More torque for my Power trac?

[KentT]

The behaviour is the same as mine, although the plumbing is a little different. For some reason, PT has added a L/R equalizer hose on mine. But, yes, if you lock two wheels and raise two off the ground, turning one causes and an equal and opposite movement in the other wheel off the ground.

I guess you could get 4 solenoids and electronically "brake" wheels as needed...

All the best,

Peter

The 425's are plumbed differently, as SnowRidge so aptly described.

On the 400 series machines, each side has the front and rear wheel motors in series. The two series coupled sides are in parallel.

You can lift both front wheels off the ground using the bucket, and the tires will spin slowly, yet the rears will continue to push the tractor. Similarly, you can pucker the rear of the tractor, lifting both rear wheels off the ground, and the front wheels will continue to push the tractor.

You'd only lose propulsion completely if both the front an rear wheel on the same side were off the ground, and that circuit would get all the flow. Luckily, with the oscillation of the PT, that's almost impossible, unless you're in the unfortunate process of tipping the PT over on its side....

 

[ponytug]

I wish the scenario below were true for the 1445 that I have, but since the plumbing all comes back to two ports on a single pump, it is possible to get diagonal wheels off the ground and spinning, with no tractive force.

I won't say that you don't get some traction, but even having a single wheel spin on a steep slope is a major loss, a loss that I have always attributed to the single port issue.

I find it interesting that the lower flow variable displacement pumps have two pairs of ports that are independent, which is a very useful feature.

I have learned, the hard way, that when working with a stationary tool on a slope, e.g. a trencher, that it is best to set the parking brake and deal with the slippage of the tires on the slope, rather than actively trying to keep a position, which often deteriorates into a wheel spinning a hole. But that could just be a feature of my soils and/or my ineptitude.

All the best,

Peter

The 425's are plumbed differently, as SnowRidge so aptly described.

You'd only lose propulsion completely if both the front an rear wheel on the same side were off the ground, and that circuit would get all the flow. Luckily, with the oscillation of the PT, that's almost impossible, unless you're in the unfortunate process of tipping the PT over on its side....

 

[stray]

Once again thanks guys for the information and the energy you all have shown to help on this project.
In my thinking if excessive leakage were causing me not to be able to climb hills with a load it would be in the variable speed motor. I am guessing that it is not slipping more than its design lets it. I understand about just getting used to it but the Pt seems to climbing places as it always has.
Let us say that theoretically the pump was not bypass leaking at all, even at low speeds. I would think that one could ease down on the peddle and the Pt would climb a trees till a hose or something bursts. But as it is I keep pushing the peddle down and the motor compensates with more flow to overcome the internal leakage in the Hyd motor. Now I get to the point where the gas motor starts to bog but the tractor is not moving up the hill. Playing around with the peddle (a little more a little less) I teeter on not having enough flow and pressure to move the Pt on up the hill or killing the motor.
If the problem was say leakage in the wheel motors then there would NOT be the tendency of Killing the Gas motor. You would just be setting there with the peddle on the floor, Full throttle, and all the power you could muster, fluid bypassing the wheel motors and not going on up the hill, the gas motor not trying to die.
Now does this seem right or have I got it all wrong? Mabe leakage in the wheel motors can cause the Hyd motor to need to pump a higher volume leaving the pump in (for lack of better words) a higher gear. This just takes it right back around to Rips recommendations and maybe me still thinking my Pt is still doing close to what it was designed to do. Wow!!!

 

[BobRip]

Once again thanks guys for the information and the energy you all have shown to help on this project.
In my thinking if excessive leakage were causing me not to be able to climb hills with a load it would be in the variable speed motor. I am guessing that it is not slipping more than its design lets it. I understand about just getting used to it but the Pt seems to climbing places as it always has.
Let us say that theoretically the pump was not bypass leaking at all, even at low speeds. I would think that one could ease down on the peddle and the Pt would climb a trees till a hose or something bursts. But as it is I keep pushing the peddle down and the motor compensates with more flow to overcome the internal leakage in the Hyd motor. Now I get to the point where the gas motor starts to bog but the tractor is not moving up the hill. Playing around with the peddle (a little more a little less) I teeter on not having enough flow and pressure to move the Pt on up the hill or killing the motor.
If the problem was say leakage in the wheel motors then there would NOT be the tendency of Killing the Gas motor. You would just be setting there with the peddle on the floor, Full throttle, and all the power you could muster, fluid bypassing the wheel motors and not going on up the hill, the gas motor not trying to die.
Now does this seem right or have I got it all wrong? Mabe leakage in the wheel motors can cause the Hyd motor to need to pump a higher volume leaving the pump in (for lack of better words) a higher gear. This just takes it right back around to Rips recommendations and maybe me still thinking my Pt is still doing close to what it was designed to do. Wow!!!

This behaves just like my 422. I sometimes walk my PT up a hill by steering left then right over and over. It helps some. I think your machine is working OK. I did go from 5w30 to 15w50 synthetic oil in the hydraulic system and this helped a fair amount.

 

[SpringHollow]

"But as it is I keep pushing the peddle down" You want to be letting up on the pedal, not pushing harder. Use the throttle for speed.

Or am i missing something?

I know i routinely push harder - hard habit to break.

Ken

 

[J_J]

Once again thanks guys for the information and the energy you all have shown to help on this project.
In my thinking if excessive leakage were causing me not to be able to climb hills with a load it would be in the variable speed motor. I am guessing that it is not slipping more than its design lets it. I understand about just getting used to it but the Pt seems to climbing places as it always has.
Let us say that theoretically the pump was not bypass leaking at all, even at low speeds. I would think that one could ease down on the peddle and the Pt would climb a trees till a hose or something bursts. But as it is I keep pushing the peddle down and the motor compensates with more flow to overcome the internal leakage in the Hyd motor. Now I get to the point where the gas motor starts to bog but the tractor is not moving up the hill. Playing around with the peddle (a little more a little less) I teeter on not having enough flow and pressure to move the Pt on up the hill or killing the motor.
If the problem was say leakage in the wheel motors then there would NOT be the tendency of Killing the Gas motor. You would just be setting there with the peddle on the floor, Full throttle, and all the power you could muster, fluid bypassing the wheel motors and not going on up the hill, the gas motor not trying to die.
Now does this seem right or have I got it all wrong? Mabe leakage in the wheel motors can cause the Hyd motor to need to pump a higher volume leaving the pump in (for lack of better words) a higher gear. This just takes it right back around to Rips recommendations and maybe me still thinking my Pt is still doing close to what it was designed to do. Wow!!!

Stray,

You can not forget about the relief circuits on the pump. When you exceed the torque limits of the wheel motors, you will maybe hear the relief circuits in the pump operating. When you hear the engine start to lose power, it is probably working at or near relief pressure. If the relief did not work, the engine would stall , or something would blow out, be it pump, hose, or wheel motors. If you want to climb hills or whatever, then you need larger wheel motors, or larger engine, or larger pump with a larger engine, and larger wheel motors. You have to simply overcome the energy available for the weight you are trying to get up the hill. Why are motorcycle fast, Hp to weight ratio. Look at the hydraulic winch. straight off the motor shaft, you have so much pull, but run that shaft through a gear box, and you increase torque.

You have to realize, that a larger PT might not be able to get up that slope, because even though it has a larger engine, it also weighs more.

Go into this web site and use the hydraulic calculators to work some figures. With the same engine, same pump, by doubling the cu in of the wheel motors, you will double the torque. but you will lose some speed, as has been stated before.

Burden Sales Surplus Center - Tech Help

 

[SnowRidge]

I find it interesting that the lower flow variable displacement pumps have two pairs of ports that are independent, which is a very useful feature.

If you are referring to the PT-425 series, they don't have two independent pairs of ports. The left and right series coupled wheel motor pairs are plumbed in parallel by way of T fittings screwed into the pump's wheel motor ports.

 

[SnowRidge]

I would think that one could ease down on the peddle and the Pt would climb a trees till a hose or something bursts. But as it is I keep pushing the peddle down and the motor compensates with more flow to overcome the internal leakage in the Hyd motor. Now I get to the point where the gas motor starts to bog but the tractor is not moving up the hill. Playing around with the peddle (a little more a little less) I teeter on not having enough flow and pressure to move the Pt on up the hill or killing the motor.

I think you may have a bad tram pump. Your description sounds similar to that of Central_PA_Chris when his brand new machine couldn't climb up onto his trailer. His was obviously worse than yours, but there are certainly similarities. PT finally fixed the problem under warranty.

There should be an implement (wheel motor) relief valve that screws into the pump body. It may be bad, partially bypassing some fluid. It is located on the bottom of the pump, directly opposite the trunnion shaft.

For what its worth, I can tow my 2,400# trailer around with my PT, even up a mild incline. I also towed a small trailer with 60 gallons of water and a bunch of tools (roughly 1,000#) up my hillsides when I was planting Xmas trees. What you are experiencing just doesn't seem right.

 

[ponytug]

Thanks for being the straight man!

This is my point: the hydraulic fluid will always flow to the the wheel with the least resistance, if it is plumbed in common. And, apparently, all of our tractors are plumbed in common. Powertrac would have had to install some rather expensive flow matching devices to create separate circuits.

SO, the tractors will climb the best when all four wheels are on the ground, and in good contact with the earth. Slippage of any one wheel will unload all of the wheels.

All the best,

Peter

If you are referring to the PT-425 series, they don't have two independent pairs of ports. The left and right series coupled wheel motor pairs are plumbed in parallel by way of T fittings screwed into the pump's wheel motor ports.

 

[ponytug]

Stray,

I don't think you have a leaking motor or pump by your description. I would have to say that you are close on your description below, but not quite totally on the money.

I would like to clarify one point, which has been extensively discussed elsewhere. The drive pump for power-tracs is a Variable Displacement Pump. (Check out the animation, I think it will help explain the action of the pump.) These are special pumps that can vary the amount of oil pump from 100% to 0% to -100%. (i.e. full forward to stop to full backward). This means that if the engine is going at full speed (Wide open throttle, WOT), all of the peak horsepower can be applied to pumping 0-100% of the flow. If you are creeping up a hill, with only a little bit of hydraulic flow, then the pump needs only to be pumping that limited volume plus whatever gets lost in the pump or drive motors. If you try to pump more oil that the required amount, then either the reliefs will open and dump oil, or the engine will start to slow down. With extra load on the engine, the engine speed slow more, you loose horsepower, and the engine slows more, until the vicious cycle stalls the engine, or you let up on the treadle.

So, the best strategy on hill climbing with a PT (or anything else with a similar drive) is to have the engine at peak horsepower, (WOT), and just enough pedal pressure to just barely slow the engine, keeping the engine running at peak horsepower.

Oh one other thing-you want to keep all four wheels on the ground.

I hope that this helps.

All the best,

Peter

P.S. My limit on hill climbing is loss of traction; my soils just break loose, and the wheels spin. Somewhere around 20 degrees, I have to shut down the draft control to get up the hill, adding another five degreees, and I have to shut the PTO down as well. If I could keep the wheels from slipping, I probably wouldn't have to shut anything down... I need to upgrade to either duallies or chains, but so far, I haven't done it, as both are expensive (about the same cost, funnily enough).

Once again thanks guys for the information and the energy you all have shown to help on this project.
In my thinking if excessive leakage were causing me not to be able to climb hills with a load it would be in the variable speed motor. I am guessing that it is not slipping more than its design lets it. I understand about just getting used to it but the Pt seems to climbing places as it always has.
Let us say that theoretically the pump was not bypass leaking at all, even at low speeds. I would think that one could ease down on the peddle and the Pt would climb a trees till a hose or something bursts. But as it is I keep pushing the peddle down and the motor compensates with more flow to overcome the internal leakage in the Hyd motor. Now I get to the point where the gas motor starts to bog but the tractor is not moving up the hill. Playing around with the peddle (a little more a little less) I teeter on not having enough flow and pressure to move the Pt on up the hill or killing the motor.
If the problem was say leakage in the wheel motors then there would NOT be the tendency of Killing the Gas motor. You would just be setting there with the peddle on the floor, Full throttle, and all the power you could muster, fluid bypassing the wheel motors and not going on up the hill, the gas motor not trying to die.
Now does this seem right or have I got it all wrong? Mabe leakage in the wheel motors can cause the Hyd motor to need to pump a higher volume leaving the pump in (for lack of better words) a higher gear. This just takes it right back around to Rips recommendations and maybe me still thinking my Pt is still doing close to what it was designed to do. Wow!!!