My wheels are definitely plumbed in series LL and RR (only ipsalateral side turns when up off all fours), but if one wheel starts spinning, most of the power goes to that wheel.
Shouldn't fluid follow the path of least resistance??? I didn't think it was a malfunction, just the nature of the beast.
Do your wheel motor have case drains? If they don't, it is impossible for most of the power to go to the wheel without traction. Since it doesn't have traction, it can't do any work and won't use any power, except for the little bit required to turn it over. Almost all of the power going to that side of the tractor will be used by the wheel that still has traction.
Remember, wheel speed is almost exclusively dependent upon hydraulic fluid flow rate. Wheel motors plumbed in series have to have the same flow rate, therefore they must turn at the same rate, therefore you can't have one spin while the other doesn't.
You may see a slight bit of wheel "cogging" as the pressure changes in the hose between the motors due to the unloading of the wheel without traction, but it will be limited to something less than a full revolution. The hose acts as a bit of an accumulator as it absorbs the increased pressure from the unloaded wheel.
Once a wheel breaks loose, more power is applied to the other wheel on that side, and there is some risk that it will also spin, even though it has more traction. Could that be what is happening?
If you do have case drains, the wheel without traction could be bypassing, sending a lot of fluid out through the drain. In that case, you would probably experience wheel spin.
My wheel motors do not have case drains, so I don't have any operating experience with that type and am merely hypothesizing.
Edit: I don't understand what you mean by
only ipsalateral side turns when up off all fours. I take ipsalateral to mean same or one side. If the machine is jacked up so that all four wheels are off the ground, all four should rotate at the same speed.
Ipsalateral! You must be in the medical field.
