" Not necessarily specific to a make or model just generally whether it be a new big box mower or an old iron tractor."

I have the older Ford LGTs, 3 hydros and a gear....As for durability, I would put them about equal.

Also have a JD STX38 hydro for cutting grass. I would not even compare that hydro to the Fords. You can tell just driving up a hill etc that it is not nearly as strong.

 

Yes the type and model of hydro has much to do about reliability. Garden Tractor hydro's normally are a lot stronger than Lawn Tractor and Lawn machines as they are "ground engaging" which requires the machine to be able to handle the low end torque needed.

 

Those old(er) Sunstrand hydros are just as reliable and strong as any manual trans of that era and especially better built than any hydro or manual of today using same comparison of size tractor.

Just compare the transaxles between old and new. Iron cases compared with aluminum. Lighter doesn't make it better for strength.

I also have an old IHCC 102 w/manual from 1967 and a newer 2003 Craftsman GT5000 w/manual. While the GT5K with its 24hp engine is good and is a well built tractor, it'll never compare to that old 102 with its 10hp motor and how well built it is and what it can do with implements.

I also have a 1990 industrial/commercial mower using an ONAN engine and it also uses a Sunstrand pump system just like the old IHCC mowers used, and it has no problem pushing a 1200# mower around with ease. The transaxle system the pump attaches to is a Toro Groundsmaster(still searching as to what model # it is), which is just as equal as a IHCC transaxle. Both are iron cases.

Del

 

LT/GT transmissions are rated for their torque handling capability. Not so much for the input torque, but for what they can deliver to the rear axle. The big difference is in how that torque is generated.

Manual transmissions transmit the engine torque directly via gear reduction and it's a straight multiplication exercise to calculate the axle torque.

A hydro supplies torque to the rear axle all out of proportion to the engine's capability. Small hydros (LTs) can only transmit a portion of the engine's torque. At the other end of the scale, the big hydros (GTs) send more torque to the axle at lower engine speeds than what they can send at the maximum speed. A hydro's torque is independent of engine torque production, but it factors in the engine's horsepower production. Its torque is calculated using the displacement per revolution of the hydro motor and the pressure required to turn the hydro motor and is subject more to the engine's horsepower than its torque.

Basically the manual transmission is used to transmit horsepower, and the hydro is used to transmit torque. There is a distinction between them. Torque gets the load moving, horsepower keeps the load in motion once it is moving, and the larger hydros can deliver a LOT of torque.

LTs have huge engines in relation to the power handling capability of the hydro. GTs have been made with engines that are not large enough to produce the power that their hydros are capable of delivering. A specific example is the JD 112 with a Sundstrand Series 15 hydro that can eat 14 hp at 1500 psi but only has a 12 hp engine. In that application, the hydro is, for all intents and purposes, indestructible. Since that hydro is rated for 2500 psi continuous, any engine up to 24 hp is a 1:1 for hydro durability.

Small hydros tend to be overused with the result that they overheat and don't last as long as an equivalent manual transmission. No manufacturer has installed a manual transmission in a modern GT with more than 20 hp to my knowledge. There are a couple of old school GTs with more than 20 hp and a manual transmission, but they used car transmissions.

As with trucks, there is no easy comparison. Each has its own strength and the end use is where the comparison must be made. If you try to deliver more power to the axle than the transmission can handle, both types will fail.

 

I’m presuming what @Outdoorsben is really trying to posit: Generally speaking with all things being equal, is a manual transmission is stronger than a hydrostatic transmission?

Obviously a LT hydro won’t be as strong as a HDGT, but the theory here is LT vs LT, GT vs GT, CUT vs CUT, etc....

While we could easily get lost in specifics like brands, generations, classes, etc, the KISS method is probably best for this one.

 

We have a problem. Define "stronger".

Basically the manual transmission is used to transmit horsepower, and the hydro is used to transmit torque. There is a distinction between them. Torque gets the load moving, horsepower keeps the load in motion once it is moving, and the larger hydros can deliver a LOT of torque.

A visitor next door saw my little MF12H/FEL parked in front of my 18' travel trailer (3600 lb) and stated "You're not going to pull that trailer with that little tractor!", or words to that effect. (My memory is just a bit fuzzy on the exact wording. It was about 35 years ago.)

Challenge accepted!

Engine at idle, hooked up the trailer to the ball on the GT, bashed the drive control full forward (hand control), then immediately did the same for the throttle. The engine stumbled momentarily as it took a full gulp of air under max load before the fuel mix could stabilize. Once the governor got its act together for the rapid change of power demand, it then settled down to accelerate the load to about 8 mph in about 20'.

Try that with a MF12G with the manual transmission, and the engine will stall when the clutch is dumped if it's in a gear high enough for a travel speed of 8 mph, or if it's in a gear low enough for the engine not to stall, it will only make 2 or, maybe, 3 mph.

That's the torque side of the equation. On the horsepower side, with the same load once moving on a long grade, the manual transmission will get to the top of the hill sooner, or won't work as hard getting there, because there is some loss of horsepower with the hydro due to normal internal leakage of hydraulic fluid under pressure. The engine has to pump that fluid whether it is doing actual work or just leaking normally, and that leakage uses about 20% of the horsepower applied to the transmission.

There's more to it, but we will assume that the slope is such that the manual transmission can handle the load and slope in high gear at WOT.

Note that the only tasks that will demand maximum sustained performance from a transmission are ground engagement (ploughing, discing etc,) or slope climbing. The majority of tasks will only require a relatively small percentage of the maximum performance with, possibly, a few moments of max performance thrown in for good measure.

The MF12G and H are well suited to a direct comparison of transmission performance characteristics. They both use the same final drive (reduction gears and differential), the G with a set of manual gears in front of it, and the H with a hydro, and both have an HH120045B Tecumseh 12 hp engine.

I also subscribe to the KISS theory, but sometimes it simply can't be applied because of varying conditions. In this case, the type of work determines which is stronger.

Note that the OP's original question referred to a comparison of the durability (strength of shafts, rotating parts, and case) of the two types of transmission, not to the performance. The answer to that was given earlier . . . they're about equal when used for the tasks for which they were intended and designed.

 

My 1968 Sears Suburban Super 12 has a manual 4 speed with 2 ranges, and the only thing I was able to break on it was a weathered old belt. All day long project pulling shrubs out with chains and doing many "wheelies" did that old drive belt in. I couldn't catch an earthworm in low range and first gear.

Now retired, but otherwise still strong in all gears. I sort of miss the old clutch pedal too.