Shop Products
Houzz Logo Print
jfw432

Hydrostatic vs belt and pulley automatic

jfw432
13 years ago

I'm trying to figure out the difference between these two transmissions. I understand both operate in a similar fashion as far as the operator is concerned. While one takes a belt form the engine to control a hydraulic pump to drive the wheels and the other takes a belt to drive a varying wheel to drive the wheel like a CVT transmission in a car.

I understand the belt and pulley automatic is far less complicated. However, what is the real difference between the two? Is one more sturdy than the other? How much maintenance is involved with them? Can both withstand the stress of going up and down hills all the time?

Comments (26)

  • mownie
    13 years ago
    last modified: 9 years ago

    jfw, your inquest almost answers itself in the points you bring up:^)
    I'll give my slant on the subjects at hand, and add a bit of complexity to your description of the works.
    Hydrostatic drive power transmission: Uses an engine driven (usually by belt) hydraulic pump to power a hydraulic motor. The hydraulic oil flow is managed by a control valve that adjusts the volume of oil flow through the hydraulic motor to vary the ground speed of the tractor. Increasing the volume of hydraulic oil flow through the motor increases the ground speed. The control valve is a "double acting" (aka directional) valve in that the direction the control valve is moved from the neutral center position determines which direction the hydraulic oil flows through the hydraulic motor. Reversing the direction of hyd oil flow through the hyd motor reverses the direction of travel of the tractor.
    Advantages of hydrostatic drive are: Very smooth when adjusting ground speed or changing direction of travel.
    Because there are no gears involved in changes of ground speed or direction of travel, you will never have to "hunt for" another gear shift notch, or tease the transmission into letting you engage that next gear (sometimes accompanied by gnashing or grinding of the gears inside a manual gearbox tranny).
    Drawbacks to hydrostatic drive are: Actual transmission of power from engine to to where the drive axle shafts turn is less efficient than CVT due to internal fluid leakage in the pump, valve, and motor. This loss of efficiency tends to get worse as the three major components accumulate wear. The efficiency is also affected by the temperature/viscosity/ of the oil, and the state of degradation the oil is in at any given moment.
    Another drawback is that hydrostatic processes generate a lot of heat which must be shed (hence the fan on the input pulley) or the build up of heat will lead to foaming and burning (carbonizing) of the oil inside the transmission. When the oil foams, hydrostatic processes diminish or stop, and so does the tractor.
    Maintenance to the typical modern hydrostatic drive transmission is an adventure in creativity, and a challenge for the owner because marketing trends by the OEMs have made this genre "throwaways".
    Oil changes on many of these hydro units require the transaxle assembly be removed from the chassis and literally "turned upside down" over a catch pan in order to drain the oil. Few of them have an external filter for easy replacement, many have an internal filter which require opening the transaxle case.............not exactly what I call "routine maintenance".

    The variable belt drive, vari-drive, or CVT transmission is "a transmission" in and of itself, sort of.
    The CVT portion of the power train allows for a fixed range of RPM reduction between the engine crankshaft pulley (CVT input pulley), and the CVT output pulley (belt to the transaxle housing input pulley).
    The ratio of input RPM versus output RPM is contolled by the operator through a linkage system.
    The lower the output pulley speed, the slower the ground speed....but with more TORQUE applied to the axle shafts.
    The higher the output pulley speed, the faster the tractor moves across the ground......but with less torque applied to the axle shafts.
    Because the CVT pulleys adjust the ratio within a limited range, typically the transaxle has a manually operated gearbox to give a wider choice of ground speed and wheel torque combinations. The manual gearbox also provides for the change in direction of travel (forward and reverse).
    Advantages of CVT are: More efficient in actual power transmission (when belts are in good order).
    Heat build up in the transaxle during use does not decrease the efficiency or performance of the transmission system.
    Drawbacks of CVT: Expect to replace both belts at about 2-3 year intervals.
    Belt replacement can be in the neighborhood of $80 to $100 for the pair because you need to use OEM belts (which are naturally more expensive than generics).
    Because there is some "shifting of gears" involved in the manual gearbox when going between forward and reverse, there will be times when the transaxle gears don't "line up" exactly and you will have to hunt for the engagement sweet spot, sometimes a frustrating event.

    As I stated, those are my opinions.

  • Greg Goyeneche
    13 years ago
    last modified: 9 years ago

    There are some operation similarities between a hydrostatic transmission and CVT (Transmatic). I have bought and sold a lot of gear and transmatic lawn tractors, and fewer hydrostatics, but have had enough of each to form some generalized opinions. A similar application for CVT are snowmobiles, although they differ by using integral centrifugal clutches, a special type of belt, and both pulleys are moveable to provide variable ratios.

    The Transmatic is almost unique to MTD (and the hundreds of private labels they manufacture for). Deere used to use a similar transmission (Variator), but other than a rear engine rider, don't use much any more to my understanding. In operation, there is a clutch between the engine and CVT pulleys which slackens or tightens the first belt. There is a speed range control which sets the maximum speed ration, and there is a forward-neutral-reverse control on the rear axle. The rear axle is separate from the CVT and connected by a second belt.

    The hydrostatic is either directly coupled to the engine (higher end equipment) or belted to the engine using a clutching pulley (similar to the transmatic). The hydrostatic consists of a hydraulic pump closely coupled to a hydraulic motor which then drives through a differential to the rear wheels. The main operational control is either a hand lever or footpedal which controls both forward-reverse direction and ground speed. This is accomplished by controlling both the direction of flow and the amount of flow internally to the hydrostatic transmission. The clutch on a belted unit is used for starting, but the engine can continue to run with the transmission in neutral.

    I find the hydro easier to use, particularly if it is direct connected and has foot pedal control. No brake is usually needed (other than parking) because the hydro functions as a retarder when in the center (neutral) position. In fact, it's almost impossible to roll a hydro around not running, and most mfgs put a bypass on the hydro for this reason. With the transmatic you use the clutch to get underway, the machine then starts in the lowest gear (pulley ratio) and then advances to the tallest ratio limited by the speed control. To come to a stop, you depress the clutch which also actuates the brake, and then start process over. If you want to slow down to a lower "gear", you need to clutch and allow machine to slow and then select a lower "gear".

    Both transmission types are pretty well proven. The hydro is popular but not good if overloaded or used for ground engaging equipment. Excessive heat will wear out a hydro with expensive results. Also, hydros do not tend to hold up well in hilly operation. Hydros fitted to true, heavy duty garden tractors and CUT's are meant for this service and perform much better. The Transmatic is generally pretty simple and robust, although they tend to go through belts. Also, the rear axle on an MTD Transmatic is made by Peerless and can be the weak link.

  • wheelhorse_of_course
    13 years ago
    last modified: 9 years ago

    There are plenty of hydros that will handle ground engaging equipment. Wheel Horse tractors from the 1960's prove this.

    It is true, however, that under abuse the hydro will be expensive to fix (even those units designed for repair and maintenance) where as the CVT will usually only need new belts (though the wear and tear may affect other portions of the tractor).

    Incidentally, the continuously variable transmission concept is making its way into more and more automobiles!

  • mower_mitchells_org_uk
    12 years ago
    last modified: 9 years ago

    Hi, I am hoping that one of you knowledgable posters might be able to give me a bit more insignt into how transmatic works: my old MTD Lawnflite now only goes slow or slightly slower and I can't see what's wrong.
    The two relevant belts look in good condition (though I would see if one were stretched) and the linkages seem to do the right thing: the "variable speed dual pulley" (as MTD call it) sits in a different position front-back depending on the gear lever position. The tensioner keeps the rear belt tight. But this makes we wonder what actually changes the gear ratio: should the dual pulley centre section be moving around? I am not neccesarily looking for a remote fault diagnosis: hopefully if I can understand better how transmatic works I will be able to see what is wrong.
    Thanks, Angus

  • mownie
    12 years ago
    last modified: 9 years ago

    The ratio change is affected by the centre section of the dual pulley.
    The centre section must be free to to move up & down when the machine operator moves the ground speed control to speed up, or to slow down the machine's rate of travel across the terrain.
    The movement of the centre section of the dual pulley assembly alters the "apparent diameter" of each vee groove.
    The 2 belts are: Drive belt..........carries power from engine pulley to input groove of dual pulley.
    Driven belt........carries power from output groove of dual pulley to the gearbox input input pulley.
    Which way the operator moves the ground speed control will determine whether the dual pulley drive belt groove becomes smaller diameter, or larger diameter. When the drive belt groove "apparent diameter" becomes smaller.......the driven belt groove diameter becomes larger (and vice versa).
    When the ground speed control moves the centre section of the dual pulley to make the drive belt groove a small diameter, the ground speed of the machine will be slow, but the torque output to the axle shafts of the gearbox will be great.
    If the speed control moves the centre section of the dual pulley to make the drive belt groove a larger diameter, the ground speed of the machine will be great, but the torque output to the gearbox axle shafts will be low.
    By design, the 2 belts are a "matched set" to the specific application and when renewing belts, both belts should be replaced as a set.
    The centre section of dual pulley literally "forces" the belts to assume the changing diameter, so every bit of wear to the vee grooves, and to the sides of the belt vee will have an effect on the ground speed and torque output parameters of the machine.

  • gdj204
    12 years ago
    last modified: 9 years ago

    OK, I know little about CVT transmissions, although I've driven a few snowmobiles. The snowmobiles and autos that use CVT do not have gears, except for F/R in the case of the auto. Both types of vehicles operate in a much greater range of power and speed than a typical lawn tractor. Therefore, why does a lawn tractor need more than one gear (other than F/R) in a CVT?

    I can't imagine it is a power issue, since snowmobiles have a great range of speed with not much more power. Since lawn tractors are pretty much limited to a top speed around 5-6mph, that should free up the CVT designer to give it a lot more torque to the axle for the given engine HP. Any CVT experts care to respond?

    I, too, mow in hilly areas, and it frustrates me that I have to spend twice as much for a lawn tractor (over the base models) just to get a "reliable-enough" hydro tranny that can handle the hills. You'd think there'd be a better mousetrap out there...

  • earthworm
    12 years ago
    last modified: 9 years ago

    So, I'm thinking that the bottom line is this..
    The hydrostatic is great, but the good ones must have a way of changing the hydraulic fluid and the filter....And it
    will be less efficient that the CVT..
    The greater efficiency will come at a prive...every 2-3 years $100 to $200 for two new belts.
    Here, the DIY is worth $100.
    So, when buying, ask this
    1 hydrostatic, is the oil and filter changeable ?
    2 CVT, the the belts available right now ?And are they changeable and not a federal case)...
    And the responses were great and very informative.

  • justalurker
    12 years ago
    last modified: 9 years ago

    It should be noted that millions and millions of hydrostatic L&G riders are sold that are trouble free. The misconception that hydrostatics in entry level riders often fail is based on a very small (representative) number of posters complaining. People who are out mowing on their riders seldom post that they are working well.

    My experience is that hydros in entry level riders fail most often because they are intentional or unknowingly abused by the operators by asking them to mow too large an area, too hilly an area, pull more weight then they are designed to pull, pulling accessories that they are not designed to pull, and then there's the way oversized operator.

    John Deere warrants their X300 lawn tractor for 4 years or 300 hours and it has a sealed, non-servicable Tuff Torq K46 hydrostatic transmission. If those transmissions were so unreliable think JD would warranty it that long?

    CVTs look great on paper and work well in snow mobiles but the dust and dirt mowing environment is a bad environment for CVTs.

    There are a great many utility and sub cut tractors around here with most owned and operated by old timers who know tractors. Talking to them over the years they were belly laughing at the though of hydrostatics on real tractors till they got to try one and now there are very few who don't own hydro sub cuts and utility tractors with the most common comment... should have done this years ago.

  • earthworm
    12 years ago
    last modified: 9 years ago

    Excellent discussion.
    I wonder, does the Craftsman "tight turn" tractor's transmission cut the power to one wheel when the steering is turned full crank ?? I suspect that the Sears salesman may not know this...even Sears may not know this....
    I visit their site and the info is vague and missing...
    Kerry's on the Trindle Rd, Mechanicsburg is the answer ??

  • Sean Jankowski
    8 years ago

    I'm at witts end if I should get a hydrostatic machine or one with belts..

  • rexlex
    8 years ago

    all else equal... flat ground, hydro, hilly ground, belt. The "sealed at mfgr's" type hydro trannies just won't take the hill loads as well as the CVT's.. jmho.

  • krnuttle
    8 years ago

    Don;t over think the problem. I have a JD LT 135 with a Hydro transmission it is 15 years old and still going strong. For the last four years I have been mowing about a 1/2 acre. It varies about 20 feet in the 100 feet width. about the same in the 200 foot length. I have a road grade ditch in front of the house that is part of my yard and I keep mowed. While I can go up and down all of the grades in the yard, the best approach is to mow along the grades, not up and down the grades.

    When you are mowing in those tight spots around trees, flower beds, bushes, etc. you will enjoy the convenience of the no shift hydro.

    As said above those without problems are out working in the yard, mowing
    pulling small trailers, etc. Those with problems are on this forum.

    PS: it has been raining here for the last two weeks, and the yard is quite soft in spots. Tonight as my neighbor was out mowing in the rain, I realized there is on way I am going to keep my yard up to that neighbor's standards.




  • Howard Byer
    8 years ago

    I pulled my craftsman pedal controlled hydro up to a hose at the end of the season. Sprayed off the mower deck and now it won't go forward. It will go in reverse but that's it. Linkage to the pedals looks ok. What did I do?

  • rexlex
    8 years ago

    Byer - most likely your park brake mechanism froze up (corrosion).. best stay away from the garden hose/pressure sprayer scene and use compressed air or leaf blower to clean up instead....

  • bobseader
    8 years ago

    Good afternoon All,

    I had to join & post when I came across this very educational forum, especially when I saw Kerry's L&G mentioned. That's where my 9-season JD LA150 is currently sitting, reportedly with a failed hydro (2nd time in this machine). It ran fine in December, my final cut. I've learned to start this machine occasionally over the winter to ensure it will start in the spring. For whatever reason, I decided to take it for a ride that time, except.... it wouldn't move. I confirmed the rod in the back was pushed in for engagement, then pulled it out so I could move the tractor forward to get a better look underneath. I noticed the drive belt was slack and requested that be addressed/replaced when the shop picked up my tractor for a full P-M. A week later the phone rang- "hydro needs to be replaced". "How do you know?" "Because we jacked it up and the wheels will turn with no resistance"; but I stopped in to visit my machine and when I pushed it, it did seem to have resistance (like always when you try to push the machine without disengaging the trans rod.

    Does anyone know how to diagnose a hydrostatic trans and what the tell-tale signs of failure are? What do you make of the explanation I got (and the fact I can feel resistance when I push it both before & after they picked it up)? Keep in mind the slack in the drive belt. I trust these guys are reputable (about to celebrate 40yrs in business). The facts just aren't adding up for me. Thanks if you can help fill in the blanks for me, appreciate you sharing your knowledge!

  • rexlex
    8 years ago

    when jacked up, the machine's differential will allow the rear wheels to freewheel - albeit one wheel forward while the other in reverse. Suggest you get a second opinion from another shop. hydros usually fail when hot or from control linkage problems. Frozen up park brake mechanisms also often turn out to be a cause.

  • bobseader
    8 years ago

    Thank you very much rexlex!

    I doubt the park brake because I didn't engage it, but good to know. It was definitely not even warm (weather or machine) when this all occurred.

    Also, when I go over there, jack it up, and spin the rear wheel I understand you to say that the wheel on the opposite side of tractor will spin the other direction. Will that indicate the hydro works or that it has failed? Is this test to be done with the trans pin engaged (in) or disengaged (out)? I imagine there should be a fair amount of resistance if all is well, correct? If I determine the hydro may not have failed then I will do exactly as you say and have the other dealer come get it (because I'm probably getting gouged on the other work proposed too). Any other advice? Thanks once again!

  • rexlex
    8 years ago

    bobseader - am only saying that simply jacking up the rear end and then spinning a wheel will not tell you much about the condition/function of the hydro because of the action of the diff. OTOH, the slack drive belt you mentioned earlier is a much more likely clue to the problem.... Yeah, for the $$ involved, would get that 2nd opinion.

  • aethelredtwo
    7 years ago

    I can't believe what I am hearing about the MTD Hydo trans.


    I have a ranch in Montana. I cut a 3 acres every 2 weeks (11 times a year) It has so many hills I have to ride my 42" cut yard machine side saddle most of the time. I have rolled it 3 times in 14 years of use! I am installing a new (pivot bar) (front Axle) now because 14 years of use has reamed out the axle shafts. (this is a pressed metal pivot bar. Not cast iron. That being said. I have way over 800 hours on the engine (B&S 17.5 hp) and the MTD Hydrostatic tranny. NEITHER HAVE GIVEN ME ANY TROUBLE (AT ALL). I have never changed the oil in the tranny (factory says it's a sealed unit) and I believe them.


    I have used 3 MTD tractors on my years in the last 40 years! I have sold all of them for 1/2 of what I paid for them. (I did have one B&S engine throw a rod at 250 hrs. Cost $357 in 1993 to get a new long block and 5 hrs to change the motor.


    My neighbor bought a $4000 JD the same time I bought this mower in 2002. It lasted 3 years and the Kaw. motor blew. He went to JD and they said. That was a really bad motor. We don't replace them and have no other motor to put on your mower. AND we no longer support the trans. on your JD. So he sold it for $600 for parts and was out $3600! (By the way JD said it was really a bad mower they shouldn't have built. But they would be glad to sell him a good one this time. (no discounts mind you!) Ha ha. My little old $1200 (with bags) in 2002 MTD is still running today. So if it runs like a Deere I'd run to the nearest MTD dealer and get a good mower. One with a Hydrostatic trans. that will last I think forever. But I can guarantee you it will last 800 hard hours of use! With no maintenance at all! (Sealed unit) remember.


    I truly think the MTD lawn tractors are the best value for the dollar of anything I have ever purchased in the past 40 years! Other than my MTD weed eater, but that is another story!


    You who are look between that auto CVT and the Hydro. GO WITH THE HYDRO. (SEALED UNIT) You will not be sorry!

    From a 40 year user of MDTS!

  • bobseader
    7 years ago

    rexlex- thanks so much for encouraging me to get the 2nd opinion! I just finished my first cut of the season after I transferred the machine to my selling dealer who fixed what it needed for 1/3 the estimate. The trans needed nothing, not even a belt. Machine ran great, lawn looks great, and I'm sitting down to write a nice letter to other dealer about my refund....

  • rexlex
    7 years ago

    good that it worked out for you. IMHO, that's what this forum is all about. Perhaps you'll be able to help someone else down the line..

  • wheelhorse_of_course
    7 years ago

    Always good to hear good news. Sad to hear about the crook, I hope you get back your money.

  • bobseader
    7 years ago

    Yes, finally received credit. Disappointed (but not too surprised) he didn't call to explain as I requested or apologize. In my letter I asked directly is such "upselling" the standard operating practice?. I suppose no response answers that question. I won't be returning there. The JD has completed three uneventful cuts now. Once again, I really appreciate the insights on this forum, thanks!

  • Ed Dane
    7 years ago

    hi sorry to be so late to the party. I'm currently looking for a new lawn tractor this spring.
    "John Deere warrants their X300 lawn tractor for 4 years or 300 hours and it has a sealed, non-servicable Tuff Torq K46 hydrostatic transmission. If those transmissions were so unreliable think JD would warranty it that long?"

    I can see 2 problems to this statement no offense but #1 a lawn tractor with 300 hrs on it ain't even broke in. #2 I have a old Sears (grey manual trans) That I just purchased another set of mandrels (weak link IMHO) for the mower and it's 29 yrs old. So 4 years also don't impress me much.
    I borrowed my son in laws "monster" JD with the transmission above as it turns out. Well we had done some ditches the yr before and I had covered them with my bob cat but wanted to sift out the rocks & smooth them out. Waiting for my parts on the sears, I figured I'd use the JD right? Hooked up a 4 x 4 harrow rake and the JD only made it around for maybe 20 min, when I felt it needed more power. The more foot throttle I gave it, the slower it went. Well not being my tractor, I unhooked, and drove off to my shop, "to tighten the belt, yuk yuk." This is my first encounter with a hydrostat. I googled the shop manual PDF figured out what everything was and started researching.
    I see here some like swear by hydrostat and some not so much.
    However, after a lot of research anyone on here that believes JD or any other manufacture for that matter, using that the low end hydrostat for any other reasoning but that it's cheap is kidding them self, there are not "just a couple of people" complaining about them, but really quite a few. And a lot of JD dealers facing the same complaint, that they JD & the dealer don't back that transmission. I'm more looking for info on the auto CVT vs the old school belt.
    I'm thinking $24 bucks a year for model specific belts, beats the holy hell out of $2K for that hydro in 5-7yrs.


  • geezer88
    7 years ago

    For what it's worth, I've used CV, gear, and hydro transmission mowers over the years. My use includes many obstacles that need reverse to mow efficiently. The hydro single foot control shines head and shoulders above the other two for this application. Both the gear and CV mowers require fiddling with the gear shift to back up, while with the single pedal hydro, it is just a subtle single foot motion to back the mower away from an obstruction. For my use this is a major feature.

    tom

Sponsored
Through The Garden, Inc.
Average rating: 5 out of 5 stars21 Reviews
#1 Landscape Design Build Firm Serving Virginia/Maryland & DC Area