PT AL-629 ( can it be done ? )

   / PT AL-629 ( can it be done ? ) #41  
KentT said:
JJ,

First of all, it is a variable displace tram pump, not a fixed displacement pump.

Second, it isn't "something for nothing" -- it is trading off speed for torque, a common calculation and "balancing act" done in hydraulic systems, whether it be motor speed or reaction time of a hydraulic cylinder.

Third, the White wheel motors are rated for 3000 PSI, twice what they appear to be running now...

I'm not sure what the tram pump is rated for... nor am I sure how well the wheel motors will stand up at that pressure AND the wheels reversed.

But, as long as I don't damage the tram pump, I have little to lose -- because the only alternative I see for making the PT-425 useful for me is to replace those wheel motors with higher torque ones anyway...

I also find it interesting that you weren't a naysayer when Stray was originally discussing his mod:

http://www.tractorbynet.com/forums/power-trac/69056-two-speed-modification-pt-422-a.html
'

You know that I know that the tram pump is a variable displacement pump. The other pump was an example. You keep talking about pressure, that is a non issue. The pressure is what it is, whether it is in series or parallel. I have looked at variable displacement hyd pumps, and some of them run in the 3000 to 3500 psi range. I see no reason why you would damage your tram pump, unless pieces of o-rings, or pieces of metal, or just dirt from opening up the hydraulic lines. You know that the tram pump is the only pump that gets filtered before the fluid gets to the pump. The rest of the pumps draw fluid from the tank. If you want more torque, you increase displacement, which in turn will lower rpm, and therefore overall speed. As for Stray's project, he did not mention anything about changing pressure. You do have another option, and that is two speed motors. I don't feel that I have mis-stated anything that I have said. I have 33 years of being wrong 50% of the time, but that also means that I have 33 years of being right 50%of the time. I hope you figure out, if that project is feasible. I am wiling to help, just ask.
 
   / PT AL-629 ( can it be done ? ) #42  
J_J said:
'

You do have another option, and that is two speed motors.

JJ, the two speed motor actually seems like the easiest and most satisfactorily solution, especially if they just bolt on. Even with an adapter plate, it should be fairly easy. Does anybody have an approximate cost on these motors?
 
   / PT AL-629 ( can it be done ? ) #43  
BobRip said:
JJ, the two speed motor actually seems like the easiest and most satisfactorily solution, especially if they just bolt on. Even with an adapter plate, it should be fairly easy. Does anybody have an approximate cost on these motors?

Approximately $650 each, as I recall, per a local company. I'm sure they could be found for less...

I think these were also the ones with brakes, but I'm not sure. I priced several alternatives, including having Terry cut off the old-style mounting brackets and put on the new PT-425 motors...
 
   / PT AL-629 ( can it be done ? ) #44  
J_J said:
'

You know that I know that the tram pump is a variable displacement pump. The other pump was an example. You keep talking about pressure, that is a non issue. The pressure is what it is, whether it is in series or parallel. I have looked at variable displacement hyd pumps, and some of them run in the 3000 to 3500 psi range. I see no reason why you would damage your tram pump, unless pieces of o-rings, or pieces of metal, or just dirt from opening up the hydraulic lines. You know that the tram pump is the only pump that gets filtered before the fluid gets to the pump. The rest of the pumps draw fluid from the tank. If you want more torque, you increase displacement, which in turn will lower rpm, and therefore overall speed. As for Stray's project, he did not mention anything about changing pressure. You do have another option, and that is two speed motors. I don't feel that I have mis-stated anything that I have said. I have 33 years of being wrong 50% of the time, but that also means that I have 33 years of being right 50%of the time. I hope you figure out, if that project is feasible. I am wiling to help, just ask.

The whole premise of Stray's low-speed mod is that the pressure is doubled at the wheel motors... I don't know how you missed that, but you must have....
 
   / PT AL-629 ( can it be done ? ) #45  
I'm lost... :confused:

What exactly are we trying to accomplish in this project again?

As I understand it, the PT currently has one variable volume pump that powers four wheel motors.

There are two series circuits with two motors in each circuit.

Both of those series circuits are connected in parrallel.

This setup allows for the fantastic abilities of the PT to articulate without skidding the tires. That is, with the PT standing still and the steering wheel turned all the way to the left, we can turn the steering wheel all the way to the right and as we do this the right tires rotate towards each other while the left tires rotate away from each other. None of the tires skid on the grass. What is even more amazing is that we can also do this while the tractor is in motion, forward or reverse.

Now why do we want to mess this up? What do we gain?? :confused:

If we want more torque, and are willing to cut down the top speed, why not just change out all four wheel motors for larger cubic inches and keep the series/parallel setup?

If we go through the trouble of valving and plumbing to make it so we can switch between all motors in series, or the series parallel setup, we will essentially be creating a skid steer. What stresses will this put on the wheel motors, motor mounts, center pivot point, steering cylinders, etc...

I think those components will be subjected to stresses they were not designed for and things will start stressing out and failing quickly unless the machine is driven on slippery surfaces entirely.

I've been around many a 4x4 that someone forgot to release the lockers on pavement and snapped stuff. Skid steer tires and rims are designed for those stresses. The PT rims and tires are not. I've managed to rip a drive wheel off my PT425, in sand with the current series parallel circuit and the old style wheel motors. If I can do it with the "weak" wheel motors and the series parallel setup, my guess is if we go ahead with this mod and give the machine the ability to lock the wheel motors together, we will experience more tires ripped off the rims. Let's hope that is the only damage we see. ;)

I am in no way trying to discourage anyone from playing and experimenting with the machine. It is a tinkerer's dream. Just be aware of some of the problems you will encounter. Best of luck with the project. I am amazed at the things we PT owners come up with. :)
 
   / PT AL-629 ( can it be done ? ) #46  
MR,

Here's the original topic on that initiailly described Stray's proposed 2-speed mod:

http://www.tractorbynet.com/forums/power-trac/68493-travel-pump.html

What I'm planning to do is test the concept of the low-speed part of that proposed mod. BTW, according to Blackwell in that thread, Tazewell once made 2-speed PTs...

I don't think this will "lock" the wheels, when it comes to turning. I think when articulated the inside wheels will essentially pull the outside wheels, dropping the pressure there, then greater volume of fluid will go to the low pressure created there, and those outside wheels will "catch up"... but that is purely speculation, based on my understanding of hydraulics, such as it is. It certainly should not act like a mechanical 4WD with locked hubs, because they at least are "viscous coupled" instead of truly, mechanically locked.

I acknowledge that I will be losing the "posi-traction" feature that the series circuits provide. However, the vast majority of cars and trucks on the road do not have posi-traction, and it doesn't render them useless... In fact, they work just fine with a few exceptions, such as wet, slippery slopes. Of all the 4WD trucks I've had, only one, in fact had a limited slip rear differential. One other old Ford had the manual-locking front hubs that you describe. Somehow they all got the job done for me, though they might not have been the optimum configuration.

As I've said before spinning for me is typically not a problem at all with four loaded tires. If I spin at all, it is typically because of hydraulic downpressure on a front implement lifting the weight off the front tires -- and that is easily corrected by operator intervention. Combine that with the articulation AND oscillation of the PT and I believe that there will remain enough weight on each wheel almost all the time that spinning will not be a serious problem. The only times I have ever had a PT's wheel come off the ground were operator induced and correctible -- the articulation and oscillation have taken care of keeping all 4 wheels planted on the ground otherwise.

Since Stray is willing to donate the hydraulic manifold he made, I can test this premise for the cost of hydraulic hoses... which I plan to do. As long as I don't damage the tram pump, like I said, I have little to lose and much to potentially gain. My PT simply will not work on about about 1/2 of the areas I need to work on, once the hydraulic oil gets hot -- and that's after replacing the hydraulic oil with 20W50 Amsoil synthetic.

Here's a view down my back driveway toward where my house will be located (where the pile of topsoil is).

http://loonlanding.info/images/a-june_06/a-Img_0015_800.jpg

When hot, I have had to waggle the PT to climb that driveway will a loaded bucket. There are some areas of the lot that I cannot climb with a loaded bucket when it is hot. However, my little Simplicity machines will climb all over this area, though they are not as stable going across the slope. I can pull a loaded trailer of mulch up those slopes with them, in low gear. IMO, the performance of the PT with its old-style wheel motors simply isn't acceptable, as it is, in these work conditions, once the hydraulic oil gets hot...

BTW, my PT has virtually the same hours and is the same specs as yours. I think there's only a few months difference in age, in fact...

As far as why try it? Why would someone put a lower geared rear ring/pinion in their truck to get extra pulling power rather than buying a new HD diesel... $$$$$$

The necessary hoses (only two more, though I plan to replace the existing six also when I do it since they're now 6 years old) will cost less than 1/10 what four new wheel motors will cost, especially since there's little market for four used lower-torque wheel motors with only 375-400 hours on them. :D
 
   / PT AL-629 ( can it be done ? ) #47  
How steep is that hill? I've got a fairly steep hill that I cannot run my brush hog up, but can tram a heaping full large bucket up all day. I do agree that performance is diminished as heat goes up. That is a fact and I have experienced it first hand and wonder how much I could gain with stronger wheel motors. However, I do not want to lose any top end speed, as I use that tramming dirt from point to point and when plowing snow, especially on a return run, when empty.
 
   / PT AL-629 ( can it be done ? ) #48  
KentT said:
... since there's little market for four used lower-torque wheel motors with only 375-400 hours on them. :D

I'd give you $50.00 bucks for them. ;)
 
   / PT AL-629 ( can it be done ? ) #49  
I really don't know how steep that hill is -- I've never tried to measure it. Here's a few other views of it.

From the bottom, looking up:
http://loonlanding.info/images/quick_visit/IMG_0117_800.JPG

http://loonlanding.info/images/quick_visit/IMG_0132_800.JPG

From the side:

http://loonlanding.info/images/mulch/mm_18_800.jpg

The driveway goes up the point of the ridge, straight ahead:

http://loonlanding.info/images/a-june_06/a-Img_0001_800.jpg

With a LM bucket full of topsoil or wet mulch, it is all the PT will do to climb it when hot. As I said, I've sometimes had to waggle it to get "over the top."

It won't pull the same loaded Country Mfg cart up that hill that my 12HP Simplicity will in low gear -- something's wrong with that picture...

I had similar experiences mowing with it on the hill behind my barn in Massachusetts. Until I went to 20W50 the PT simply wouldn't climb it when hot. Now it will climb it, but not with the mower running. I go up and down it mowing with my Simplicities all the time...
 
   / PT AL-629 ( can it be done ? ) #50  
One other analogy I thought of regarding the loss of "posi-traction"... I should be no worse off than a normal 4WD CUT/SCUT without diff-lock engaged. How limiting is that for most things you'd be doing? IMO, though limiting, it is not "catastrophic"...
 

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