Do any tractors have true 4wd? Seem like they always call the powered front driveline something else. Is that branding or some other reason? Do any have front and read wheels that spin at the same speed or is that all part of the issue?
4wd?
- Thread starter Surgeon
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The big ag tractors have true 4wd while the smaller ones have front wheel assist. On them the front wheels turn slightly faster than the rears when engaged. This is why the manual will say to not drive in 4wd on hard surfaces.
brain55
Veteran Member
Not sure exactly what the question was I think there are a couple in there. Yes, there are true 4wd tractors. You probably won't find it in CUT's, rear diffs will be open carriers w/diff lock and fronts will be open carriers also meaning in limited traction situations you will likely at the most have 3wd. As you get into larger machines you will start to see limited slip diffs in the front, I have even seen mechanical diff locks in the front.
Now as far as wheel speed front and rear with different size tires front and rear there will only be a small window where speeds are matched because of tire wear and varying inflation pressures. The factory tries to match it as close as the can with gear ratios that is why they don't recommend using 4wd on hard surfaces.
Now as far as wheel speed front and rear with different size tires front and rear there will only be a small window where speeds are matched because of tire wear and varying inflation pressures. The factory tries to match it as close as the can with gear ratios that is why they don't recommend using 4wd on hard surfaces.
Opti-Mist
Platinum Member
Generally speaking, the equal sized front and rear wheels would be 4WD while the unequal sized (front being smaller) is Front Wheel Assist. In the latter case the front wheels tend to turn just a bit (5%) faster than the rears by design.
I watched a friend in his Jeep Rubicon lock his diffs and pull out a neighbor's Kubota that I could have never budged with my MFWD tractor despite my tractor weighing more and having chains. He told me that my front end would always spin and break through because I only have 3wd and the front spins faster than the rear. ...so I was thinking about it (it was bugging me) and knew someone here would know the answer.
scrappy isb67
Gold Member
they are ALL MFWD (Mechanical Front Wheel Drive) doesn't matter if it is a 1023e all the way thru the 8r series. and unless the tractor has all 4 tires the same size( a 9r series), there will always be a slight overdrive to the frontend. the major difference is the open diffs on the front of the little ones vs lockers/limited slip diffs in the big ones. even some of the bigger 4wd (equally sized tires) have some gear lead in the frontaxle.
We have two different 4WD tractors- I have a Kubota B7100, and my father has a NH3930. The front tires do not lead, or rotate faster, than the rear tires. If they did, you would get tension even when going in a straight line, and either the front tires would spin, or the rears would drag. Neither does this. I don't know where you get your information that the front tires lead by a percentage, but it is due only to a difference in tire sizes- where there is a discrepency in the ratios, say due to under or overinflated tires. Again, the difference in rotational speed would manifest itself, especially the farther you travel and/or faster you travel. The only way it would be possible is if there is a differential in the transfer transmission, which would absorb the difference. Neither of ours do. Simply, 4WD is a 100% mechanical link up of the rear and front axle. Regardless of the terminology, both of our tractors, and any other 4WD tractor that I have had experience with, was a 100% mechanical link-up 4WD. Backhoes, articulated tractors and wheel loaders, telehandlers, etc. all work in the same way- many of them can't even be disengaged from 4WD.
The tension that is generated by a 4WD tractor is not from a difference in rotational speed between the front and rear, but a difference in the turning arc. Because the front tires turn left and right, they follow a different length arc in a turn than the back tires. A difference in distance travel when the front and rear tires are turning will cause a mechanical bind, because they are 100% mechanically linked.
And, a 4WD tractor is exactly that-4WD. There are differentials in the front and rear, for a good reason. These differentials allow traction to be lost on the tire with the least traction, because of the differential action. If the two tires have the same amount of traction, both will spin. The same for the front. So, on a vehicle, whether tractor, or atv, or truck, or whatever, if it is 4WD with no locking differentials, all 4 tires will direct power to the ground unless there is unequal traction. Then, you have a 2 or 3WD vehicle. The only way to overcome that, as mentioned with the Rubicon Jeep, is to have differentials that lock. Most 4WD tractors have a locking rear, but not a front. If they were both locked permanently, it would be a nightmare to drive. I would imagine that manufacturers haven't addressed and started offering locking front differentials on tractors is the lack of need- most of the time, traditional 4WD is more than enough. It keeps costs down, and simplifies things. I understand that some large tractors have the option, but I'm not familiar with it on smaller tractors. I haven't found it to be necessary on either of your tractors. Traditional 4WD with a locking rear has been more than enough. We aren't rock crawling with them- 3 and 4WD has done the job well.
The tension that is generated by a 4WD tractor is not from a difference in rotational speed between the front and rear, but a difference in the turning arc. Because the front tires turn left and right, they follow a different length arc in a turn than the back tires. A difference in distance travel when the front and rear tires are turning will cause a mechanical bind, because they are 100% mechanically linked.
And, a 4WD tractor is exactly that-4WD. There are differentials in the front and rear, for a good reason. These differentials allow traction to be lost on the tire with the least traction, because of the differential action. If the two tires have the same amount of traction, both will spin. The same for the front. So, on a vehicle, whether tractor, or atv, or truck, or whatever, if it is 4WD with no locking differentials, all 4 tires will direct power to the ground unless there is unequal traction. Then, you have a 2 or 3WD vehicle. The only way to overcome that, as mentioned with the Rubicon Jeep, is to have differentials that lock. Most 4WD tractors have a locking rear, but not a front. If they were both locked permanently, it would be a nightmare to drive. I would imagine that manufacturers haven't addressed and started offering locking front differentials on tractors is the lack of need- most of the time, traditional 4WD is more than enough. It keeps costs down, and simplifies things. I understand that some large tractors have the option, but I'm not familiar with it on smaller tractors. I haven't found it to be necessary on either of your tractors. Traditional 4WD with a locking rear has been more than enough. We aren't rock crawling with them- 3 and 4WD has done the job well.
brain55
Veteran Member
Thanks Hodge, you said more eloquently what I wanted to say.
Buckgnarly
Platinum Member
The 4:1 low ranger transfer case did not hurt in this case....I have a Rubicon, and when both axles are locked and in low, that thing can PULL like no other!
LD1
Epic Contributor
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.
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.
Buckgnarly
Platinum Member
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
Veteran Member
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
Elite Member
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
Platinum Member
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
Platinum Member
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
Epic Contributor
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
Platinum Member
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
Epic Contributor
This is a quote from firestones website when talking about MFWD tractors.
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
Platinum Member
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
Epic Contributor
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??
