for replacing the drive belts on the MTD Varidrive. So with Adam's encouraging I put it into words here.
The procedure apparently exceeds the 10,000 characters allowed for a post here, so I'll break it into 2 parts. Here's the 1'st part:
The MTD Varidrive uses 2 special V-belts to transmit power from the engine to the Variable Speed Pulley (VSP) and from the VSP to the Tranaxle.
When working correctly, the Varidrive system is smooth and simple. But it does tend to eat belts. So the bad news is, eventually just about every Varidrive owner will eventually experience the joy of replacing the drive belts, usually once every year or two depending on hours of use. The good news, it really isn't very hard to do.
This procedure assumes a basic mechanical ability and that you're generally familar with the internal layout of this tractor.
PARTS / TOOLS NEEDED: The belts of course: MTD Part Number 754-0280 for the front, and 754-370 for the rear.
It's recommended that OEM belts be used in the drive system. Generic aftermarket belts CAN be used, but their service life will be substantially less than the MTD belts.
10mm wrench, 8mm wrench, C-clip pliers, Adjustable Crescent wrench, and bearing grease.
If you have access to 'mechanics gloves', they'll be helpful here because they avoid the inevitable scratches and dings on your hands from sharp things inside the chassis.
Contrary to some beliefs, it isn't necessary to flip the tractor over to change the belts. It can all be done with the tractor upright.
It also isn't necessary to remove the mower deck to change the belts. However, access to some areas of the tractor chassis may be easier with the mower deck removed. If you were planning to do any service to the mower deck, this might be a good time to go ahead and remove it.
For safety considerations, disconnect the battery. This avoids the possibility of not only unintentional engine cranking, but you'll be handling metal tools around in the vicinity of the starter solenoid, so it's a good idea to take this saftey step. This might also be a good time to remove the battery and clean it and check the water levels and charge it up, as needed.
It will be necessary to remove the mower deck drive belt from the lower pulley on the engine crankshaft. Raise the mower deck to the 'Blades Off" (highest position). This makes the drive belt loose. Gently slip the belt off the left spindle pulley, then slide it off the lower engine pulley, and tuck the belt loop back out of the way. It may be necessary to remove or slightly bend away the Keeper Pins from the front Belt Guard in order to take off the deck belt. These Keeper Pins are positioned near the outside of the belt so as to keep it on the pulley when the belt is loose in the Blades Off position.
Next step, go to the top of the tractor and unscrew the shifter knob from the F-N-R shift lever. Then unscrew / unbolt the two fasteners holding the top plate on the transmission cover, and remove that plate. Now you can look down inside the chassis and see the main components of your drive train.
REAR BELT REMOVAL:
This procecedure presumes both belts are to be changed. The rear belt undergoes a lot more flexing than the front belt, and it's been my experience that the rear belt will need replacing about twice as often as the front. The rear belt must come off first, then the front belt can be accessed.
The diagram at the bottom of this document shows the primary components in the Varidrive system. The Variable Speed Pulley (VSP) [F] is the heart of the Varidrive system. A detailed discussion of how the Varidrive functions isn't the intent of this document, but for now it's sufficient to say that it's function depends on a variable tension between the front and the rear belts. The main source of this belt tension is an idler pulley [E] riding on the rear belt. The spring tension on this pulley, plus the fore-aft position of the VSP, determines what effective 'gear ratio' is delivered to the transaxle.
Proceeding with removal of the upper belt, it will be necessary to loosen and move aside the bracket [H] holding the shift lever. This bracket is held in place by two 10mm bolts which are accessed on the chassis wall under the left rear fender. It's sort of tricky to reach around the tire to get at these these bolts. I haven't had to remove the left rear wheel to access these bolts, but there are times when I wished it was off. Your call.
Next, place the Speed Selector lever (on the right rear fender) in 7 (highest gear). This will have the effect of moving the VSP carrier fully to the rear of it's travel, which reduces the tension on the rear belt. An assistant may be helpful for the next step. Grasp the Tensioner Pulley [E] and pull it against the spring tension (away from the belt) while you or the assistant slips the Rear Belt [I] off and over the top of the Tensioner Pulley. You can then gently let the Tensioner Pulley return to where it will come to rest in contact with the large Transaxle Pulley [D].
Using a pair of C-clip pliers, remove the C-Clip from the top of the VSP shaft. This will allow the VSP to be lifted slightly, which will give some extra clearance for the belt.
Slip the Rear Belt off the top pulley of the VSP, and then off the Transaxle pulley. It may be helpful to lay down at the rear of the tractor and look up under the back wall of the frame, so as to see how the Rear Belt comes off the Transaxle Pulley and clears obstructions. Lastly slide the Rear Belt behind the Shift Lever Bracket [H]... and now you'll be able to pull the belt all the way out of the tractor.
With experience, you can do this in about 15 minutes just to remove the Rear Belt. If you were only changing the Rear Belt, here's where you'd jump to putting in the new one. If you're replacing the Front Belt too, then continue.
FRONT BELT REMOVAL:
With the Rear Belt off, you'll be able to get the Front Belt off the VSP. I recommend servicing the VSP bearings at this time, since you'll have everything removed and accessable.
Place the Speed Selector lever in the PARK position. You should see this action move the VSP position forward, and this will reduce the tension on the Front Belt.
Next we'll remove the Front Belt from the Engine Pulley. This requires removing the Belt Guard [G] which held the Keeper Pins we moved earlier. There are 4 bolts either 8mm or 10mm (depending on model) which hold the Belt Guard in place.
With the bolts out, the Belt Guard will come down and foward out of the chassis. Now the loosened Front Belt can be slid off the engine pulley.
It isn't necessary to remove the engine pulley in order to change the belts. However this is a good time to inspect the inner walls of the pulley to check for excessive wear or pitting. Any rust pitting should be buffed out gently, to give a smooth surface for the new belt. And the pulleys can actually wear out. They work in a rough environment -- high speeds, high loads, and grit can make the pulley inner walls wear down, such that a new belt might not last long with them. Inspect accordingly.
Some models of the tractor have an extra Idler Pulley [C] on the Front Belt. It seems to depend on the engine -- twin cylinder tractors usually have this pulley, and singles seem not to have it. If it's present on your tractor, it may be necessary to loosen and remove it to allow the Front Belt to come off. It's a simple single bolt through the chassis floor.
At this point you'll be able to lift up the VSP on its shaft, enough to allow the Front Belt to be removed from the VSP. It may be necessary to adjust the Speed Selector position to locate the VSP away from chassis parts. I have usually had to loosen / remove another Keeper Pin mounted on the VSP shuttle -- you will see clearly what is required to get the belt off. With the Front Belt off the VSP, it can be pulled out of the chassis.
SERVICING VSP BEARINGS:
The VSP has a difficult life. It's worth inspecting this component now. You can lift it off the spindle, keeping careful track of shims both on top and below. The center disk should spin around freely, and slide back and forth freely. There should be no rust on the inside of a recently used VSP, although some slight rust is often seen on those that have been sitting for a while.
The entire VSP should spin freely on its spindle with no grinding detected by ear or by hand. The bearings can be replaced if necessary. If the bearings look good, relubricate them with high-temp automotive grade disk brake wheel bearing grease, and reinstall the VSP, keeping track of the shims. Don't get grease on the inside of the VSP. Don't reinstall the C-clip until later after the belts are back on.
INSTALLING NEW FRONT BELT:
I've always hated it when a manual glibly says 'Installation is just the reverse of the disassembly procedure.' Actually in this case that is fairly true, but we'll go through the steps anyway.
Thread the new Front Belt under the chassis in general position. Adjust the VSP shuttle for optimum clearance in the chassis, and lift the VSP slightly on its spindle. Loop the Front Belt first onto the top pulley (it's easier that way), then thread it down to where it's seated in the bottom pulley. Move the VSP shuttle all the way forward (PARK on the Speed Selector), and thread the front of the belt onto the upper engine pulley. If you loosened / removed the Idler Pulley [C], reinstall it now.
Reinstall the Keeper Plate [G], but not the Keeper Pins yet.
INSTALLING NEW REAR BELT: (continued in next post)