MTD variable pulley

bus_driverSeptember 23, 2006

My 1990 38" MTD 12.5Hp Briggs has the variable pulley drive with lever that gives the various "gears". This mower has seen lots of use and the durability of this variable pulley has amazed me. It is apparently quite a good system. The belts on that pulley are the originals. I have not serviced that pulley at all. It now is not doing so well. When this mowing season ends, it will get careful disassembly and repair/replacement as necessary. New belts are no problem to find and the idler will be replaced also. But the variable pulley itself is sort of a mystery to me. Apparently no aftermarket supplier offers it, so if a new one is needed, I would have to get it from MTD. What about that pulley does/can wear? Bearings in the pulley replaceable as separate items? Tell me all you know about servicing this pulley? Price of new one?

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I have a later model variable speed pulley MTD, works great, and I am fascinated by it. While you are waiting for someone with some hands-on experience to respond, thought I'd share what I know.

I don't remember who it was, but I came across a web vendor who sells an MTD vari-speed pulley. As I recall price was in the $80-$90 range. If you need to buy one, I'd go directly to MTD to be sure you get the right one.

On my machine the vari-pulley appears to be two pulleys formed by three disks mounted on the same shaft. The top and bottom disks are fixed in position and serve as the top and bottom halves of the two pulleys. The third element is between the other two and is designed so it can move up and down on a vertical shaft.

The position of that middle element determines the pulley ratio. As the disks get closer together the v-belts ride closer to the ouside of the pulley; as the disks get further apart, the v-belts ride nearer to the center of the pulley. So this up/down movement of the center element changes the pulley ratio.

Again without ever having worked on one, it seems critical to keep the up/down motion of the central element free and easy. Doesn't seem like there is anything else likely to go wrong with it. If it's malfunctioning, it may be possible to clean and lube the shaft to make it as good as new.

Are you sure you don't just need new belts? If they stretch beyond a certain point, the system won't work. Belt tension largely determines where that middle element sits.


    Bookmark   September 23, 2006 at 6:47PM
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I have worked on these machines for years, and have found them to very reliable. The only repairs I have had to do is the bearings and centre post.This has been due to moisture getting into the bearings. Just get them from a MTD dealer and you wont have any problems.One point to remember is that it is a good idea to replace both belts, and to adjust the varible speed as per manual (if required)

    Bookmark   September 23, 2006 at 8:10PM
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I agree with both of you guys.
The design is so simple with very few parts and for hundreds less than a Hydro.
If Bus driver got 16 years of use out of his before any maintance , thats pretty good.

    Bookmark   September 24, 2006 at 5:04AM
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I can find no information about lubing the bearings. What kind of bearings are they? Are they replaceable separately?

    Bookmark   September 24, 2006 at 7:03AM
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They are thin needle bearings which can be puchased seperately, but if the needles are not falling out when
you lift off the pulley, then I would leave them alone,
just put a small squirt of grease in there and reinstall.


    Bookmark   September 24, 2006 at 9:07AM
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Bus_driver, I suggest you tell us what the symptoms are. Is it noisy, not shifting right, moving erratically or what? All you said in the OP is "It now is not doing so well."

Also, is your machine an MTD brand or is it another brand built by MTD? You may get more useful help if you let us know more.

Regarding the location of bearings, I suggest you begin by checking the Operator's Manual for your machine. My manual has detailed blow-up drawings for most components. If you don't have your manual, try downloading one free from the MTD web site. You'll need your tractor's model and serial numbers.

From the diagram in my manual, my 15-year newer TroyBilt by MTD has (two?) ball bearings in a bearing cup that's mounted to the bottom of the variable-speed bracket. The bearings do not appear to be accessible without dissassembly.


Here is a link that might be useful: MTD

    Bookmark   September 24, 2006 at 9:36AM
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wise_guy(NW MN)

All of the above information is very good.

Make sure that if you do replace the belts, that you use genuine OEM belts for this application. Most generic belts only come in 1" increments and do not properly fit this application. You'll be stuck with a circumstance of having either belts that are either slightly too long or too short.

Trust me -- I've been down that road.

    Bookmark   September 24, 2006 at 11:03AM
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If you have the part number from the owners manual exploded parts drawing, you can check prices on the mtd web site. My Huskee uses the "automatic" version, which appears to change the drive ratio depending on belt tension. Does anyone know if the "automatic" system is as reliable as the manual system? When operating the tractor I find it hard to keep the pedal position constant due to bumps in my lawn. Will this continual movement of the pedal result in increased wear? I don't notice any variaton in speed.



    Bookmark   September 24, 2006 at 10:38PM
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Red, if by manual system you mean the one with the speed selector lever, it too works on belt tension. The lever is nothing but a series of detents that holds the pedal in a "semi"-fixed position. You can always depress the pedal, which on the manual system slows the machine down.

I doubt there would be any significant wear from small or even large motions of the pedal in either system. Transmission wear comes from the high speed motion under load of the belts, pulleys, and bearings.


    Bookmark   September 25, 2006 at 12:58AM
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I guess while we are on variable drives ,where does a person check the gear oil level in the transaxle case?

    Bookmark   September 25, 2006 at 5:01AM
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It has a big squirt of semi-solid grease shot on the gear cluster before assembly, and no way to add anymore without


    Bookmark   September 25, 2006 at 7:53AM
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I have this same system and it will not disengage to stop or shift. I have replaced both belts and the center pulley seems to move freely. I can shift at will with the engine off but not when running. I can watch the belts move in and out at the variable speed pulley but the transaxle belt never stops even with the pedal fully depressed. How does the system disengage the belt to stop turning the transaxle ?

    Bookmark   May 11, 2007 at 7:28PM
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I have 4 MTDs and my pop owns an older MTD - all with the varible speed pulley setup. Its similar to a torque converter setup on like a snowmobile. Ive had great luck with the original setups, never had to grease them , one was 'stuck' on a 18.5/42 tractor i got for free, a few hits with a hammer freed it up nicely. I have a couple spares off a couple junk tractors, just in case i need another one, but since the running tractors are older then the junked ones, i dont seem to think i will anytime soon.

    Bookmark   May 12, 2007 at 1:28PM
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jerryo(z4 in SE MN)

dynamike59 asked:

while we are on variable drives ,where does a person check the gear oil level in the transaxle case?
I have a newer MTD (around 2002). I drilled a 1/4 inch hole near the center gear of the rear houseing. This ended up under the large tranny pulley, so access is not easy.
I found the tranny had gear oil in it. Apparently, MTD has dropped the bentenite (very stiff) grease used for years.
And yes, I plugged the hole with a rubber plug.
BTW. I should have know the tranny used gear oil as it was wet around the shift rod.


    Bookmark   May 12, 2007 at 9:56PM
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I have the automatic ,not the shift on the go model but the vari-drive principal is still the same.
The belt slips on the motor pully acting as the clutch.
When the belt tightens it starts to turn the lower and upper vari drive pullys.
When the belt tightens even more the lower pully spreads apart and the upper pully draws together ,giving you different pully ratios.
I would check to see if your foot pedal linkage is adjusted properly.
Also the vari-drive systems are very belt sensitive....did you replace the belts with the recommended factory belts?

    Bookmark   May 13, 2007 at 4:53AM
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Theres no fluid in the single speed transaxles. Theyre a sealed unit, packed with a heavy grease from the factory. Ive had 4 transaxles pulled totally out of different MTD tractors and there are no plugs to add/change fluid ( plus the fact is i asked a local longtime tractor guru and he told me aboot the grease from the factory.)Id be wary of drilling holes, metal shavings can get into the trans and screw things up. The best way would be to open the housing to be able to clean out the filings. More then likely most oil would drain out the axle shaft holes, since there isnt an oil seal there.

    Bookmark   May 13, 2007 at 5:01AM
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jerryo(z4 in SE MN)

kiddranger wrote:
Theres no fluid in the single speed transaxles.

Maybe you noticed that I said the old ones used bentonite.

Did you notice that I found gear oil in my 2002 model?

I don't know why they changed. I don't know if they changed back.

I do know that my parts manual shows rubber seals on the rear axles. but not on the shift shaft. And the shift shaft seeps.


    Bookmark   May 13, 2007 at 11:37PM
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Jerry O

I also see the axel seals (721-0338) in my 2003.
It is strange that the drive shaft doesn't have any seals, just flange bearings.
It looks like the unit could be filled to within 1-2" of the drive shaft flange bearings with gear oil alowing the differential gear and the bevel gears to dip into the oil for lubrication without leaking except on a very steep side slope.

    Bookmark   May 14, 2007 at 3:01AM
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My variable speed pulley on my 38" MTD seems frozen. My frond drive belt started to smoke when I tried to engage it into gear. After taking the belts off, it looks like the outer discs on the pulley won't spin. This seems wrong.

Can it be fixed? How do I get the pulley off?

    Bookmark   August 14, 2008 at 9:53PM
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I have a (2000) 42" YardMachines/ Model: 13AF660G352
It is "shift on the go" with the variable torque pulley...exactly as described by "Posted by jerryg_nj (My Page) on Sat, Sep 23, 06 at 18:47".
My pulley had a Snap Ring (.56" Dia.) retainer that rode on top of a plastic washer on the top side of the pulley shaft. You will need a snap ring pliers to remove it, but an inexpensive pair that has multiple pin sizes can be used.

    Bookmark   July 28, 2013 at 1:27PM
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We replaced both drive belts and now cant keep the variable speed belt on. It is the correct belt, Oscar Wilsons belt. PLEASE help. It has been put on about 15 times. I run it about 10 feet and it falls off. What gives??
Very upset dad...
Model 601 series
Belt # 754-0468

    Bookmark   September 5, 2013 at 3:27PM
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Why can't we start a new thread anymore? The most likely cause would be a seized or seizing idler pulley. It would be good to know also that the transaxle is securely mounted and that the brake is releasing. If we need to go further, please start a new thread w/ complete model number from below the seat and part #s replaced. I assume that you have installed the MTD brand belts as OW is an MTD distributor?

    Bookmark   September 5, 2013 at 9:59PM
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