4x4 ?

[Mark Page]

I've probably owned 6 4wd vehicles over the past 20 years. Pick Ups, SUVs etc. Everyone would buck when you tried to turn in 4wd. With the 4wd engaged my new Massey 2615 w/mfwd will not buck no matter how sharp you turn or what speed. Why is this?

 

[murphy1244]

I've probably owned 6 4wd vehicles over the past 20 years. Pick Ups, SUVs etc. Everyone would buck when you tried to turn in 4wd. With the 4wd engaged my new Massey 2615 w/mfwd will not buck no matter how sharp you turn or what speed. Why is this?

You sure your really in 4 wheel?

 

[Soundguy]

does it use cv type front axles ?

 

[JerryG]

On tractors the front gears are faster than the rear. Thus the front is pulling the tractor a small amount faster. On a auto the front and rear use the same ratio or extremely close.

 

[Raspy]

It probably because you are on dirt and because the rear has much more traction than the front. Also, there are no springs to allow windup or bouncing. So the front slips a bit and it's no big deal. Mine does the same thing, smooth on turns even in 4WD. I notice that there is some slipping going on, but it doesn't jump like my my pickup does.

The axle ratios are not designed to make the front pull the tractor. The difference in speed cannot be corrected with a ratio difference because the speed difference is dependent on how sharp you turn. It's always a different ratio between the front and back. They are designed to run smoothly when going straight with the correct ratio for the different size tires.

 

[andrehoude123]

Also if you don't have your diff locked up in the back it's only a 3x4 so your 2 front wheels and one back wheel and it's usually the outside one turning in a corner witch pushes you thru the corner my l45 will not but on 4x4 but in 4x4 with the diff locked up its a rough corner

 

[mikehaugen]

Also if you don't have your diff locked up in the back it's only a 3x4 so your 2 front wheels and one back wheel and it's usually the outside one turning in a corner witch pushes you thru the corner my l45 will not but on 4x4 but in 4x4 with the diff locked up its a rough corner

This is kind of a misconception. An open dif applies equal torque to both wheels at all times. If there is no wheel spin, both wheels have power... even in a turn.

 

[DarkBlack]

That is true. Equal torque, but likely unequal power. Confuses almost everyone.

 

[LD1]

4x4 is 4x4 no matter what combination of open diffs, lockers, posi's, or spools. You may only see 2 wheels spinning, but the other two wheels are trying to drive with the exact same amount of force as the ones spinning.

True, in can be unequal "power" if we are talking horsepower. but just "power" is too broad of a term.

Horsepower is 0 if there is no rotation. So while torque is being applied to try to turn the wheel, if traction is great enough that it dont spin or roll, then yes, technically, there is no horsepower.

As to why the tractor dont buck like a truck, I think it is a combination of what most others posted. First, the fronts do rotate a tad faster, so that helps. But with everything being ridgid and no suspension, they just slip and you dont know.

There were/is exceptions to the trucks though. Old full time 4wd trucks with a 203 t-case didnt buck, cause they had a differential gear in the t-case just like the axles. It allowed one axle/driveshaft to rotate at a different speed.

 

[mikehaugen]

Have you tried it on pavement?

 

[dieselcrawler]

I think the suspention has a lot to do with it, or lack there of, in the case of a tractor. With the 3005 front axle engaged on pavement I can tell the front tire (s) are slipping a small amount but it doesn't buck due to there not being springs to compress and rebound. Same is true with pulling trucks in the pitts at the county fair... tire with the least traction just slips, normally the rears in that case, due to motor weight and front lockers/spools and little to no suspention.

 

[Raspy]

Also if you don't have your diff locked up in the back it's only a 3x4 so your 2 front wheels and one back wheel and it's usually the outside one turning in a corner witch pushes you thru the corner my l45 will not but on 4x4 but in 4x4 with the diff locked up its a rough corner

There is no such thing as 3 wheel drive.

Open diff means equal torque always to both wheels on an axle, but uneven speed.

Locked diff means unequal torque to both wheels on an axle, but always equal speed.


Look at this video, it's great:

How Differential Gear works must see 100% - YouTube

 

[JasG]

I've probably owned 6 4wd vehicles over the past 20 years. Pick Ups, SUVs etc. Everyone would buck when you tried to turn in 4wd. With the 4wd engaged my new Massey 2615 w/mfwd will not buck no matter how sharp you turn or what speed. Why is this?

A couple reasons I can think of. As already brought up the front wheels are spinning faster (faster ground speed) than the rear. The older 4 wheel drive tractors would "buck" as you put it, like the oldest IH 66 series. Older tractors were much like truck, same ground speed, no planetary, single U-joints at the wheels. The newer tractors I have driven have a doubled up U-joint at the wheel where truck would have a single at each wheel. This doubled joint gives it 2 pivots and eliminates the binding. I believe this is called a double cardan joint or shaft.

Item 10 in the 5th picture is the front axle shaft assembly and you can see the 2 U-joints out at the end of the shaft. This gives a much tighter turn without the binding hop.
Tractor parts and attachments: Dana front axle

If you drive in 4wd on a concrete floor, the front tires should leave a mark on the floor. Or if you can shift on the fly you can feel the fronts come on, on a 4wd. This would be from the 2%-5% faster ground speed the tires should have.

Smaller utility and compacts use a different front axle altogether that allows a very tight turn with no binding.

 

[Mark Page]

Dosen't seem to matter what surface it's on. Macadam drive or grass or stone.

 

[JasG]

Dosen't seem to matter what surface it's on. Macadam drive or grass or stone.

With the bucking you refer to it won't matter what surface you drive on. If you drive on concrete though in a straight line in 4wd your front tires should leave black marks from the fact they are spinning at a faster ground speed than the rear.

 

[Gary Fowler]

The tires dig much more in a turn in 4WD than in 2 WD. I think this is the reason you don't feel the bucking as they just dig into the dirt. I can tell by the sound it makes in 4 WD if on a hard surface that it is somewhat binding up due to different rotational speed from front to back. I know the fronts are constantly spinning from the wear on the fronts with non on the back of my LS. It isn't as obvious on the Kubota I think due to the R4s and much lighter tractor. I think the bucking is as others have stated, more U joints and springs to wind up on an automobile while nothing on the tractors.

 

[dave1949]

I can feel a little bucking on my NH TC40 on hard dirt with a load in the bucket and a making tight turn. I try to avoid that with more gentle turns or shift to 2WD.

I assume the load and surface make it harder for the front wheels to do the normal slipping.

 

[BHD]

I do not know how tractors are set up, but some of the old military trucks, had a over running clutch in the transfer case, that only engaged the front axel when it was slipping, and when put in reverse there was a shift lever in the case that switched to the reverse clutch, and they do nt crab either but the all wheel drive is operatable when any time the rears are turning faster than the fronts, by a few percent, other wise they were basically just free wheeling

the other possible is s transfer case differential

It is possible this type of design could be incorporated in to your tractor,

 

[ksbrdmkr]

Most CUT front drive is of the drop spindle type? where my larger 4x4 tractor has a straight front axle with u-joints that do buck when turned to tight.