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[W. Mark Hellinger]

Kind of like running every amp at 2 ohms....

Cooler is cool.

JR
[edit] OK hard to find a straight answer but hydrostatic drives can have problems from too low pressure on the low pressure side (like cavitation that can heat fluid). I've seen multiple recommendations to use the rabbit (fast) throttle setting (don't be a turtle). Mt local repair guy who fixes these puppies made a similar recommendation,,, I don't push it to the max, but fast enough to keep it happy (i hope). Saving gas while possible damaging the hydrostatic drive seems like a false economy. Fast enough, should be fast enough... be the rabbit.   [/edit]

Good points.  For some reason the "dangers of underpowering speakers" comes to mind, but I understand there's a difference or maybe similarities in cavitating amplifiers vs. cavitating hydrostats.

I'll offer I have an early '80's JD 300 garden tractor... it used to be my #1 do everything machine (mow, rototill, push snow and driveway gravel, haul around it's little trailer, haul me back and forth to the post office, place for the birds to roost (on the steering wheel), etc...)  I bought that JD 300 cheap at an auction a couple decades ago with boo-coo hours on it at the time and who knows what it's history was at the time... it was in pretty rough shape when I bought it (looked like it had been rode hard and put away wet for most of it's prior life), but technically "ran" (sort-of).  I freshened it up, and have since put boo-coo more hours on it.  Since getting my X700's (as a solution to our then kitchen window blind incident), the old faithful 300 has been relegated to permanent rototiller duty.  Through it all, that 300 has done a lot of work @ decidedly down from full throttle and a bunch more at WOT... and still pulls like a rented mule... as long as I keep the hydrostat topped off... the steel hydraulic lines on that machine drool like a moose eating apples.

I am aware of hydrostat (?) problems galore with non ground engaging "riding mowers".

[John Roberts {JR}]

Good points.  For some reason the "dangers of underpowering speakers" comes to mind, but I understand there's a difference or maybe similarities in cavitating amplifiers vs. cavitating hydrostats.

not close... damaging speakers by under powering is a well examined audio myth.

I'll offer I have an early '80's JD 300 garden tractor... it used to be my #1 do everything machine (mow, rototill, push snow and driveway gravel, haul around it's little trailer, haul me back and forth to the post office, place for the birds to roost (on the steering wheel), etc...)  I bought that JD 300 cheap at an auction a couple decades ago with boo-coo hours on it at the time and who knows what it's history was at the time... it was in pretty rough shape when I bought it (looked like it had been rode hard and put away wet for most of it's prior life), but technically "ran" (sort-of).  I freshened it up, and have since put boo-coo more hours on it.  Since getting my X700's (as a solution to our then kitchen window blind incident), the old faithful 300 has been relegated to permanent rototiller duty.  Through it all, that 300 has done a lot of work @ decidedly down from full throttle and a bunch more at WOT... and still pulls like a rented mule... as long as I keep the hydrostat topped off... the steel hydraulic lines on that machine drool like a moose eating apples.

beaucoup  (FR for many)

I am aware of hydrostat (?) problems galore with non ground engaging "riding mowers".

I am trying to avoid same by taking advice from trustworthy sources (operate closer to rabbit than turtle).

JR

[Bob Leonard]

The problem with box store "tractors" today is, and always will, be the integrated transaxle / transmission. My 35 year old Craftsman 18hp GT never had a tranny problem, simply because it was 6 speed manual. If you could get traction you could pull a house, and I'll guarantee you I tried. I had some minor issues including an engine rebuild, starter, batteries, fuel pump and starter relay. But never the transmission or axels.

The tranny on the box store mowers are not meant for any type of ground engaging work, or even heavy pulling up hills. Yet, there are 100 attachments that will hook by pin to the back and although some are not ever going to be an issue, box blades and 600lb rollers will be a problem.

Just like speaker heat is the enemy, so what to do? First thing I did was check for tranny type and available accessories/attachments. From all reports Tuff Torq is by far the tranny leader in this department, However, there are many models to choose from, just like speakers.

The entry level trannies used by Husqvarna, Sears, Cub Cadet and others are light duty / intermittent duty transmissions. Never meant for all day work under most conditions, and really not even meant for pushing snow and pulling heavy loads. These are the TT K48, 57, and 58 which almost every box store "tractor" uses regardless of horse power. Cost about $500. A good replacement would be the K66 if you have $1000 to blow.

The worst part about these transmissions is that they really aren't serviceable. Most don't have the option to replace or change a filter, and none of these have an oil reservoir or are designed so the fluid can be changed.

The JD select series like the X580 I bought come at a steep price, and for the almost $10,000 I spent I could have had one hell of a board, new speakers, been drunk for a long time, etc.. The benefit of spending that kind of money is equal to spending better money on audio hardware, and you get what you pay for.

The Select series all have Tuff Torq K72 transmissions. I've read a few bad things, but the approval rating is through the roof, and the K72 is considered one of the best ground engaging trannies available. Removable filter, oil reservoir, and 6 quarts of oil to keep it nice and cool all day long. 1" axel and 430 foot pounds of torque at the axel. Cost for the tranny is $2300.

The final step in the series is the almighty K92 used in the X700 series, rated by far the best of the best with a 1" axel and axel torque rating of 650 foot pounds. The cost is at or about $3600.

You also need to keep in mind that the larger units also supply hydraulics for the front, rear, PTO, brakes and steering. My suggestion is simple. Regardless of where you buy the riding mower, YT, GT, or whatever it's being called take a look at the rear tires. If they're 23" or larger then take a second look if you're interested. Why? Because all of these transmissions are rated for a specific tire size, and just like life, bigger is better.

[Scott Holtzman]

While you guys are talking about operating RPM it got me to thinking.  I was told to always run my Bush Hog Zero Turn at full power as the rear wheels drive off of hydraulic power packs.  SV820 23HP Kohler engine has been bulletproof. 

[Bob Leonard]

That would be a myth Scott. ZT mowers rely on a pair of units, one for each wheel. These units are designed to have a maximum rpm, not a minimum rpm. The maximum rpm for the hydro tranny is determined by motor rpm and the size of the drive pulley. Running at top rpm only creates more heat, pushing the hydro drive to its limits.

Also, the oil should be changed at 50hrs and at every 200 hours after that.

A quick check shows Bush Hog uses Hydro Gear units. Depending on the model you own it won't have anything smaller than the unit at the link below. The operating range is 1800 rpm to 3600 max rpm. MAX 3600.

http://www.hydro-gear.com/zt3100/

[John Roberts {JR}]

That would be a myth Scott. ZT mowers rely on a pair of units, one for each wheel. These units are designed to have a maximum rpm, not a minimum rpm. The maximum rpm for the hydro tranny is determined by motor rpm and the size of the drive pulley. Running at top rpm only creates more heat, pushing the hydro drive to its limits.

Also, the oil should be changed at 50hrs and at every 200 hours after that.

A quick check shows Bush Hog uses Hydro Gear units. Depending on the model you own it won't have anything smaller than the unit at the link below. The operating range is 1800 rpm to 3600 max rpm. MAX 3600.

http://www.hydro-gear.com/zt3100/

1800-3600 rpm sounds like a minimum speed recommendation to me (not below 50% max).

While I haven't found a definitive published explanation, cavitation in the low pressure side from too low RPM sounds plausible. While my explanation may be myth, the advice to not run them loaded at too low throttle seems pretty universal, including from people I trust (people who repair them).

Of course this is an audio forum so caveat lector.

JR

[TJ (Tom) Cornish]

1800-3600 rpm sounds like a minimum speed recommendation to me (not below 50% max).

While I haven't found a definitive published explanation, cavitation in the low pressure side from too low RPM sounds plausible. While my explanation may be myth, the advice to not run them loaded at too low throttle seems pretty universal, including from people I trust (people who repair them).

Of course this is an audio forum so caveat lector.

JR

I would agree with this.  I have a JD 4110 compact utility tractor (21HP diesel, fully hydraulic) and I get very little useful work done at less than 1/2 rated speed (on my tractor that's more like 1200-2400 RPM, but same principle). 

[Steve Crump]

I would agree with this.  I have a JD 4110 compact utility tractor (21HP diesel, fully hydraulic) and I get very little useful work done at less than 1/2 rated speed (on my tractor that's more like 1200-2400 RPM, but same principle).

+1.
I have a Kubota B2910 and a Kubota TG1860, both diesels and get the same results as Tom.

[Bob Leonard]

I have to agree to all the above. I also feel half throttle about all you ever need, and on my machine that's a bit less than 2000 rpm. My point above was that there is no reason to constantly run equipment at full throttle. It's hard on the equipment.

[Scott Holtzman]

I have to agree to all the above. I also feel half throttle about all you ever need, and on my machine that's a bit less than 2000 rpm. My point above was that there is no reason to constantly run equipment at full throttle. It's hard on the equipment.

My blades are belt driven so now I want to let some grass grow to see if 2000 RPM is enough blade velocity to tackle the tough stuff.

I need to find a torque curve for the engine.  I would imagine for the blades peak torque is more important than RPM.