T740 Shuts down

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ecbello

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Joined
Jun 13, 2024
Messages
7
Engine shuts down and unit comes to an abrupt stop while turning right.
Never does it to the left, forward, reverse, lift or lowering.
It has good fuel and replaced fuel filter. Replaced fan and main hydraulic filter. Drained and refilled hydraulic oil.
No error codes.
I can start the unit up immediately after it shuts down and operate the unit for almost 5-20 minutes before it acts up again.
It almost feel to me like the pump is locking up by building pressure and stopping the engine. All lights stays on when engine stops. Does not seem like its an electrical issue.
Machine functions perfectly other than this issue.
Should I be looking for a sticking or a relief valve issue?
Any suggestions?
 

Equipment_Tech

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Jun 16, 2023
Messages
98
Your stall guard is supposed to stop the engine from shutting down when under extreme load

What is your hydraulic level at ?
 
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ecbello

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Jun 13, 2024
Messages
7
Hi,
My hydraulic level is within spec. It's in the middle of the level sight glass. Like I mentioned, we drained the tank, refilled with fresh fluid and replaced the filter.
This issue was happening before we changed the fluid. The unit came in because it was losing power to travel and lift/lower. We found that the belt tensioner on the belt was not tight enough and the pump pulley was slipping. We tightened the tensioner and it fixed that issue.

When the unit shuts down, its never under extreme load.
 

Equipment_Tech

Well-known member
Joined
Jun 16, 2023
Messages
98
Hi,
My hydraulic level is within spec. It's in the middle of the level sight glass. Like I mentioned, we drained the tank, refilled with fresh fluid and replaced the filter.
This issue was happening before we changed the fluid. The unit came in because it was losing power to travel and lift/lower. We found that the belt tensioner on the belt was not tight enough and the pump pulley was slipping. We tightened the tensioner and it fixed that issue.

When the unit shuts down, its never under extreme load.
Lol....

Clearly the machine cannot be under any load if its shuts down,

The "extreme" load shuts it down

Just to clarify, you said......

Engine shuts down and unit comes to an abrupt stop while turning right.

well.....
Depending on how hard your working the machine
(rpms - time - atmospheric temperature - ect)

It may not be an extreme load but it is still a load, skid steers are not light weight

If your stall guard was bypassing or not working properly it could stall the engine out.
 
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ecbello

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Jun 13, 2024
Messages
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What I meant to say is that the machine is not lifting a load or at least it has not happened when I'm moving dirt or picking up a load with the grapple. It also can shuts down while doing a slow right turn and RPM up.

Yes, it comes to an abrupt stop. Almost as if you hit an emergency stop button that stops the engine and the machine on a dime! I also noticed that it happens more when the rabbit switch is above half way, rpm is up and I start moving the joystick around 1 and 2 o'clock.

Can you explain this stall guard and location? I can't seem to find any information on google on a stall guard on Bobcats.
Is this stall guard part of the hydraulic pump?
 

Equipment_Tech

Well-known member
Joined
Jun 16, 2023
Messages
98
I understand what you mean just remember any movement of the machine is a load

First thing you need to figure out before trying to replace or locate the stall guard is what is causing the extreme load.....

The extreme load can damage the stall guard as said before

I would start by swapping out the pressure relief valves for the drive motor. (Right - Left)
 

Equipment_Tech

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Joined
Jun 16, 2023
Messages
98
What I meant to say is that the machine is not lifting a load or at least it has not happened when I'm moving dirt or picking up a load with the grapple. It also can shuts down while doing a slow right turn and RPM up.

Yes, it comes to an abrupt stop. Almost as if you hit an emergency stop button that stops the engine and the machine on a dime! I also noticed that it happens more when the rabbit switch is above half way, rpm is up and I start moving the joystick around 1 and 2 o'clock.

Can you explain this stall guard and location? I can't seem to find any information on google on a stall guard on Bobcats.
Is this stall guard part of the hydraulic pump?
Yes, the stall guard is part of the hydraulic system.
 

Equipment_Tech

Well-known member
Joined
Jun 16, 2023
Messages
98
I understand what you mean just remember any movement of the machine is a load

First thing you need to figure out before trying to replace or locate the stall guard is what is causing the extreme load.....

The extreme load can damage the stall guard as said before

I would start by swapping out the pressure relief valves for the drive motor. (Right - Left)
After swapping the relief valves, the problem will switch sides providing that is the issue.

It could be a seal inside the drive motor itself but you have to start with the basics first
 
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ecbello

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Jun 13, 2024
Messages
7
Now I completely understand what you mean about any movement is a load. I'm not new to the mechanical field, but I am new to the construction machine field and learning more about these machines because I have customers that prefer for me to maintain and repair them. My primary business is in the repairs of all type of forklifts, mechanical and electric. But as you know, everyday is something new and a challenge.

If you notice on my opening comment, I pointed to the relief valves, but I did not want go any further until I spoke to someone like you who can explain it to me better, and having a second opinion is better.
I feel that the system is creating a hydro lock when the issue occurs, but not sure which valve is the culprit. I wouldn't think its a seal, because then it would be constant, and the issue almost feel like its intermittent.
I will start with swapping the relief valve and keep you updated. I thank you for taking your time to help.
 
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ecbello

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Jun 13, 2024
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I removed both front solenoids from the front of the pump and swapped. Tested and same issue.

I removed both rear solenoids from the back of the pump and swapped. Tested and same issue.

I put the unit on stands, and tested unit with tracks off the ground the problem did not happen.
Put it back on the ground and tested, the problem occurred again moving the joystick at 1 and 2 o'clock position.

I'm stumped!
 

Equipment_Tech

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Joined
Jun 16, 2023
Messages
98
I removed both front solenoids from the front of the pump and swapped. Tested and same issue.

I removed both rear solenoids from the back of the pump and swapped. Tested and same issue.

I put the unit on stands, and tested unit with tracks off the ground the problem did not happen.
Put it back on the ground and tested, the problem occurred again moving the joystick at 1 and 2 o'clock position.

I'm stumped!
Well since your having issues finding the relief valves maybe you should try draining the oil from your drive motor to see if there are any metal shaving in the oil. 80-90 gear oil.

Also note. When removing the plug there should not be much pressure, if oil flys out as removing the drain plug that means your seal inside the motor has failed
 
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ecbello

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Jun 13, 2024
Messages
7
Hi,

Customer picked up the unit and will use the unit for a necessary job with the issue. He will return it once the job is over so that I can continue to diagnose.
Once its back I will follow your advice and keep you informed.
 
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