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.
