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Old 08-04-2018, 09:57 PM
Maine Maine is offline
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Default Transmission: X1120 vs X900/X1100/X1140

I noticed a difference between the transmissions on the X1120 and on the X900, X1100 and X1140. The cylinder at the top rear of the transmission housing on the X1120 is a different shape and has an external pipe connected to the end of it. I first saw the difference at the local dealer, and confirmed it in the parts listings. The parts diagrams show a different internal configuration. The X1120 unit appears to be simply a piston in a cylinder while the X900, X1100 and X1140 units appear to have several springs acting on a piston in a cylinder. In both cases the piston appears to act on the swash plate.

I think I've figured out the reason for the difference. The top speed for the X1120 is rated at 29 mph while the X900, X1100 and X1140 are rated at 25 mph. Inside the cylinder at the rear of the transmission is the piston which controls the swash plate of the hydraulic motor which powers the wheels. The motor swash plate position along with the pump swash plate position determines the output speed of the transmission. It appears, based on the parts listings, that the motor other than the control piston, pump, regulator and charge pump are identical for all the X models. Also identical are the transmission gears and the ring and pinion in the rear axle. So my guess is the difference in the motor control piston of the X1120 is to enable the higher top speed.
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File Type: jpg 20180804_185231-1.jpg (19.8 KB, 65 views)
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Old 08-04-2018, 10:24 PM
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my x1100c will do 30 on a real good hard surface unloaded. i think the main difference in speed on the x1120 is because it is considerably lighter than the x1100. i also think the difference you notice is to make the transmission in the heavier machine a little more aggressive. so in theory if you converted an x1120 over to the x1100 you may go faster but i really doubt it that it would make that much difference. but if you converted the x1120 and put much larger tires and wheels on it maybe the extra torque would make the power to the tranny carry the extra ratio and go faster
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Old 08-04-2018, 11:13 PM
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The X900 has the same motor control piston as the much heavier X1100 and X1140 so I don't think the difference in the motor control piston between the X1120 and the other three models is due to weight alone.

The X1120 has a higher power to weight ration than the X900, X1100 and X1140. My thought is the difference in motor control piston system helps in taking advantage of that difference in power to weight ratio.
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Old 08-05-2018, 07:20 AM
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Quote:
Originally Posted by Maine View Post
The X900 has the same motor control piston as the much heavier X1100 and X1140 so I don't think the difference in the motor control piston between the X1120 and the other three models is due to weight alone.

The X1120 has a higher power to weight ration than the X900, X1100 and X1140. My thought is the difference in motor control piston system helps in taking advantage of that difference in power to weight ratio.
you may very well be right. is the different plumbing on the x1120 a case pressure bleed?
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Old 08-05-2018, 08:12 AM
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The added plumbing on the X1120 is part of a fundamentally different system for controlling the motor swash plate. The motor control piston system in the X1120 has a larger diameter piston which appears to be actuated by fluid from the external hydraulic line. There are no springs in the system.

In contrast the X900/X1100X1140 system has two springs which push on a smaller diameter piston, and there is no obvious (from the parts diagrams) path for hydraulic fluid to push against the piston. The "piston" may serve only to transfer the spring force to the swash plate.

Attached are images from the parts listings of the X1120 piston and hydraulic line, and of the X900/1100/1140 piston.
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File Type: jpg X1120 Piston.jpg (18.4 KB, 54 views)
File Type: jpg X1120 Pipe.jpg (20.2 KB, 53 views)
File Type: jpg X1100 Piston.jpg (19.4 KB, 54 views)
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Old 08-05-2018, 08:26 AM
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i will admit that i am unsure why K made these changes and i am more familiar with the servo system on the older machines,but i am sure that the newer X models still use a servo system to control the swash plate and there are tiny oil passages that bleed operating pressure back to the case in order to allow the servo to hold the swash plate in position. find a diagram of oil flow and it will make some sense. in short your foot controls a valve that diverts oil to a servo that in turn operates the swash plate.
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Old 08-05-2018, 08:50 AM
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Quote:
Originally Posted by aurthuritis View Post
i will admit that i am unsure why K made these changes and i am more familiar with the servo system on the older machines,but i am sure that the newer X models still use a servo system to control the swash plate and there are tiny oil passages that bleed operating pressure back to the case in order to allow the servo to hold the swash plate in position. find a diagram of oil flow and it will make some sense. in short your foot controls a valve that diverts oil to a servo that in turn operates the swash plate.
There are two swash plates. One for the pump and the other for the motor. My guess is you are referring to control of the pump swash plate, not the motor swash plate.

The parts I illustrated above control the motor swash plate and are not involved with the pump swash plate. I don't see any evidence of any hydraulic passages which would supply pressure to the piston in the X900/X1100/X1140 motor swash plate piston, and don't see any room for internal passages in the piston housing.
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Old 08-05-2018, 08:51 AM
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The (non-X) 900/1100/1140 motor swash plate control also used two springs, though in a different housing.

Last edited by Maine; 08-05-2018 at 09:29 AM.
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Old 08-05-2018, 08:55 AM
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yea the springs were there to hold the servo control in neutral. in order to fully understand this i need to see the oil flow diagram
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Old 08-05-2018, 09:30 AM
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Quote:
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yea the springs were there to hold the servo control in neutral. in order to fully understand this i need to see the oil flow diagram
Which springs and which "servo control" are you talking about? Are the springs external or internal?


I'm talking about springs and the control for the motor swash plate which are inside the rear piston housing, not the overall servo control system.
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Old 08-05-2018, 11:39 AM
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on the x1100c under the cap is the control piston 1 that returns the swash plate motor to it's neutral position when control piston under pressure from hydraulic control circuit is lowered. on the x1120 this action in applied via case dump pressure against a servo piston. "i think" instead of springs.
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Old 08-05-2018, 12:03 PM
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i think i can explain the difference but put very simply so it leaves out many details. when the control piston actuates the swash plate motor it has to overcome the spring pressure and this action raises the control circuit pressure and is diverted to a charge pressure on the pump internal without raising case charge pressure. now something i am unsure about is did K use a spring system to raise the pressure or lower it. on the x1120 the case charge pressure"i think" acts against the control piston 1 and if it has more force than the spring system could actually cause the charge pressure to be higher.
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Old 08-14-2018, 02:27 PM
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My copy of the Worshop Manual (WSM) for the X900 and X1120 arrived, and I went through the section on transmission operation including the fluid flow diagrams.

The only difference in the layout or operation of the transmissions, other than some pressures, is "Control Piston 2" which is inside the cylindrical housing at the top rear of the transmission. This is the part I discussed in the initial post in this thread. Control Piston 2 works on the HST motor swash plate and tries to move the swash plate towards the neutral position, countering the action of Control Piston 1.

Control Piston 2 in the X900 has two springs which provide the force and is not connected to a hydraulic circuit. Control Piston 2 in the X1120 is larger diameter and is actuated by a connection to the charge fluid circuit which also supplies fluid to the intake of the HST pump and to the Servo piston which actuates the pump swash plate. Control Piston 2 does not have any springs.

In both the X900 and X1120 transmissions Control Piston 1 is connected to the fluid circuit between the HST pump discharge and the HST motor intake.

The X900 HST motor swash plate position is affected only by the pressure of the fluid between the HST pump discharge and HST motor intake which acts on Control Piston 1. Increased pressure between the HST pump discharge and th HST motore results in higher displacement of the HST motor, which in turn means slower speed and higher torque for the transmission output shaft.

The X1120 motor swash plate position is affected by both the pressure of the fluid between the HST pump discharge and HST motor intake which acts on Control Piston 1, with increased pressure resulting in higher displacement of the motor; and the pressure of the charge fluid circuit which acts on Control Piston 2, with increased pressure resulting in lower displacement of the HST motor. Transmission output shaft torque increases and speed decreases as the motor displacement increases.

The charge fluid is pressurized by the Charge Pump, which is driven by engine via the transmission input shaft. The discharge from the pump supplies fluid to the HST pump as well as the Servo Piston and Control Piston 2 in the X1120. It is not obvious how the pressure of the charge fluid varies with engine speed and pump swash plate setting. The maximum pressure is regulated by the Charge Relief Valve but it is not obvious when that valve is open. When the HST pump swashplate is in neutral the pressure is probably at the charge relief valve setting. However once the HST pump swashplate moves from neutral and the fluid flows into the HST pump the pressure will tend to drop.
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