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New CVT transmissions. Any experience?

Posted by tuckermaclain Nebraska (My Page) on
Wed, Jun 11, 14 at 22:22

Looking for a rider to do my small yard, just for fun. It's just a 1/2 acre but pretty steep slopes. Had wanted an X304, but JD cheapened them with a K46 recently. Thought I'd need a manual because of the slopes. Thought about a Wheel Horse. Looked at the latest AYP Craftsman, and they have a new General Transmission built CVT. I demo'd it and it pulled like an electric motor up a steep slope. Pretty powerful. Never heard of this. Heavier duty than the one MTD licenses. Reading the specs, it's got a bit more torque than a K58. It will run cooler. It is more efficient. Mantaining it should be replacing the external belt. There seems to be no down side to it. The AYP tractor cost me 1,600, which is a lot less than something with a K58. Before anybody tells me how bad AYP is--I like it just fine. For my needs it is more than adequate. Just cutting a little yard and pulling a trailer with mulch or shrubs. Does anybody have any experience or opinions on this tranny that they'd share? I've used torque converters in other things (minibikes, snowmobile) and they were wonderful and easy to maintain. I have a suspicion that Tuff Torq and Hydro Gear are going to make some or lose this market. Hydrostatics are in comparison inefficient, expensive, make lots of noise, and need regular (hard to do) maintaining. I feel pretty certain that they are going to the dustbin of history with lawn tractors.


Follow-Up Postings:

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RE: New CVT transmissions. Any experience?

They don't look like much from the outside, but yet I've not had a problem with one. The manufacturer used to have an interesting website that gave you more details. Wave of the future? We'll see....


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RE: New CVT transmissions. Any experience?

I took delivery of my Craftsman (AYP) mower. 22HP Briggs twin. 4x anti-scalp wheels, and the new CVT transmission. $1,725 with tax/delivery. On my steepest slope, where I wouldn't want to mow side-to-side, the thing pulls like a truck even with a trailer full of dirt. Other tractors I have had that used a hydro would never do that.
Looking at this forum, it seems like every third tread is about hydro problems. And, considering that the K46 is usually built as a throw-away tranny, and hydrostats in general demand a lot of mnx and care, is anybody else impressed or at least intrigued by the idea of a torque converter type of transaxle? They run cool, last forever, and mnx is easy enough that even your idiot brother-in-law could do it. I don't see ever wanting a hydro in a lawn tractor again.


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RE: New CVT transmissions. Any experience?

well, MacClain... your testimony sorta reads a bit like those written back when the first hydros came out in L&G power eqpt... and those hydros were designed/built nearly bulletproof. Then came the "cost improvements" aka competition wars, BBS outlets, low $$ price point customers, planned obsolescence, ad nauseum...
The CVT's are a sound design principle - just how they will fare in the rough and tumble of OPE over the next cuppla decades is a good question.


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RE: New CVT transmissions. Any experience?

***"torque converter type of transaxle"***
To be sure, the hydrostatic transmissions/transaxles you cite in your comparison...........ARE NOT torque convertor based mechanisms.
The variety of transmissions/transaxles found in outdoor power and lawn equipment are hydrostatic drive mechanisms, having a genuine hydraulic pump component supplying oil flow to an equally sized hydraulic MOTOR component.
The pump and motor are most often contained within a single housing or case, but that does not entitle them to "torque convertor" status.
The difference between hydrostatic drive and torque convertor is in the components.
Hydrostatic drive utilizes a hydraulic pump to create fluid flow.
The fluid flow developed by the pump is channeled to some type of delivery conduit to a control valve. It is the control valve that determines where the fluid flow will be directed to other hydraulic components. The components might be hydraulic cylinders (as is the case of a log splitter) or to a hydraulic motor (as in your typical hydro trans lawn tractor). The control valve also determines which direction the hydraulic motor will rotate.
A torque convertor is a highly modified "Fluid coupling".
Fluid couplings simply use fluid to (somewhat) connect a rotating power source member (drive member) to a rotatable power reception member (driven member). In fluid couplings, the ratio of input torque to output torque is theoretically 1 to 1 (1:1).
Fluid couplings have 2 members that deal with the fluid. The input power source member is called the impeller or input turbine, the output member is called the output turbine or driven turbine turbine.
Torque convertors have an additional member to deal with fluid flow. The additional member is called the Stator.
The stator DOES NOT rotate freely. The stator can rotate only in one direction because it rides on an overrunning clutch bearing.
It is the stator member that enables a torque convertor to "multiply torque" so that output torque is multiplied as much as 3 times more than input torque from the power source.
Graphically speaking, it works like this, using a common automobile transmission as an example.
At engine idle RPM, the torque convertor is unable to transmit enough power (torque) to cause the car to move because the fluid flow inside the torque convertor is insufficient to transmit the power from the input turbine through the stator to the output turbine. For this reason you are able to pull to a stop and leave the transmission in "gear" without killing the engine.
But, when you step on the accelerator, engine RPM increases and so does fluid flow within the torque convertor. The fluid flow caused by the input turbine TRIES to rotate the stator member in the opposite direction, but it can't because the overrunning clutch bearing holds it firmly stationary. At this point, torque conversion is taking place and torque output is greater than torque input, but still not great enough to overcome the mass of the car. As the engine RPM increases, the fluid flow volume will reach the point where the output torque is great enough to move the car, and then the output turbine begins to rotate and the car will begin moving. So long as the load factor of the car mass is very high, the torque convertor will remain in "torque conversion" and the stator will be motionless.
But, when the load factor of the car decreases as the car gains momentum and you "level off" to cruising speed, torque conversion tapers off and the stator begins to rotate along with the input and output turbines. When you let up completely on the accelerator, the stator then begins to rotate freely on the overrunning clutch bearing because the inertia of the car and its forward motion are at this point trying to "drive" the engine.
Most "modern automobile transmissions now feature a "lock up" torque convertor to make the connection between engine and transmission a "mechanical coupling" under "cruising conditions" to enhance fuel economy.


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RE: New CVT transmissions. Any experience?

My bad. By "torque converter," I mean the type that is found on a snow mobile or minibike--like the old Rupp minicycles. A good contemporary example would be the "Torq-a-Verter." It has two pulleys connected by a belt. The pulleys change size with engine RPM. I assume you know how it works. The General Transmission model has the ratios changed by pressure on a foot pedal rather than input pulley PRM. This allows the operator to "shift" through the entire range at any speed. A wonderful, simple idea that will make the hydro obsolete in this application. The automotive torque converter is not at all what I meant. All of the problems associated with the complex and relatively finicky hydro are a thing of the past. Just 2 pulleys and a fanbelt to worry about.


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RE: New CVT transmissions. Any experience?

I think you are referring to the Reeves drive pulley system, the most common type of CVT.

CVTS aren't the most efficient transmission out there, but they are a good economical solution. If the RS800 proves more reliable than the K46, I'll pick one up. I don't mind changing belts and pulleys.


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RE: New CVT transmissions. Any experience?

The Husqvarna website linked below, which I visited today, shows all those mowers with hydrostatic.
Do the mowers with CVT use the same rocker pedal arrangement? Since the blades need full engine speed, how does the operator select the ground speed with CVT?

Here is a link that might be useful: Husqvarna


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RE: New CVT transmissions. Any experience?

***" how does the operator select the ground speed with CVT?"***
I must be missing something here. What would imply that the engine RPM would drop because of having ground speed controlled by a Continuosly Variable Transmission?
The deck system still uses a separate belt for its power.


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RE: New CVT transmissions. Any experience?

Time and hours will tell if the CVT is more reliable than a hydrostatic. A viable alternative in any product line is always welcome.

Some people can break an anvil with a rubber hammer and while the K46 has its (minority) share of reported problems and usually from people who bought less tractor than they needed for what they do. Speaking to techs at TT I'm told that the number of complaints, warranty replacements, and parts sales for K46 hydros is a very low percentage compared to the number of K46's in the field and that, after all, is how they keep score. Sure, it'd be nice if those companies using the K46 paid an additional 50 cents or so to provide the lower case with drain plugs so the oil could be easily changed but then they'd need to add the external reservoir and that costs money too and the lawn tractor will cost more and the large majority of entry level LT owners probably would never change the oil anyway.

For me the K72 in my garden tractor is completely competent and doesn't act any differently when mowing or pulling a 600 lb lawn roller. I'm sure a K46 would leave its guts all over the lawn trying to pull that roller, but the K46 wasn't intended to do that yet I see people trying to pull lawn rollers, and a bigger lawn roller is better and only a few dollars more than a smaller roller, with entry level lawn tractors. After all, the roller will hook up to the lawn tractor so it should be able to pull the roller... right?

It's interesting to note that hydrostatics have been very well received in the short time they have been available in subcuts and cuts where they really work. Even die hard old timer tractor junkies I know who made the move tell me they would never go back to a geared subcut or cut.

While the RS800 may prove to be at least an alternative in an entry level lawn tractor only sporting 3/4" axles precludes it from use in a ground engaging garden tractor. Perhaps a future offering is a heavier duty version for GT applications.


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RE: New CVT transmissions. Any experience?

Where I work, we ordered/bought a brand new Kubota CUT last year because it was one of the few that still offerred a geared transmission. I agree that heavy-duty hydros are the way to go for most uses. In our case, we wanted a geared tractor because we use it primarily for spraying, and the geared versions hold a steady speed much better than any hydro units (very important for sprayer calibration). But for almost all other uses, a hydro would definitely be more convenient.

I think the biggest issue with the K46 is that almost NO ONE in the retail business will tell you that it is designed for cutting relatively flat lawns ONLY and not really meant to tow anything (and frankly, other than dedicated dealers, most retailers don't have a clue). Thus, the consumer generally ends up making an uninformed purchase.

In my case, I purchased a K46 tractor when I lived on a flat lawn, then moved to a new house with a hilly lawn. K46 started showing problems at just over 100 hours. I've traded out the fluid for some synth 5w50 and it seems to be working again. Now my debate is to sell it while its working or run it until it drops dead...it'd probably run quite a bit longer for someone with a flat lawn.

In the meantime, I need to think about a new tractor. My lawn is a little to big for a push mower (takes about 2-2.5 hours with a push mower), but can't justify spending $3k on a GT that can handle the hills. That's where the CVT would be a player. If it is at least as capable/durable as the K46, and repairs mean I need to replace a belt and/or pulleys, it would be a real contender. Belts are a lot cheaper than a hydro rebuild.


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RE: New CVT transmissions. Any experience?

I believe that CVTs have been used in snowmobiles and more recently in ATVs. I know Nissan uses them in automobiles. The only downside from an auto standpoint i've found is the towing capacity is terrible. In all cases, i've never heard anything bad about them. I figure they use them because they are probably cheaper then a regular auto transmission to build/maintain, but what do i know.


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RE: New CVT transmissions. Any experience?

Not sure I would trust Husqvarna's website - better to go to a dealer and see what they actually have - same with Craftsman. I don't know if their web developers are that inept or if they are just secretive about transmission offerings, but they sure aren't very forthcoming. If you can match up the Husqvarna with its Craftsman clone, you may be able to go to searspartsdirect.com and find the exploded drawings / parts list for that model and possibly determine the transaxle.


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RE: New CVT transmissions. Any experience?

Check the website below: RS800 replacement transaxle ($490) for certain Ariens, Snapper and Sears riders...actually, the only Sears rider listed comes up as a Canadian model. Some of the Ariens show up at HomeDepot, and have reasonably good reviews, although a few bad reviews on the transmission (again, no one really clarifies what went wrong with the transmission). What I was able to glean from it was that reverse tends to go out on these things, and possibly weak transmission mounts leading to bending of mounts and transmission subsequently throwing belts. We really need more in-depth info to determine if these issues are isolated, severe, or easily fixed by most DIY'ers...

Here is a link that might be useful: RS800 replacement transaxle


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RE: New CVT transmissions. Any experience?

RS800 tear-down video

Here is a link that might be useful: General Transmissions RS800 CVT tear-down


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RE: New CVT transmissions. Any experience?

My earlier post evidently was not clearly stated. When I mow, I use full throttle to drive the blades at maximum design speed. But that does not mean that I always wish the travel speed of the mower (in miles per hour) to be at a maximum.
So how does the operator of a mower with the new General CVT unit control travel speed independent of the blade speed?
With hydro, it is done with lever or pedal which adjusts the output of the variable displacement piston pump within the hydro unit.
With a Nissan Altima, a continued full throttle run results in the CVT going to ever higher ratios resulting in ever higher speeds-- within limitations.
So the mower is not like the car.
With the General CVT, is it a pedal, lever, or ?? And how is reverse selected?


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RE: New CVT transmissions. Any experience?

Looks as if this was posted by the manufacturer.

Here is a link that might be useful: General


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RE: New CVT transmissions. Any experience?

Well, from watching the videos and reading thru GT's webpage, I would say that the controls are very similar to a hydro, can either be a two-pedal setup for forward/reverse just like most hydro units, or can be a back/forth lever on the fender. However, I can't be 100% sure since I haven't seen one in the wild yet. But from website pics of Ariens models, that appears to be the case.

The video also suggests a variator, so I assume input speed remains constant and output speed can be "variated" or changed as needed. Proper mowing technique is to keep engine at full operating speed for the mower blades, while travel speed is adjusted as needed by the operator. Everything from mower blade length to deck design and standard engine operating RPMs have been designed around this scenario, so I can't imagine the CVT would change it.


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RE: New CVT transmissions. Any experience?

I went by Sears today. Turns out that the sales people are not especially well versed on the subject either. So after looking at the mowers displayed, both the sales person and myself now know more than before.
The two units on the sales floor in the store with the General CVT are among the heavier duty of the mowers offered. That may be a commentary on the expected durability of the unit.
The CVT has travel speed of 7.5mph. The control I saw is the familiar right foot rocker pedal. But it feels a bit different. It was not running when I operated the pedal.
Looking under the unit from the rear, the molded "plastic" housing for the differential ring gear is nearer the left rear wheel and the housing bottom is easily visible there.


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RE: New CVT transmissions. Any experience?

Interesting! Did you get the model numbers for those tractors? I'd heard the "fast tractors" were the CVT models, but no confirmation of that. Doubly interesting is that the Ariens models listed as having the CVT are also listed as having a top speed of 5.6mph, so I wonder if they are geared down more or if there is a typo somewhere. Gearing down would be preferable for work in hilly areas.


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RE: New CVT transmissions. Any experience?

Interesting! Did you get the model numbers for those tractors? I'd heard the "fast tractors" were the CVT models, but no confirmation of that. Doubly interesting is that the Ariens models listed as having the CVT are also listed as having a top speed of 5.6mph, so I wonder if they are geared down more or if there is a typo somewhere. Gearing down would be preferable for work in hilly areas.


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RE: New CVT transmissions. Any experience?

Tuckermaclain - Would you share the actual model number of the Craftsman mower you bought? I am looking for a new riding mower. Have bought Craftsman mowers for many years, but was concerned about some of the "new" features they are now offering. Liked your comments on the one you bought so would like to look at that one specifically.

Thanks.

Mary


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RE: New CVT transmissions. Any experience?

Ay Sears, some of the mowers now have a button to push for blade engagement-- as do some Husqvarna models I glanced at while at the farm store this week. I have never had a mower with electric blade engagement. It might be great but it seems to me to be a potential trouble source and the lever is not a problem for me.
Hope the CVT proves to be a durable drive unit. I am not planning to buy a new mower anytime soon.


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RE: New CVT transmissions. Any experience?

Interesting website.

Here is a link that might be useful: Found this


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RE: New CVT transmissions. Any experience?

Yesterday was in a sizeable, but not the largest, Lowes store in my area. Looked at the limited selection of John Deere and Husqvarna front engine riders on display. None of them had the General transaxle. But signage at one of the Husqvarna mowers boasted of travel speed up to 8 mph.


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