425 again…movement problems…

[ponytug]

Not trying to start a war but what makes a power trac hydrostatic drive any different than a skid steer or any other hydrostatic driven vehicle?

No worries.

I think that the design, and to lesser extent operational differences make Power-Tracs quite different from skidsteers and most other hydrostatic drive equipment. Power-Trac machines are wonderfully simple, solid machines that lend themselves easily to shade tree repairs. However, that means that they don't have the bells and whistles that you would find on a John Deere or Bobcat. In particular, the 425 that @Modrob is dealing with has a gasoline powered engine (similar to your x540) that usually runs at a fairly high throttle, ideally wide open due to air cooling issues intrinsic to the particular engine. That means that the pumps are running at full speed, when they are most prone to cavitate.

Bobcat, CAT, Kubota and others are generally diesels that in normal operation are running at low throttle most of the day. Many have mechanisms on their machines, or at least the ones that I am familiar with, that help get the hydraulic oil to temperature quickly, and many suggest in their owners manuals that the machine not be operated or moved in cold temperatures until the machine and its oil are up to temperature. That is also why many of those machines are designed for, and use, straight 30W hydraulic oil, as the manufacturer expects the machine only to be used when the oil is at temperature.

I'm not saying design version X is better, or worse, than Y, just that there are some significant differences between Power-Tracs and more common machines, and that experiences with other machines may or may not carry over to Power-Tracs. E.g. The only interlock on a Power-Trac are the starter key, and a PTO lockout during starting.

Over the years, I have operated a wide range of tractors, and I will say that for the purposes of our current property that has significant slopes, "There's nothing like a Power-Trac". Horses for courses. These are not your typical tractors, and that's why generic advice can be off base, but there are reasons why Power-Trac owners tend to be fans.

On the other hand, I would never attempt to pull a plow with a Power-Trac; low speed, high torque, ground traction isn't their design, nor is it going to haul a grain cart or a baler well.

Being a Swiss Army knife type machine that is excellent on slopes is what Power-Tracs excel at. A neighbor down the road was killed when he tried to operate a standard tractor on slopes.

All the best,

Peter

 

[m5040]

Not trying to start a war but what makes a power trac hydrostatic drive any different than a skid steer or any other hydrostatic driven vehicle?

Spin on suction filter for one, which is not a typical arrangement and requires adherence to the oil specs and service interval of 50 hours for a filter change.

 

[oldnslo]

Spin on suction filter for one, which is not a typical arrangement and requires adherence to the oil specs and service interval of 50 hours for

The suction filter is not that unusual since both the BX1850 I had and 2400H I have now had them.

The 50 hour filter change does seem unusual though

 

[m5040]

The suction filter is not that unusual since both the BX1850 I had and 2400H I have now had them.

The 50 hour filter change does seem unusual though

I am just trying to learn here. Why do you think the BX1850 trans filter is on the suction side? The parts diagram shows one filter integral with the transaxle and without a internal flow diagram, it most likely is filtering returning oil (it is easy to push unlimitedly through filter media, but vacuum to pull oil is limited to atmospheric pressure).

The 50hr filter change is due to PT using it on the suction side. I don't like this setup, but it works. I have seen neglected Power Tracs for sale that, at least appear, to not have had the hyd filter changed in years and yet the drive still works.

 

[oldnslo]

The reason the filter is on suction side on utility is that the return oil is typically from 3 point hitch valve which dumps straight into the transaxle. On my 2400H their is a suction filter for both implement and charge pump and also a spin-on filter for the pressure inlet of the charge going into the HST.

The suction filter or screen is there to remove contaminants generated by the turning gears in transaxle, particles from PTO clutch, wet brakes, etc.

I agree that suction filter is not ideal but sized properly they do work.

If 50 hour change is required I would suspect a design problem with either a component generating a lot of debris or a very undersized filter since as filters remove contaminants the pressure drop across them increases.

 

[ponytug]

The reason the filter is on suction side on utility is that the return oil is typically from 3 point hitch valve which dumps straight into the transaxle. On my 2400H their is a suction filter for both implement and charge pump and also a spin-on filter for the pressure inlet of the charge going into the HST.

The suction filter or screen is there to remove contaminants generated by the turning gears in transaxle, particles from PTO clutch, wet brakes, etc.

I agree that suction filter is not ideal but sized properly they do work.

If 50 hour change is required I would suspect a design problem with either a component generating a lot of debris or a very undersized filter since as filters remove contaminants the pressure drop across them increases.

The filter is a little on the coarse side (30 microns), but many machines have even coarser filters. My recollection is that the logic on the filter choice and size is that unlike other machines with 30W oil and warmer oil, the filter on Power-Tracs has to deal with cold oil without collapsing. The filter feeds the charge pump for the variable volume pump, so the flow starts on engine startup, again, not always the case on other hydrostatic machines. A filter collapse would probably be terminal to the main pump, hence the low hour filter change requirement.

Could things have been done differently? Without question. One could treat the hydraulic tank as "clean" and filter 100% of the return fluids, and many of the larger machines do exactly that. PT chose not to do that in the pursuit of lower engine loads. It was a design choice, and it seems to work.

As I wrote, PTs are a little different...

All the best,

Peter

 

[oldnslo]

Peter,
I don’t know of a hydrostatic system where charge pump does not turn when engine starts. All hydrostatic systems require a charge pressure to operate without self destructing. On some designs the charge pressure is used to stroke the pump so without charge pressure the machine will not move. I believe but not positive that PT uses a direct mechanical control to the hydrostatic pump so it will move without charge pressure IF the closed loop portion of system is full of oil. With charge flow system leakage empties this circuit and cavitation begins.

 

[m5040]

I don’t know of a hydrostatic system where charge pump does not turn when engine starts.

I have a Kubota powered Hustler Excell that starts without the charge pump or any other spinning.
The later model Power tracs have pilot control for the drive system.

 

[ponytug]

Peter,
I don’t know of a hydrostatic system where charge pump does not turn when engine starts. All hydrostatic systems require a charge pressure to operate without self destructing. On some designs the charge pressure is used to stroke the pump so without charge pressure the machine will not move. I believe but not positive that PT uses a direct mechanical control to the hydrostatic pump so it will move without charge pressure IF the closed loop portion of system is full of oil. With charge flow system leakage empties this circuit and cavitation begins.

Some models have mechanical control of the stroke. Mine doesn't.

Not all brands of hydrostatic drive machines support cold movement, per their manual, although it might be possible for some, I don't know.

To me the distinction is whether the system is designed with a warm, clean oil reservoir in mind, or not. If not, then the filter has to be able to deal with high viscosity oil without failure. I did the math a while back, and it turns out to be a rather big ask to limit the pressure drop to be within the filter's rating at low temperatures. I was surprised. One fix could be that one could use a high pressure rated filter suction filter ($$$), but while that helps not to have a catastrophic filter failure, it could (would probably) introduce degassing due to the large pressure difference across the filter, and air bubbles are really hard on pumps. So, I don't necessarily think that is a win, but might work if one was just warming a machine up.

I think it all comes back to design. Power-Trac seems to have designed for cold oil intake of not necessarily clean oil, putting a large filter (low pressure differential with cold oil), but needing to be changed frequently to maintain the low pressure differential.

All the best,

Peter

 

[Modrob]

Not a lot to be done about cavitation; slow the engine speed down, especially when cold, don't work it had while cold, and possibly change the hydraulic oil to fresh 10W40. How does the hydraulic oil look? Do you know when it was last changed, and what oil was used?

If the pump is worn it may be more prone to cavitation and there isn't much to be done about that.

All the best,

Peter

Hey Pete…back in town again and had a chance to look back at the oil I put in—it was 5w30, and that was what I was advised to put in at that time. (And new filter)