4wd?

[Buckgnarly]

Some mis-information in this thread I'll try to clear up :mur:

First, On tractors that have smaller front tires (that I am aware of), there is INDEED a lead percentage built into the system. And YES that makes the front tires slip a little. Just the way it is. I dont know where you are getting YOUR info from, but that is the way it is and is common knowledge amung 4wd tractor owners.

Second thing, it dont matter WHAT you call it, cause there is nothing set in stone. So MFWD, 4wd, AWD, front-wheed assist, etc are ALL used interchangebly.

Third, if you have one of the above mentioned 4wd, mfwd, etc. Tractors, and it has open differentials in front and rear, it is STILL 4WD. NOT 2WD or 3WD. That is incorrect termonology. IT is 4wd because ALL 4 wheels are STILL trying to drive the tractor. Sure, there is a time where a wheel or two may just sit and spin, BUT it is STILL trying to DRIVE the tractor. In an open differential, ALL wheels are attempting to move the vehichle with the EXACT same torque. IE: open diff means EQUAL TORQUE and UNEQUAL SPEED. But STILL, you have ALL 4 wheels trying to drive the machine with the EXACT SAME amount of force.

Using automotive world terms, AWD and 4WD are NOT the same.

An AWD car has some form of "slip" built into the transfer case, be it viscous coupler or mechnical means. A true 4WD will have the front and rear locked by means of gears or chain in the transfer case. There is no slip between front and rear axles, hence no driving(or more appropriately, TURNING) on hard pack surfaces while in 4WD but an AWD is OK. The slip is necessary b/c the front and rear axle will be turning at different rates due to different arcs while in a turn.

I am guessing that the makers of the 4WD tractors factor the tire size difference and adjust the front and rear gear ratio accordingly to get rid of as much rotational difference from front to rear. Even some OEM trucks have a slight difference (like 4.11 front and 4.10 rear )but if using on a slick surface it does not cause binding.

Open, L/S, and locked axles only affect the two wheels on that axle, not make it "4wd". The transfer case is what makes it AWD or 4WD.

 

[brain55]

Ok, much of it is semantics. As far as the lead being built into the front drive I'm going to disagree. In the 12 years I spent working as a mechanic in Kubota dealers and going to Kubota factory training the information I was given was that they tried to match the ratios as much as possible. Now in the decision process did they lean to the overdriven side on the front that is very likely considering front tires will wear faster than the rear changing their rolling radius and wear into the matched ratio, I'll buy that. The only time I know they were overdriving the front diff were in the bi-speed turn machines they made for a couple of years. They were mechanically shifting gears to drive the fronts faster after you turned the wheels a certain amount in order to make a smaller turning radius for mid-mount mowing tractors.

 

[mikehaugen]

I once had to re-do the dana 60 in the rear of my truck. It was a 3.54 (almost 3.55) ratio. I ordered a new gearset for it at it came and the ratio was right (close at least). Originally had 11 teeth on the pinion and 39 on the ring, what came was (IIRC) 9 teeth on the pinion and 32 on the ring. They come out to nearly the same ratio, but not perfect. I called the distributor and talked to a couple people and they all said it would be fine, I was skeptical but used it anyway. I works alright, but am very cautious about only using 4wd in the snow or mud or other slick surfaces.

 

[Buckgnarly]

I once had to re-do the dana 60 in the rear of my truck. It was a 3.54 (almost 3.55) ratio. I ordered a new gearset for it at it came and the ratio was right (close at least). Originally had 11 teeth on the pinion and 39 on the ring, what came was (IIRC) 9 teeth on the pinion and 32 on the ring. They come out to nearly the same ratio, but not perfect. I called the distributor and talked to a couple people and they all said it would be fine, I was skeptical but used it anyway. I works alright, but am very cautious about only using 4wd in the snow or mud or other slick surfaces.

Yes, some trucks that use mixed axles like Dana, Sterling, AAM, etc. have to use those "close but not perfect" ratios.....in the real world, even different PSI and tire wear can lead to bigger differences so it's rather negligible.

 

[wcampbell47]

I have a B7510 I bought in 2007. I can easily shift between rear wheel drive and all wheel drive on the fly without touching the clutch. So if there is a slight lead with the front tires it is insignificant .. else I would grind gears and have to use the clutch when shifting between RWD & AWD. Same holds true for my B3200 with HST. AWD is best not used on hard surfaces to reduce the strain on the front drive. To confirm just decrease your front air pressure, engage AWD and make a sharp turn on a hard surface. Normally your front tires will contort due to the strain. Even on hard packed dirt quite a bit of strain is placed on the front drive during turns in AWD. So lead or no lead save your front drive system and shift to RWD only when on hard surfaces and making lots of turns.

 

[LD1]

Using automotive world terms, AWD and 4WD are NOT the same.

An AWD car has some form of "slip" built into the transfer case, be it viscous coupler or mechnical means. A true 4WD will have the front and rear locked by means of gears or chain in the transfer case. There is no slip between front and rear axles, hence no driving(or more appropriately, TURNING) on hard pack surfaces while in 4WD but an AWD is OK. The slip is necessary b/c the front and rear axle will be turning at different rates due to different arcs while in a turn.

I am guessing that the makers of the 4WD tractors factor the tire size difference and adjust the front and rear gear ratio accordingly to get rid of as much rotational difference from front to rear. Even some OEM trucks have a slight difference (like 4.11 front and 4.10 rear )but if using on a slick surface it does not cause binding.

Open, L/S, and locked axles only affect the two wheels on that axle, not make it "4wd". The transfer case is what makes it AWD or 4WD.

Based on that logic, would you call the old "full-time" 4wd trucks that used the 203 T-case an AWD???


(The NP203 had a differential setup in it and in theory, on ice, it is possible that only 1 wheel would spin).

Anyway, arguing 4wd vs Awd vs MFWD vs FWA is a moot point. Right or wrong, they are use interchangeably. Kinda like saying you are going "bushhogging" when you have a woods cutter. Or crescent wrench, or channel locs, or vise grips, etc.

 

[Buckgnarly]

Based on that logic, would you call the old "full-time" 4wd trucks that used the 203 T-case an AWD???


(The NP203 had a differential setup in it and in theory, on ice, it is possible that only 1 wheel would spin).

Anyway, arguing 4wd vs Awd vs MFWD vs FWA is a moot point. Right or wrong, they are use interchangeably. Kinda like saying you are going "bushhogging" when you have a woods cutter. Or crescent wrench, or channel locs, or vise grips, etc.

If it has a method to slip in the transfer case it's AWD.

If it does not have a method to slip, it's 4WD.

You can call it whatever you like, but it does not make it proper.

 

[LD1]

Ok, much of it is semantics. As far as the lead being built into the front drive I'm going to disagree.

This is a quote from firestones website when talking about MFWD tractors.

The desired amount of lead is 2 percent, which means the front wheels turn 2 percent faster than the rear wheels.

And it you just do a simple search about "mfwd tractor lead and lag" you will get TONS of reading.

While I will admit, I have never seen a MFG specifically state lead and lag, (I havent really looked), these people cant just be making this up.

 

[Buckgnarly]

All this talk got me looking for a definitive definition, and it seems that SAE uses the two ranges to define 4WD and AWD.....it seems if it has a low range, they consider it 4WD....but only one range makes it AWD. Clear as mud I guess......:confused2:

 

[LD1]

If it has a method to slip in the transfer case it's AWD.

If it does not have a method to slip, it's 4WD.

You can call it whatever you like, but it does not make it proper.

Again, a moot point. Whether its rite or wrong, I dont care. I just understand that the terms are used interchangeably. It makes no difference to me, as I know what one is talking about either way. I am not about to go arguing with a 70-year old farmer who has been calling it one thing for all his life, and try to tell him he is wrong. Again, I just accept the fact that they are used interchangeably.

BTW, a vehicle or tractor that has 4 wheels and is 4wd, Isnt that ALL of the WHEELS DRIVING (AWD).

And what about a 4wd tractor with duals??