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Discussion Starter · #1 ·
I have had a John Deere X729 for a year. It has worn the grass bare in a circle around my trees. The circle is caused by the tire(s) on the outside of the radius (i.e. the right tire(s) since I cut with the left side next to the trees).

I have noticed the front tires actually move slightly sideways (to the left) when going in a circle. It would take a lot of force to move the front of the tractor sideways and, apparently, one or more of the right tires is generating this force at the expense of the grass.

The original salesman made a special point that the four wheel drive tractors do not have this problem (unlike the tractors that have four wheel steer only). The dealer has driven the tractor and claims there is nothing wrong with it. My lawn claims otherwise.

Is my tractor the only one doing this? Does anyone have insights/suggestions for solving this problem?
 

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I have had a John Deere X729 for a year. It has worn the grass bare in a circle around my trees. The circle is caused by the tire(s) on the outside of the radius (i.e. the right tire(s) since I cut with the left side next to the trees).

I have noticed the front tires actually move slightly sideways (to the left) when going in a circle. It would take a lot of force to move the front of the tractor sideways and, apparently, one or more of the right tires is generating this force at the expense of the grass.

The original salesman made a special point that the four wheel drive tractors do not have this problem (unlike the tractors that have four wheel steer only). The dealer has driven the tractor and claims there is nothing wrong with it. My lawn claims otherwise.

Is my tractor the only one doing this? Does anyone have insights/suggestions for solving this problem?
Welcome to the forum! :Welcome1: I really don't have a lot of experience with these tractors, but know my 2210 will do the same -- especially if edging around something combined with a slope. My solution was to widen the mulch beds surrounding trees etc and the problem went away. These tractors will turn a lot sharper than is really practical. Other than that, how do you like your X729? :)
 

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I'm sorry to say it, but your dealer is full of it. My X729 cuts circles just as bad as any two wheel steer tractor. The aggressive pattern of the tire doesn't help matters either. I upgraded to the X729 from an X475 AWS, which pretty much did the same thing too. My advice, is to learn how not to turn sharp around areas like this. I either make an extra pass to hit these areas in a striaght line, or I will make a three point turn out of it. It is more of a problem when the ground is wet, than dry.
 

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Discussion Starter · #9 ·
Welcome to the forum! :Welcome1: I really don't have a lot of experience with these tractors, but know my 2210 will do the same -- especially if edging around something combined with a slope. My solution was to widen the mulch beds surrounding trees etc and the problem went away. These tractors will turn a lot sharper than is really practical. Other than that, how do you like your X729? :)
Previously had a JD 265. It was the perfect lawn machine. I mow about 1 acre with hills. Also use the tractor to mow about 4 acres of horse pasture once or twice a year. Then there is snow blowing around the house and down the lane which is 1 block long. Bought the X729 to speed up the process, to get closer to the trees, and for the power steering. The wider deck speeds up the process, but it has been hard to get it leveled good enough to avoid an uneven cut between passes. It's passable. My old shoulders like the power steering. The tractor gets closer to the trees, but you know the rest of the story.
 

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Discussion Starter · #10 ·
The salesman said the rings were a problem with other AWS tractors, but this "new" system with 4WD solved that problem. I did not have the problem with my previous JD 265 which had neither 4WD nor AWS.
 

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I do not think there is anything wrong with the tractor. I have had the same issue with every tractor I ever owned.


I think it is consistent abuse to the grass in the exact same place repeatedly. I have a tree on a slight slope I will use as an example. The circle of 'no grass' is much more pronounced on the down side of the tree. WHy? The weight and force on that outside wheel with gravity and turning a 1000# tractor that wants to go straight (remember physics aply to tractor as well LOL) simple compacts the soil and the tread tears out the grass.

I tried replanting, but the only thing that works is to change mowing patterns.

That is my two cents.

Wether a 4wheel drive does this less than my 420 rear wheel will depend on differentials, if they are designed to be quick to send power to the outside wheels they will help the turn and hurt the grass less, if they are slow to move power they will be better for traction and get stuck much less but be harder on the grass in a tight turn. I have no experience mowing a lawn repeatedly with a four wheel drive to see the pattern.

So I change my pattern, ride the inside brake just before and through the turn to force the rear differential to put the power to the outside wheel and assist the turn and slow way down on these corners all to reduce the forces on the grass.

Yamadoo
 

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I have a number of areas where I turn as tight as it goes. My old 355D (2wd) and my 748 do not mess up the lawn. I don't go at real high speed when turning. Now the 749AWS might be a different animal in this respect.

When I got the 748 I had the HDAP removed and turfs put on.

If I were to put the 748 in 4WD it would tear the grass right off with the front wheels in a real tight turn. I have accidentally done that.

I was always a bit suspect about the full time 4WD being harder on the lawn than a 2wd although I have never tried one.

I have a few damp areas where the grass is thin and I have to be extra careful there. The ZTR I tried would tear up those areas with the caster wheels. The 748 does better there.
 

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AKA Moses Lawnagan
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I think it is consistent abuse to the grass in the exact same place repeatedly. I have a tree on a slight slope I will use as an example. The circle of 'no grass' is much more pronounced on the down side of the tree. WHy? The weight and force on that outside wheel with gravity and turning a 1000# tractor that wants to go straight (remember physics aply to tractor as well LOL) simple compacts the soil and the tread tears out the grass.

I tried replanting, but the only thing that works is to change mowing patterns.
I totally agree. My mother complained all the time about the guys who mowed her lawn wearing rings in the grass going around her trees. They used ZTR mowers. Since I started doing her yard (with a GT235 JD), it isn't as bad, but it is because I vary where I put the front outside wheel when I cuircle the trees, and I go very slowly. My X748 will cut rings in 2WD or 4WD if I don't go slowly.

It's a matter of retracing the same path in the grass every time, the speed that you make the circle, and the steering geometry of the tractor, and whether or not that outside front wheel is under power or freewheeling.

If you notice, when the front steering is at full lock, the outside tire has positive camber (top of the tire leans out). This makes the outside edge "dig in" at the bottom. Caster and camber are not adjustable on our GT's, it is a result of the angle of the wheel spindles on the axle and the axle's mounting to the frame. The relative caster and camber will change as the wheel goes from straight to lock in either direction, and is set as the best compromise through the full range of movement, because as the steering changes direction, it has to account for one wheel tracing a different arc than the other.

There is also the tendency for the rear wheels to "push" the front, which amplifies the outside front wheel's tendency to dig in, and slight differences in gear ratio and tire size make it worse when the front wheel is under power as in a 4WD. Some front tires are more rounded at the edges than others, they help reduce the scrubbing action, and the less aggressive the front tread is at the edges, the better (HDAP's are worse than standard turf tires).

The tighter the arc of the turn, the worse the effect. I made the mulched circles around my trees and my mother's about 6 feet diameter, which helped, and I just slow down when I circle my trees, and try to vary the track of the wheel when I can.
 

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Discussion Starter · #14 ·
I totally agree. My mother complained all the time about the guys who mowed her lawn wearing rings in the grass going around her trees. They used ZTR mowers. Since I started doing her yard (with a GT235 JD), it isn't as bad, but it is because I vary where I put the front outside wheel when I cuircle the trees, and I go very slowly. My X748 will cut rings in 2WD or 4WD if I don't go slowly.

It's a matter of retracing the same path in the grass every time, the speed that you make the circle, and the steering geometry of the tractor, and whether or not that outside front wheel is under power or freewheeling.

If you notice, when the front steering is at full lock, the outside tire has positive camber (top of the tire leans out). This makes the outside edge "dig in" at the bottom. Caster and camber are not adjustable on our GT's, it is a result of the angle of the wheel spindles on the axle and the axle's mounting to the frame. The relative caster and camber will change as the wheel goes from straight to lock in either direction, and is set as the best compromise through the full range of movement, because as the steering changes direction, it has to account for one wheel tracing a different arc than the other.

There is also the tendency for the rear wheels to "push" the front, which amplifies the outside front wheel's tendency to dig in, and slight differences in gear ratio and tire size make it worse when the front wheel is under power as in a 4WD. Some front tires are more rounded at the edges than others, they help reduce the scrubbing action, and the less aggressive the front tread is at the edges, the better (HDAP's are worse than standard turf tires).

The tighter the arc of the turn, the worse the effect. I made the mulched circles around my trees and my mother's about 6 feet diameter, which helped, and I just slow down when I circle my trees, and try to vary the track of the wheel when I can.
Thanks for taking the time to explain the physics of what may be going on. This is the kind of insight I am looking for.

As for abuse of the lawn by retracing the same track, I did not have the problem with my JD 265 except on steep hills.

Originally I blamed myself for going too fast (trying to take full advantage of the 4WS). Even a 4WS is subject to centrifugal force. Slowed to a creep; same problem.

As for one wheel tracing a different arc than the other: that's a good point. In other words: the outer wheel must go faster than the inner wheel. My understanding is the hydraulic system balances torque to each of the wheels. Therefore, to maintain torque on the outer wheel it would have to go faster. For example: when going up an uneven incline, if one of the front wheels rises off the ground (i.e. very low torque) it spins very fast. To compensate for this on the X729, JD provided a pedal to lock the wheels and make them all work even if one wheel is off the ground.

The above comments about equal torque to all wheels should also lead us to believe that no wheel should push another wheel. However, the evidence says this is probably happening.
 

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How does the 4WD work on the 7xx machines? I was on the JD web site last night picking out my "Future JD" and I think the next one will be one of the 7xxSE models (I do not want 4WS, just Diesel and 4WD) and it says it uses "Wheel Motors" in the front. Are the fronts hydro powered by separate hydro motors?
 

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My understanding is the hydraulic system balances torque to each of the wheels.
This is done by torque sensing in the hydraulic system. In order to do this the there has to be a bit of torque on the wheel. In 2WD the wheel is free wheeling. That is why I don't think the full time 4wd will ever be quite as good as 2wd. It may be close but not quite there.
 

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How does the 4WD work on the 7xx machines? I was on the JD web site last night picking out my "Future JD" and I think the next one will be one of the 7xxSE models (I do not want 4WS, just Diesel and 4WD) and it says it uses "Wheel Motors" in the front. Are the fronts hydro powered by separate hydro motors?
Prior to 2009 the 7xx 2 wheel steer models used a mechanical drive to the front. Much like the larger tractors. You have a lever to engage and disengage the 4WD. When it is disengaged the front wheels are free.

The new tractors use a full time 4WD where the hydraulic motors apply torque to the front wheels. There is a circuit that senses torque and tries to balance the wheels so there is no skidding. This technology was applied to the 748 from the 749.
 

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AKA Moses Lawnagan
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How does the 4WD work on the 7xx machines? I was on the JD web site last night picking out my "Future JD" and I think the next one will be one of the 7xxSE models (I do not want 4WS, just Diesel and 4WD) and it says it uses "Wheel Motors" in the front. Are the fronts hydro powered by separate hydro motors?
Starting with the '09 models, all the X7xx with 4WD use full-time 4WD, and the front wheels are driven individually with hydraulic motors; the HST pump provides the pressure to the front motors. This is the system which has been used for the 4WS/4WD, such as the X729/749. The '08 and earlier 2WS/4WD models (X728/748) use a part-time 4WD system with a mechanical front axle with a differential, and a driveshaft from the HST that can be engaged or disengaged as the operator desires, with a lever on the right fender next to the toolbox.

I don't know why JD changed this, unless to streamline production. I like my '08's part-time system, with the option to use 4WD only when you want or need it.
 

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Ok looks like when I am ready to shop I will be buying used then, I would rather have a part-time system with mechanical engagement.
 

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AKA Moses Lawnagan
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If you find a X748, or the model just before it (X59...whatever), jump on it. I absolutely love my X748SE, and I'm sure ccsial will agree, it's a tough mother. The diesel is worth the "price of admission". The seat alone is worth the SE's extra cost. I have some lower back problems, and I can go all day on the 748. My GT235 wears me out in a couple of hours. Just sitting here and thinking, I can't come up with anything I really don't like about the 748. I mowed my lawn, my rental lawn, my pasture, and a 'hired' yard, that's 8+ acres and change, on about 5 gallons of diesel.
 
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