Combines Power Guide wheels

Yes, the manual is actually right on this. I too wondered the same when I first read it when looking on our 2188. It is especially helpful if you have to cut up and over hills, or terraces, and even just maneuverability in the field. Also, it'll keep you on top of the ground in marginal conditions too. My experience, Todd

Another reason in addition to those you mention is that it will keep your hydro drive pressures down thus keeping your hydraulic oil temperatures down. Works best if you also have the 2 speed hydro.

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Why soes it keep your hydro drive pressure downIJ looks to me like it takes a specific pressure for a given speed. Conversely it should(IJ) take more pressure to run 4-wheel drive for the same speed because of parasitic losses.

Best the reason the drive pressure is down is due to an increase in the surface area for the hydraulic pressure to work against. Granted we are still needing to move the same mass, but with an increase in surface area the pressure drops and still generates the same force. The math is FORCE GENERATED=HYDRAUlIC PRESSURE X SURFACE AREA in square inches. In other words the distance from the load to the fulcrum got shorter, the distance from the end of the lever to the fulcrum where I am pushing down got longer, I can lift the same weight with less force, but I sacrifice distance to do it. In the combine this distance is ground speed. Simple application of hydraulic principals and physics.

Hey Shellman, I really appreciate your response! If you don't mind, I have a couple more questions. I do not have a 4-wheel drive, but am trying to gain a better understanding of the hydro system in general. I understand the lower pressure_temperatures as a result of the larger surface area, at the expense of ground speed. How much lower is the ground speed with 4-wheel engagedIJ I would expect most folks are not willing to sacrifice ground speed during harvest for longer hydro life. Would the pressure in two wheel drive not be the same as a two wheel drive combineIJ If you run in 4-wheel and want the same ground speed, is going up a gear on the tranny an option, or does this reduce hydro and drive train life bcause of load due to higher gearingIJ Is this where the two speed hydro shows it's advantageIJ Can you briefly explain how the two-speed hydro worksIJ What dis-advantages do you have with the two-speed hydroIJ Hope you don't mind all the questions but this is a very interesting topic to me.

Well, I'm not shellman, but on our 2188, we lose about 1 mph when in 4wd. We do have the two speed hydro, and you can usually still run plenty fast through the field.

We'll give it a shot and see how it goes. My 1680 was a single speed machine and I put a new model (10 bolt hub) Mud Hog under it a couple of years ago. In second gear you could get about 7 mph max with 30.5_32. Engage the pga and max speed drops to about 5.2. Still within a usable range in the field on wheat as this is about the limit for the knife to cut the straw. Also worked pretty well in milo with yields around 100 bu+. You are correct in that with pga turned off the hydro does not know the difference in the machines. Only with pga turned on does the speed reduction happen. The pga motors are a radial piston design and are set up such that with the valve turned off they do not move up and down in their bores and require oil. We do continue to circulate oil from the charge circuit to cool the motors and oil. Same is true with the hydro drive motor. Once the charge circuit has been satisified and charge pressure drops and excess oil is circulated from the hydro motor back to the hydro pump and then to the cooler. The two speed motor has a variable angle swashplate very similar to the pump, however, the angle is set at one of two possible angles. As we decrease the angle of the swash plate the hydro motor displacement decreases and requires less volume and the output speed increases with the same oil flow input from the hydro pump. When in operation on the low side hydro pressures could go as high as 6800 psi (depending on model of combine). When in the high side of the two speed and drive pressures begin to exceede about 3500 psi, the response valve will shift and increase the angle of the swash plate and shift to low speed in order to keep drive pressures and heat down. I traded for a 2188 this December with two speed and transferred my pga from the 1680. I can't tell you for sure what the numbers would be, but I would expect that the speed loss will be less. How much will depend on tire sizes on the pga. The system allows the fluid to equalize between the pga and hydro motor. Hope this help, need more let me know.

Thank you very much! Your explanation was very clear to me. I appreciate you taking the time. In spite of my limited knowlege of the system, I have had my hydro apart on a couple of occasions for repairs. (new output shaft) To say I didn't know exactly what I was doing would be an understatement. It is pretty near impossible to troubleshoot hydro problems if you only have a limited understanding of how it works. Thanks again.