cold 743 wanted to jump forward on start attempt

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marko13

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Apr 29, 2023
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102
Yesterday I almost freaked out when my trusty 743 started to act weird for first time. It's been cold here for a bit. It sat for at most a week or two since moving from one spot to another. I gave the glows 60sec and tried to start and both drive levers lurched forward and it died. tried several times with glow in between hoping something would warm up or get unstuck. I had a "must do now" task for it so I was worried.
finally after several attempts it started normally without the sticks flying forward and grinding. It then ran and operated normally.
I'm guessing oil was thick or some lever was frozen in a wrong position????
any thoughts on what it could have been and what I should be looking to address when it warms up?
Thanks
 

Chris 8603

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Aug 4, 2023
Messages
114
When you fiqure it out please let me know!!! I've had mine now for 6yrs and it has done since the day I got it. I've changed the hydro fluid and filters, rebuilt the controls everything but rebuilding the pumps. If it's close to 32° or less it does the same thing. But mine only will do it when the parking brake is on. Which makes no sense being the two are in no ways connected. As long as the parking brake is off, it will work just fine no matter how cold it is. I've talked to several bobcat techs and other repair shops and nobody has any idea. So ????
never seen this be curious what others think
 

laurencen

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Oct 3, 2016
Messages
215
all I could rhink of is the centering blocks are not set right and levers are centering on the springs, when warm easier to move than sub zero temps
usually the btake left on will cause the pressure to increase due to wheel creep
 
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Chris 8603

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Aug 4, 2023
Messages
114
I have no idea!! I've reset it by the book 3 times, and even took all of it off and left nothing but the valve levers. It still did it. So I'm not sure what causes it. It's always forward on mine also. And I can feel a forward pull on the sticks when it does it. Luke Marko13 says, only when it's cold. Oh and I tried a lighter oil one time since I was going to flush the system anyway. So if anyone fiqures it out, please let us know.
 

mikelv

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Sep 9, 2023
Messages
50
I have a similar issue on my case 1830, its also only when very cold. mine will even drag the starter if I don't center the levers. I figured its a centering adjustment but it's something I haven't gotten to yet. (had it less than a year) I did notice when replacing the drive chain (chain removed) that the drive motor would spin at idle no matter what the position of the drive levers. The 1830 doesn't have a drive lockout so the pump and drive is always active. Good luck, I hope you get it figured out.
 

Topper1

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Feb 19, 2023
Messages
53
Theres a lot going on internally with a hydrostst pump. But to put it simply,
When cold, oil does not flow as intended.
The actuator valve is spring centered but is also internally pressure regulated.
The initial startup oil pressure spike pushes the swash plate servo actuators, easily overcoming the spring centering (usually fwd).
After a few seconds of running, the internal pump charge pressures equalize to normal, and the symptom vanishes.
It was a common issue with a lot of the early rexroth & danfoss hydrostat pumps, especially those with hydraulic pilot hand controls. Some early linkage controlled machines also experienced this oddity.
 

Chris 8603

Well-known member
Joined
Aug 4, 2023
Messages
114
Theres a lot going on internally with a hydrostst pump. But to put it simply,
When cold, oil does not flow as intended.
The actuator valve is spring centered but is also internally pressure regulated.
The initial startup oil pressure spike pushes the swash plate servo actuators, easily overcoming the spring centering (usually fwd).
After a few seconds of running, the internal pump charge pressures equalize to normal, and the symptom vanishes.
It was a common issue with a lot of the early rexroth & danfoss hydrostat pumps, especially those with hydraulic pilot hand controls. Some early linkage controlled machines also experienced this oddity.
That's good to know, thanks for the info topper1. Mine usually last doing it about 10-15 before it will idle normally
 
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marko13

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Apr 29, 2023
Messages
102
mine has no parking brake. haven't opened it up to see why but have seen the utube on likely cause (frozen brass 'pistons')

mine is also back to creeping when running after having fixed it when I first got it last summer.

but never before that weird action on trying to start.

i guess i'm glad to know i'm not the only one :)
 

dfb

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Joined
Sep 11, 2017
Messages
98
Mine just required adjustment when i got it and I would consider it essential. It will cause the levers to buck when applied and is strong enough to keep the machine from moving.
 
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marko13

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Joined
Apr 29, 2023
Messages
102
what part required adjustment? mine does buck sometimes but i chalked that up to operator error
 

HmsNimrod

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Joined
May 17, 2022
Messages
20
I think it's a creep issue I hold my sticks back a bit to start until it warms U and I can make necessary adjustments, also I have to take off the E-brake when starting to avoid the bad grinding sound. All issues seem to be due to needed adjustments on my machine. Glow plugs have nothing to do with Lerch.
 
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