... sorry, I couldn't help it :D
Greetings : I've been looking far and near on the cyber treads trying to find 4wd specifics. Been a 4wd drive owner for 40 of my 60. Truck and tractor. All been get wet and lock to the toggle from the cab lock. Up to this point I have known the do's and wish I didn't. Well I cannot determine whether the new JD 758 4wd will be able to cut grass while turn and return on dry pavement. It appears it is full time. Any you folks have any suggestions or comments. Thanks
My understanding is similar to others.
This is my general guide, but there are no set rules. This is based on the "common" usage of terms around here.
4wd/AWD - is the large tractors that all 4 tires are the same size. They may steer by wither turning the tires or articulation of the frame.
MFWD - Mechanical front wheel drive, or assist. These are row crop all the way down to the small compacts. You can select to put power to the wheels or not. As others have said, my understanding and experience is the front tires turn a little faster than the back. Kubota even has "bi-speed" where once the wheels turn past a certain point they speed up even more. Deere has "caster action" which the front wheel lean into a turn which for a couple of reasons helps with turning. Some have called it others things some have open, limited slip or locking front ends.
HFWA/HFWD - Hydraulic front wheel assist is a system like some road graders have where hydraulic motors are used in the front wheels. This gives a very tight turn. The problems were because the rear tires were driven by the trans and the front by hydraulics the speed difference was usually a large amount. The Deere system had a 2 speeds but you also had large changes with engine speed. This was used on the 20, 30, and 40 series Deere row-crop tractors. I believe Oliver and Allis Chalmers among others also had systems similar. The biggest problem was if left on it would get very hot and put enough power to the tires. It is still used today on most brands of combines and forage harvesters, but both ends are hydraulic driven. That seems to work much better being the system isn't fighting it's self.
There are some less common systems out there.
This is on the front tires being faster.
Frequently Asked Questions | Firestone Agricultural Tire
Mechanical Front Wheel Drive tire recommendations for best performanceQuote:
The problem could be the result of "lead/lag," a condition found on MFWD tractors that can shorten the life of the front tires and cause wear and tear on the tractor's transfer case. Lead/lag refers to the relationship between the speed of the front wheels and the speed of the rear wheels. If the front tires' speed is faster than the rear tires' speed, the tractor has a lead condition. If the front tires' speed is slower than the rear tires' speed, the tractor has a lag condition. The desired amount of lead is 2 percent, which means the front wheels turn 2 percent faster than the rear wheels. The Firestone Farm Tire Data Book contains information about how to accurately measure and correct lead/lag on your tractor, or you can click here. Rapid MFWD front axle wear can also be caused by misalignment (toe-in) or worn tire rods.
Mechanical Front Wheel Drive (MFWD) tires are designed to travel faster than the rear tires. This reduces front tire wear, improves front wheel traction, reduces transmission wear from gear "windup," and allows easier shifting of the MFWD.