HST or shuttle shift gear transmission?

60463 Views 14 Replies 13 Participants Last post by Wyobuckaroo, Jan 1, 2012

tc25dnewholland

Discussion Starter · Dec 11, 2011

I would like to hear your opinions on why HST is better than shuttle shift gear transmission. All the dealers I have contacted tell me HST is best for general use and 90% of compact tractors are sold with HST. I have not seen a lot of HST in large tractors, so why is it so much better in a compact tractor? I don't like the way an HST tractor has to have the RPM's ramped up to 2,000 just to drive it! Also the hp. loss at PTO is substantial. Well please convince me why HST is so wonderful and the only way to go!

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Volfandt

· #2 · Dec 11, 2011

Welcome aboard tc25dnewholland.
As it is with just about everything, theres no single "best" at everything tranny for a tractor.
Alot depends on what your intended uses will be.

I think an HST is better suited for SCUTs & CUTs due to their primary usage being finish mowing. I have mowed w/an HST & gear tractor and I much prefer the HST for mowing.

A shuttle shift can't match the instant & effortless speed changes of an HST but it can match the directional changes which makes it just about equal w/an HST in FEL work.
Your arguments in the characteristics of the HST are spot on, you do have to ramp up the rpm and there is a loss of hp at the pto, when compared to a similarly sized gear or SS tranny.
i believe all the manufacturers make a gear tranny CUT model, I know JD, Kubota & MF does. Theres not a thing wrong w/prefering a gear/SS tranny over an HST. If thats what you want thats what you should get.
You are the one thats got to own & operate it

Dave

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NEWT92

· #3 · Dec 11, 2011

:Welcome1: tc25dnewholland.

Ill agree, it all depends on your use for the tractor. If your gonna do loader work/mowing, HST is the way to go. If your gonna do a lot of heavy pulling on the transmission (plowing, disking, etc.) then gear drive would be better IMO.

Also, resale value will me much better on a HST equipped tractor. :fing32:

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username

· #4 · Dec 11, 2011

NEWT92 said:
:Welcome1: tc25dnewholland.

Ill agree, it all depends on your use for the tractor. If your gonna do loader work/mowing, HST is the way to go. If your gonna do a lot of heavy pulling on the transmission (plowing, disking, etc.) then gear drive would be better IMO.

Also, resale value will me much better on a HST equipped tractor. :fing32:

+1 and I would like to add snow blowing to the list.

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Nouveau Redneck

· #5 · Dec 12, 2011

I don't like the way an HST tractor has to have the RPM's ramped up to 2,000 just to drive it!

My only comment on that is that diesel engines, which are what drive most CUTs and SCUTs these days, do not like to be run at low rpms for extended periods. They are designed to be run at or near their optimum output rpm, which is usually somewhere between 2000 and 2800 rpms.

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Larry from MT

· #6 · Dec 12, 2011

When I bought my Case D40 I was told (by the dealer) that the Shuttle was recommended for front end loader work and also for cold weather operation over the Hydro.

TUDOR

· #7 · Dec 12, 2011

Newt92 nailed it! HST for precision speed control and SST manual transmissions for bullwork.

What tasks you expect to use the tractor for will determine the best transmission for you. The lower PTO horsepower from a hydro can be compensated for by slightly lower travel rates, and the small amount of time lost can be recovered by speeding up when the load is lessened. eg. Slow down when blowing through a big snow drift and speeding up for the areas with little snow.

I'm curious as to why there is a different PTO horsepower rating for the 2 transmissions. Most PTOs are direct coupled to the engine, not the transmission. Transmission power loss for hydros is commensurate with the amount of work that the hydro is doing, and that is not much when a PTO powered implement is being used. I cannot think of a situation where the tractor is moving at top speed under heavy load and traction when using a powered implement, and that is where the lowered PTO rating will be generated.

Now if your normal mode of, say, snowblowing involves towing a 2 ton sander up a steep hill at the same time as you are blowing through 2' drifts at 5 mph, then yes, the higher PTO rating of a SST might be beneficial. But at anything less than full speed, the hydro inefficiencies will be lessened accordingly and more power will be available for the PTO.

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kgrover

· #8 · Dec 13, 2011

I'm not sure exactly how the hystat transmissions are designed on CUTs but I'm very familiar with them on construction equipment. With a closed loop hystat system you need a charge pump that is constantly pumping oil back into the loop. This is most likely what accounts for the drop in power at the PTO.

Rated engine power - charge pump draw - (Other loads like steering, alternator, ETC) = Available PTO power.

With a gear transmission there is no charge pump.

The charge pump is there to cover the internal leakage of the pump and motor. In a closed loop system the pump pushed oil to the motor, the oil turns the motor, and returns back to the inlet side of the pump. This is so that when you want to go in reverse, the pumps displacement just swings the other way and sends oil down what was the return line. There is internal leakage in between the pistons and their housings and other rotating seals. The charge pump provides the make up flow for this leakage and keeps the low pressure side, or return side, of the loop at a minimum pressure so that the pistons always have something keeping them seated on the plates.

Charge pumps pressure is usually around 3000 kPa, or 430 PSI, the loop pressure in the hystat typically peaks somewhere above 40,000 kPa, or 6,000 psi.

The charge pump displacement is usually pretty small as well but depends on what the system leakage is and what other things might be using the supply from the charge pump.

It's not a huge power draw, but I think this is what accounts for the difference.

The main question you need to ask is do you need all that PTO power all the time? Is the tractor going to be running a pump or genset and see that constant, full horse power load, or is it going to be running a brush hog or mower or blower and only need the peak power occasionally where having a few less HP is worth the control ability of the hystat?

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schmart

· #9 · Dec 13, 2011

I agree that Newt on HST if you have a loader on the tractor. Although you MAY be able to get slightly more digging force with a shuttle transmission, you won't be able to use the loader to creep into position as easily or as accurately if using the loader as a crane. I for instance frequently use the loader to lift a heavy object and set it on the tailgate of my pickup. There is no way I would try that with a shuttle transmission. It would be way too easy to take out the side of the bed!

Landscaping is another area where the Hystat is useful. I was able to creep right up to the side of my building with fill dirt using the hystat. Again with a manual transmission, I would have had to stop back 18" or so to feel comfortable that I wasn't going to drive through the side of the building.

--Rick

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Loremaster72

· #10 · Dec 14, 2011

Interesting discussion. One point to add to the hystat description by Kgrover. Charge pumps are also frequently used to provide loop flushing on the system. This is an intentional "leak" in the system that drains a planned amount of oil at the pumps and/or motors. This serves the dual function of helping to keep things cool and move any contaminants out of the components and back through the filtration system. The charge pump provides this, in addition to the makeup oil needed for true leakage.

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walterboatwright

· #11 · Dec 14, 2011

I dont know about bullwork with a hystat.Grading with a box blade can sometime be hard to pull as a plow.And the hydra-stat transmission in farm tractor has been around since the sixties.It is really come of age the last few years. But I have never understand why there is no cooling coils.But there are chances as long as its not yanked around it could pull a plow in a garden or other pulling work.

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tc25dnewholland

Discussion Starter · #12 · Jan 1, 2012

kgrover said:
I'm not sure exactly how the hystat transmissions are designed on CUTs but I'm very familiar with them on construction equipment. With a closed loop hystat system you need a charge pump that is constantly pumping oil back into the loop. This is most likely what accounts for the drop in power at the PTO.

Rated engine power - charge pump draw - (Other loads like steering, alternator, ETC) = Available PTO power.

With a gear transmission there is no charge pump.

The charge pump is there to cover the internal leakage of the pump and motor. In a closed loop system the pump pushed oil to the motor, the oil turns the motor, and returns back to the inlet side of the pump. This is so that when you want to go in reverse, the pumps displacement just swings the other way and sends oil down what was the return line. There is internal leakage in between the pistons and their housings and other rotating seals. The charge pump provides the make up flow for this leakage and keeps the low pressure side, or return side, of the loop at a minimum pressure so that the pistons always have something keeping them seated on the plates.

Charge pumps pressure is usually around 3000 kPa, or 430 PSI, the loop pressure in the hystat typically peaks somewhere above 40,000 kPa, or 6,000 psi.

The charge pump displacement is usually pretty small as well but depends on what the system leakage is and what other things might be using the supply from the charge pump.

It's not a huge power draw, but I think this is what accounts for the difference.

The main question you need to ask is do you need all that PTO power all the time? Is the tractor going to be running a pump or genset and see that constant, full horse power load, or is it going to be running a brush hog or mower or blower and only need the peak power occasionally where having a few less HP is worth the control ability of the hystat?

Hi kgrover, Good understandable description on HST:thanku: I'm not the most coordinated person so the HST may be best for me:dunno:. I have seen quite a few tractors for sale with 200 to 300 hrs. and have already had there clutches replaced. A single stage clutch is not inexpensive but the 2 stage clutches are definitely costly. Well I think I'm glad I didn't get in a hurry on my new tractor purchase. Came very close to buying a new LS G3033 (gear)from Lane Tractor in Los Molinas Ca. a couple of days ago. The LS H3033(HST) is looking better all the time.

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tc25dnewholland

Discussion Starter · #13 · Jan 1, 2012

Volfandt said:
Welcome aboard tc25dnewholland.
As it is with just about everything, theres no single "best" at everything tranny for a tractor.
Alot depends on what your intended uses will be.

I think an HST is better suited for SCUTs & CUTs due to their primary usage being finish mowing. I have mowed w/an HST & gear tractor and I much prefer the HST for mowing.

A shuttle shift can't match the instant & effortless speed changes of an HST but it can match the directional changes which makes it just about equal w/an HST in FEL work.
Your arguments in the characteristics of the HST are spot on, you do have to ramp up the rpm and there is a loss of hp at the pto, when compared to a similarly sized gear or SS tranny.
i believe all the manufacturers make a gear tranny CUT model, I know JD, Kubota & MF does. Theres not a thing wrong w/prefering a gear/SS tranny over an HST. If thats what you want thats what you should get.
You are the one thats got to own & operate it
Dave

Hi Dave, Mostly mowing,box scraping, and general loader work. Maybe a disc or rototiller later on. All of the dealers I have talked to recommend the HST. Considering my lack of tractor operating experience and advanced age,the HST may be a logical choice. Resale is also a consideration.

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c5rulz

· #14 · Jan 1, 2012

My last GT, (Honda 5518, 4WD, 4WS) had an 8 forward speed and 4 in reverse. After having a HST, you will never go back for tasks as mowing and loader work. Actually I can't think of a task other than maybe pulling a plow in a straight line where a gear drive would be preferable.:greendr:

Wyobuckaroo

· #15 · Jan 1, 2012

After a little over 1 1/2 years of having both a lawn tractor and a compact with HST, I would throw away a gear tractor for the work that these have done.

My two cents worth is that utility and smaller row crop tractors are a good fit with gear drives. This theory has worked well with my needs.

Your millage may vary
Good luck

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