Nasty Little Hydrostatic Transmission Secrets...

jinman · Mar 1, 2004

( This only happens in relief conditions. )

This is exactly my point in my first post when I said that if the TC35D pops the relief valve, the TC40D or TC45D can do no better. Or said another way(taking my example to a ridiculous level), it does not matter whether you have a 12-yr old boy or an 18-wheeler pulling on a 6-pound test fishing line. When you exceed the line's rating, it's gonna break. Because the 18-wheeler has more torque, hp, weight and traction, he can't land a bigger fish than the 12-yr old boy. That's the situation I'm describing with the TC35D and its big brothers. If the TC35D pops the relief valve, the bigger guys can do no better. 

Now I'm not saying for a second that in non-relief conditions the other tractors cannot pull more. They have more weight for traction and higher torque for pulling. We have to set up a situation where the TC35D opens its relief valve or this is completely a moot point.

I think New Holland owners will back me up when I infer that our tractors open their relief valves before we expect them to. I can hope that Kubotas, John Deeres, Kiotis, and any other hydrostatic transmission will not have the "New Holland Anomaly" as I've come to accept on my tractor. You truly have to experience this phenomena to appreciate it. /forums/images/graemlins/crazy.gif

I love my hydrostatic transmission, but it has some faults. I realized many of these when I bought it. I'm just now understanding why the "problem" exists. Too bad the Nebraska tests don't include the NH Boomers. I'm sure their data could shed some light on my hypothesis. /forums/images/graemlins/cool.gif

jinman · Mar 1, 2004

JayC, I'm assuming you are not talking about the TC48DA or TC55DA since neither of those tractors are hydrostatic transmissions. On the TC35-45DAs, I think they all have the same transmissions as our current tractors. If so, they will act the same way.

I don't want to worry you. The extra hydraulic pressure for the FEL and 3PT are significant. If you want all the power your engine has to offer, you still need to buy a gear tractor. /forums/images/graemlins/blush.gif

Now all you fellow hydro owners please do not stone me. /forums/images/graemlins/shocked.gif /forums/images/graemlins/laugh.gif

rambler · Mar 1, 2004

All hydraulic systems have fairly severe limitations. Farmers understand this, and only a very few real tractors with hydro have been popular for limited applications. Some IHC hydro tractors for loader work, baler, trenching, feed cart, and other variable speed, lower pulling hp application; and now a days mostly skid-steer (Bobcat) type loaders are all hydro.

The only other place hydro drive is popular are compact tractors, where the buyers are paying a premium for a tranny that is more convienent, but delivers far less hp from the engine to the ground. This was all 'discovered' back in the '50s by farm types, so is all really old ground. Doesn't matter what color the tractor is, there is great power loss & innefficiency in transmitting power by oil lines, exponentially with increased power loads.

I'm not knocking hydro drives or anyone's particular tractor. You all just need to realize you are paying premium $$$ for a convienence that steals power, performance, & hp from you. A dealer is going to push a hydro on non-farmers, bacause you don't know and you have the bucks to spend on the bigger mark-up and the dealer makes more on $$$ options.

Just how it is. Don't blame any dealers for this - standard business.

Me, I would not have any use for a hydro _tractor_. Skid-steer yes, lawn mower maybe. Tractor - no. If you only mow lawn, hydro tranny is fine. If you plan to plow or pull max loads - no hydro.

I believe the hydro tractors are built to pull a rotory mower or tiller, so much of the hp goes out the rear pto, and it is designed for only some power to the rear wheels in less than max pull. Just like a skid-steer is built to lift heavy loads, not for pulling.

If you want a pulling machine, get a real clutch tranny. ONLY way to go or you will be deep in repairs & wasted fuel.

Don't mean to be harsh or start anything, just trying to be brief. /forums/images/graemlins/smile.gif

--->Paul

jinman · Mar 1, 2004

( I'm a little confused and a bit suspicious about this theory. )

Bravo! Don't ever take what I say at face value. Make me prove it. /forums/images/graemlins/grin.gif

( On water pumps, lets say you pick a pump rated for 250 GPM at 50 psi...and the resulting required horsepower based on the pump design is 10 HP. Plug in the pump and you'll get 250 GPM at 50 psi.

Now if you substitute a 7.5 HP motor, the pump will still move water, but it will peak at a lower flow and pressure. The result is that the pump will deliver less work ( power ) with the lower HP.
)

Okay, here's my theory applied to your pump with two input HP motors. Let's say you had a pressure relief valve set so the 7.5 hp pump could cause it to open. Would adding a 10 hp pump get you anymore flow? I don't think so. The only place the increased flow would go is out the relief valve. In our case on our tractors, that's back to the fluid reservoir. Doesn't that make sense? /forums/images/graemlins/confused.gif

At least you know that I'm not biased toward my own tractor. /forums/images/graemlins/shocked.gif /forums/images/graemlins/laugh.gif /forums/images/graemlins/laugh.gif

KrisHansen · Mar 1, 2004

These limitations apply to all HST CUTs AFAICT.. My parent's old Orange B24 was bad enough that I had originally been shopping for a manual transmission tractor, till I started thinking about ease of use, and the NH salesman assured me that the TC33D was heads and shoulders better than the B24 (it is)..

I have not managed to stall or pop the relief (as far as I can tell..) valve in low, I just get lots of wheelspin.

RickB · Mar 1, 2004

I am not prepared to defend this one way or the other, but without proving the range gearing, ring and pinion ratio, bull gear ratios and tire sizes are the same, it is incorrect to state the maximum tractive effort in a given class of tractors is limited solely by the relief valving in the hydro. I do not have info at home to verify the components installed behind the hydro. They may well be common among these tractors. They also could easily have different ring and pinion ratios and governed speeds. In addition, IH's large frame hydrostatic tractors from the 70's and 80's produced far more drawbar HP than a Class III New Holland at similar relief settings, but that is another discussion.

LAGEORGE · Mar 1, 2004

Jim, I want to make something clear about the relief valve on the two TC 24D’s I owned. I never popped the relief valve going forward. The tractor would stall out at any throttle setting or HST range if the going got too tough. On the other hand the relief valve would often open when going in reverse with a big load. This I was told by New Holland was done for safety and is not a design problem with the HST . I agree it is a real drag and if I would have known better prior to my purchase I may have looked elsewhere or even considered a gear type. It does not make sense that buying extra horsepower does not get you more power to the wheels. I can tell you that does not apply to the TC 24D. You get power all the way down to a stall!, going forward that is.

George

SacandagaBrad · Mar 1, 2004

( Brad, when I first heard of this problem, I thought about your having a full FEL bucket while trying to back up the slope.)

Jim,

Wrong guy, same tractor. I believe that was LA George with the bucket full backing up the slope. My situation was having the tractor buried in heavy mud on the flat, with the front buried down a little deeper, and the wheels would not spin to back me out. The other situation that really got me wondering about all this was trying to cut down an icy pile of snow, easing into it with the bucket to cut through, and having the wheels lock up as I try to slowly move forward while raising the bucket to break some chunks of ice loose.

The Class I machines only have the Hi/Lo range, no mid range. The tractor has a lot of power and I feel a little silly complaining about all this, but I sure have learned a lot /forums/images/graemlins/blush.gif. Under most circumstances, it will spin 3 wheels with the diffy lock engaged, it is just those few times that got me wondering.

I work on a small piece of property, do some loader work, move docks, launch boats, move trailers, grade roads, blow and plow snow, and will probably use it for most of my mowing. I still think the hydro is the way to go for me. For the uses I stated above, the ability to switch direction easily and also move at a snail's pace when needed is a big plus.

Brad

OkeeDon · Mar 1, 2004

( You all just need to realize you are paying premium $$$ for a convenience that steals power, performance, & hp from you. A dealer is going to push a hydro on non-farmers, because you don't know and you have the bucks to spend on the bigger mark-up and the dealer makes more on $$$ options.)

Um, that's kinda putting all the fish in one barrel, isn't it? I knew exactly what I was getting, and I know the difference between direct gear couplings and a fluid coupling. My dealer didn't push anything -- just the opposite. I think the markup percentage on the hydro tractor is the same as the gear tractor -- that's part of the basic package for that model, not really an option. The hydro isn't stealing anything from me -- I voluntarily gave it up in order to get much better control. And, I didn't really have the bucks -- I started off looking at used tractors, and had to finance this one.

I can't pull what a big, agricultural gear tractor can pull, but then, I don't need to. I'm not plowing anything. I've pulled a heck of a lot more than just a mower, though, like a fully loaded dump trailer, and I only have an 18 HP hydro. I've put 350 hours on it and haven't "mowed" yet, unless you count some fairly heavy duty brush hogging, a fraction of my use. It's been all loader and box blade use, and it's perfect for that -- I wouldn't like to shift gears or use a clutch for that kind of work.

SacandagaBrad · Mar 1, 2004

( You get power all the way down to a stall!, going forward that is. )

George,

Can you do that with light pedal pressure, effectively in a "lower" gear while in low range? Or are you talking about pushing the pedal all the way down in low range? I can stall mine doing the latter. With light pressure where the wheels should be just churning away like being in the lowest gear on a gear machine, sometimes the relief valve pops depending on how much traction I have. At that point, if I push the pedal down further, it will eventually stall.

Brad