Question on PT drive function under slippery conditions

[m5040]

On the gas engine machines (esp PT180), if your operating in slippery conditions or if you raise the front wheels off the ground with the bucket, does the rear axle still drive 100%? Or do you notice a drive reduction when one wheel slips or wheel(s) off ground? I hear the older models where plumbed in a way that if one wheel was off ground or on ice, only that one wheel would drive.

We have all seen this

Power Trac PT180 with bucket - YouTube

 

[m5040]

No comments?

 

[joshlee]

I know your asking about the gas machines, which I don稚 have. But, I do have a PT 1430 and it drives with only one wheel in the front, while at the same time driving one in the rear. If the front wheels are off the ground, I?m not shure if the rear wheels drive 100% ?

Josh

 

[Rustyiron]

^^^^^ so in other words, there's a drive motor on each (conventional) drive axle that has an open differential?
I have become curious about the PT machines due to the guys here on TBN with them and their devotion.

 

[Joe Malovich]

It's my understanding that a front motor and a rear motor are in series which means fluid must flow through one pump before the other, typically sharing the load and pressure drop in the line. If one motor has no load then the rear motor sees 100% of the load while spinning at the same RPM. I don't know if they are plumbed in a cross-fashion like your car's brakes or not.

Disclaimer this is what I've read elsewhere, possibly relating to steiners and ventracs, I don't own a PT.

 

[m5040]

Great, that is what I was hoping for. It appeared the PT180 in the video was able to drive with the front axle light loaded or off the ground. I was told that the older machines would loose all traction if one wheel was raised, like they were plumbed in parallel. (One reason I didn't go for that used red 425, since it was around a 1990 model and was expected to operate that way).
Just for thought, Moffett fork trucks are hyd drive and would loose all traction with one wheel spinning, but they have what they call a differential lock, which is basically a flow divider, equally to all three wheels. If someone wanted to install 2 valves on a PT and go straight, it would act like locking axles. Don't know how much you guys get stuck, it would be good to have and really not that expensive (when you compare to installing lockers in a differential).

 

[joshlee]

That is interesting. That differential lock would be nice at times when my PT is in a bind where one of each of the front and rear wheels is off the ground. Those wheels that are off the ground spin and the machine does not go anywhere. Having said that, I could always, so far, get traction by turning the steering wheel or using the FEL in some way to get better traction.

 

[MossRoad]

There are no differentials. There are 4 wheel motors, one at each wheel.

The left front and right rear are in series.
The right front and left rear are in series.
That makes two wheel circuits.
The two wheel circuits are hooked together in parallel.
This is so the machine can turn.

If you're not moving, and you turn the steering wheel all the way to the left, the two left wheels will roll TOWARDS each other as the two right wheels will roll AWAY from each other.

The front left will roll backwards, as will the right rear, and the left rear will roll forwards as will the right front.

Various forms of this movement happen wether you're standing still, moving forward, moving backward, varying speed, etc...

The series and parallel circuits all work in unison.

If a wheel loses traction, the opposite corner wheel will still move the machine as long as it has traction.

If you lose traction at both the left front and right rear, that circuit will get full flow and you'll stop moving, because it is a parallel circuit to the opposite circuit.

Series uses the path of most resistance.

Parallel uses the path of least resistance.

With that said, I've never, ever, been stuck in 18 years of abusing this machine. Even deep snow I've always been able to just drive forward and backwards and drive out. I have had to do the wiggle, waggle with the steering wheel a few times in mud, but that's about it. Always got out.

I did drop off of a hidden log like a ski jump probably a good foot in diameter going down hill in thick brush and high-centered the machine one time. I could not push the brush hog down far enough to lift myself off the log.

 

[MossRoad]

I forgot that I also dug a hole so deep a few times that I dropped the front wheels in and couldn't back out, so I used the bucket to push myself out.

 

[m5040]

Sounds cool and logical to be soft on turf, but that raises my concern about when you use down pressure on the loader bucket to make a cut or to back drag, if the front axle gets light or raises, the machine stops due to the X pattern and both front wheels would spin. Guess I will try one out eventually at Tazewell.