Question on 4WD mode on BX23

[Speedy7]

I'm new to my BX23 and have a question on 4WD. I presume there is no mid or front differential, so I can expect binding on the wheels when turning on firm ground, etc.

While using it on dirt or grass, I notice that unless I am travelling in an absolute straight line, I can feel some slight shuddering on the drive train. I assume this binding, but I feel this even on slight and slow turns. Is this normal? I've taken to only putting it in 4WD mode when I really need it for the traction, and taking it after that.

Thanks!

SP

 

[aardvark]

There has to be a differential in there somewhere. When I lose traction without the differential lock engaged, the front and rear tires kitty-corner from each other spin. Once the lock engages then all four tires turn at the same rate.

I have noticed that when I turn very sharply, about as sharp as you can turn, the tires do scrub on hard surfaces. This is much more noticable after I have engaged the diff lock, and normally subsides a little when the diff foot pedal is released and the diff unlocks after a moment.

Anyway, it's normal. I live in a sandy area, so I just leave the 4WD engaged about 95% of the time. I normally only disengage 4WD when I mow.

 

[Speedy7]

You're right, I've had diagonal corners spin in 4WD mode as well, so there must be a front diff. So, could the slight shuddering I'm feeling be coming from the lack of a center differential?

 

[aardvark]

Maybe, although I suspect it has to do with the diff lock sticking a little, and more so with the turning radii of the BX. I think there is no steering ackerman, basically, both tires turn the same angle. In a car the outer tire will turn a smaller angle than the inner tire so both tires match the circlular path they are travelling on. I don't think the BX, or maybe tractors in general, have ackerman, most likely due to the hydraulic ram front steering. This will cause the front tires to scrub since the front inside tire is turning in slower than the path it is following, the front outside tire is turning in faster than the path it is following.

 

[RayH]

In normal 4X4 mode, both your front and rear axles have open differentials, this is the reason for one wheel on each axle spinning while the other does nothing. When you push the "lock" pedal, it mechanically locks the rear differential so their is no longer "differentiation" between the rear wheels. It acts as a solid axle shaft connecting the rear wheels. The front differential does not lock.
The binding while turning is normal in 4X4 whether you have locked the rear differential or not. The reason for the binding while you turn in 4X4 is because the front and rear axles are locked solidly together with each other. As you go around a turn, the rearend of the tractor takes a shorter path through the turn than the frontend does, so the front and rear tires are trying to turn the same speed as each other but are covering different distances. Every so often either a front (usually the front) or a rear tire will "scrub" or hop/skid/ slip, just alittle to make up for the difference in distance traveled between the front and rear tires. If you have the rear differential locked, the "scrubbing" is worse because now you have to deal with the different distance covered between the two rear tires as well.

 

[Mike_Lipke]

One, two, three,
All together now......

They all do that.

 

[Speedy7]

After using the tractor again this morning, I guess what I'm feeling is really mechanical feedback on the steering wheel when in 4WD mode. Given that I feel it when moving pretty slow, it's probably not related to rear/front binding, but probably related to the drive mechanism of the front axle/wheels. I have no idea how the front wheels is driven (no obvious drive shaft, perhaps hydraulically?), but I am just trying to determine if that kind of mechanical feedback on the steering wheel is normal in 4wd mode?

 

[HomeBrew2]

You know, you may be feeling the "paddle" effect of the ag tires. I park my BX on my concrete patio (I live alone /forums/images/graemlins/wink.gif And with the ag tires on hard surface, it will ... kindof ... undulate when crawling on the concrete due to the tire ribs.
The front drive shaft is enclosed in a kindof plastic tube/shroud thing.
Cheers!

 

[RonR]

I can feel when my BX2200 is in 4WD by the way the steering feels when I am turning with no load on the BX. Can't describe it, but it feels different. 2WD will be much easier on the turf. If you take the MMM off, crawl under there and you will see the drive train. Also notice all the "delicate" parts exposed without the MMM. Be careful or buy/build a skid plate.......... I'm making one over the winter.

The 4WD is mechanical and I'm sure it has a differential. As has been stated here earlier, the diff lock only locks the rear wheels.

Hope this helps.
ron

 

[MadReferee]

</font><font color="blue" class="small">( I have no idea how the front wheels is driven (no obvious drive shaft, perhaps hydraulically?), )</font>

On the B series, and probably the BX series also, there is a drive shaft (Kubota calls it a propeller shaft) that goes from the transmission to a differential bevel gear at the center of the front axle. There is a great diagram of the internal parts in the WorkShop Manual.

 

[sonofczechgun]

I know what you mean. My Jeep feels the same, I can tell when the front wheel hubs are locked just by the feeling in the steering wheel.
And now, when I started to drive a tractor too, I feel the 4x4 there also.

 

[btolle]

One more factor to add to the equation is that your tires are not manufactured the same standards as auto tires. They are probably a little out of round to start with.

When I ride my B7510 to the service station to get fuel I can see the rear tires "wobbling" back and forth.

Tractor tires are not balanced and at least on both Kubota's I have owned the way the wheel hubs are mounted to the axles the hubs may have a small amount of "wobble" in them. With a top speed of 10 MPH it's not that critical.

You do not have any suspension on a tractor either, no springs and shocks to dampen the wheel movement. The only way to change the ride quality on a tractor is to run more or less air pressure. When I picked up the B7510 the dealer had 44# of air in all of the tires and it nearly beat me to death on the 3 mile ride home. I dropped the pressure to about 25 in the rear and 20 in the front and it rides lots better and has better traction. They got that 44# idea because that is the maximum air pressure shown on the tire sidewalls.

But, I also own a Jeep Rubicon with mud tires on it so I am not used to a very smooth ride!

Bill Tolle

 

[Speedy7]

I just received my shop manual today, and got to see the front drive mechanism. A bunch of bevel drive gears, including one on the axle pinion. I think what I'm feeling in the steering is just NVH associated with all the front gears that are activated when in 4WD mode. It's very noticeable from 2WD mode, and I guess I just have to live with it.