Tight turning with 4WD on

[TerryR]

There is alot of give and take about turning brakes and 4x4. These discussions never end well.

Really? I've been participating in this forum for 13 years and don't remember the subject every coming up. Maybe I wasn't paying attention?

What's the argument against using turning brakes while in 4WD?

 

[Farmer495]

Really? I've been participating in this forum for 13 years and don't remember the subject every coming up. Maybe I wasn't paying attention?

What's the argument against using turning brakes while in 4WD?

My experience is the tractor will practically pivot on one rear tire in 2wd, but in 4wd since the front tires are locked to the rear, the front tires can't speed up faster for the turn so it holds you back. I rarely have the brake pedals split on the 4wd unless I am in real tight quarters, or using my semi mount drill (tractor in 2wd to seed)

The 2wds I use turning brakes routinely.

Kubota has/had a bispeed front axle om some models that when you turned sharp in 4wd, the front axle upshifted and pulled you around.

 

[rScotty]

I have a JD 5055e. I know it's not good to turn sharp in 4WD in vehicles. Is this also true with tractors or should I not be worried about it?

TIA

Mechanics used to advise not to turn sharply in 4wd because all of the ways of transferring power through an angle from an axle to a wheel were limited by geometry. Most common solutions to what was called the "constant velocity steering problem" were variations on the Birfield or Rzeppa joints using caged balls sliding along a curved path. Those type joints do OK at high speeds, but don't last very long if they are cranked over at sharp steering angles. The picture explains why.


Sometime in the 1970s, Yanmar developed a practical low speed version of a dual bevel gear front axle drive that didn't care how sharply it is turned. In theory it could be turned 90 degrees or even farther without any binding or torque loss. Most compact tractors now use some variation of that dual bevel gear drive front axle. It will take full torque at any steering angle just fine.

rScotty

 

[Farmer495]

I have a JD 5055e. I know it's not good to turn sharp in 4WD in vehicles. Is this also true with tractors or should I not be worried about it?

TIA

Turn as sharp as you want on loose/slippery surfaces. No issue. Since front axle of tractor generally runs a few % faster than rear tires, front axle helps you turn. Can't run 4wd on hard surface (high traction), even in straight line

Pickup truck 4wd can run on hard surfaces in straight line since front/rear turns same speed, turning will bind it bad.

 

[Stonewall Cardinal]

You should only be using 4wd on slippery surfaces. regardless of your turning radius. If you are on an unforgiving surface like concrete or asphalt you shouldn't be using 4wd. If you are on a slippery surface, you can use 4wd and do tight turns, the necessary wheels will slip.

absolutely. I have very soft sandy ground and that is when I use it.

 

[Eagle1]

Every CUT I've been on has open diff in the front and back. Only way both wheels drive on an axle is to use diff lock on the rear. I'm sure someone has built one with limited slip or diff lock on the front axle but I have not encountered it. I get into the classic front right and rear left spinning frequently, just click in diff lock and off you go.

 

[TerryR]

My experience is the tractor will practically pivot on one rear tire in 2wd, but in 4wd since the front tires are locked to the rear, the front tires can't speed up faster for the turn so it holds you back. I rarely have the brake pedals split on the 4wd unless I am in real tight quarters, or using my semi mount drill (tractor in 2wd to seed)

I've never noticed that difference, but I rarely operate pavement or dry ground. Mostly on grass on hillsides, so brakes are needed for turning, 4WD or no, especially with the mower offset to one side.

I never operate in 2WD except on pavement, which is rare. I never lock the brakes together except when I am going to set them for a parking brake.

 

[npalen]

Turning in 4WD on pavement or even gravel or dirt to me is like scratching blackboard with fingernails!

 

[old and tired]

Why not?

It binds up the transmission... I guess if your transmission allows slippage, it might work. I can do it but it just drags the front end around. My front end is pretty light so it works but it's not happy. This is on a larger John Deere tractor at work... my little kubota doesn't need tight turning so I have not tried it.

 

[K5lwq]

It is really simple. If you need FWA use it. If you need to turn sharp do it. If you need to use the split brake to drag the front end around do that too. Now, the secret to all of this is be smart doing any of it. Slow down and use common sense. Problems come from doing these maneuvers with heavy loads on front end loaders and not thinking things through.