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Link belt 2700C series II Hydraulic IssuesA short at the…

Link belt 2700C series II...
Link belt 2700C series II Hydraulic Issues
A short at the split bolt connector in the console has fried the circuit boards in the control panel, so I've converted the machine to manual controls and throttle.
Every time we operate the right track, boom and bucket, the engine smokes, pulls down and can be killed with the hydraulics. My understanding is that all three of these operate off of one pump. Why would all three pull down and the other pump (left track, swing and stick) works just fine?
I"ve got the service manual and studied the schematics, I"m at a loss
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Answered in 32 minutes by:
11/24/2013
Mechanic: Dan, Technician replied 8 years ago
Dan
Dan, Technician
Category: Construction and Road Equipment
Satisfied Customers: 14,846
Experience: 17+ yrs. shop and field experience with all major brands of heavy equipment and trucks - 1995 WyoTech graduate.
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Dan :

Hi my name isXXXXX will try to help. Your functions are split between two pumps and there are signal lines to the servos that receive pilot pressure when a function is operated to stroke the pump. When running multiple functions at once, your pumps both should be stroked for two pump flow. It sounds like one of the pumps is not stroking as it should. Check your pressure to the small signal lines for each pump when the functions are operated to see if this is the case. Verify that there is no metal/debris in your in tank return filter indicating a pump or component problem occurring. If ok then even though it is recommended to have all electronics functioning for the machine to operate most efficiently you could potentially tee both signal lines together so both pumps are stroked when a function is operated as long as there is no problem with one pump. Let me know

Dan :

I also recommend pulling your relief cartridges and inspecting them for debris and damaged o rings that could cause a loss of pressure in your functions if pressure is bypassing.

Customer:

Pilot pressure is provided by a third (pilot) pump that runs pressure thru the hand controls and to the main control valve. That then moves valves to apply full pressure to either side of the cylinder or track drive motor. The hydraulic schematic seems to keep the two pumps on seperate circuits until they hit a common return line to the radiator (hydraulic cooler), filter and relief valve. If the problem is on one side of the hydraulics (right track, boom and bucket), what kind of problem would effect all three at the same time and not one specifically?

Customer:

Link belt is the same as Case except for the isuzu motor (and the paint of course). My case dealer isn't much help :(

Dan :

JCB is also the same as well. They are all manufactured by Summitomo

Dan :

Check your pilot strainer for metal/debris. It should be a small aluminum canister with an element inside located in the pump compartment

Dan :

verify your pilot pressure. I do not have the exact spec in front of me but you should see around 550-600PSI range

Dan :

The signal pressure to signal the pump is from pilot pressure( pilot pump) This signal comes from the control valve with a signal line to the pump. You will see a couple small signal pressure lines to your pump

Dan :

Tee in with a gage on both lines and verify your pressures there

Dan :

if you have good signal pressure then your problem could be internal with one pump. You could always try to swap the lines at the pump to see if the problem switches with the other functions

Dan :

Even if you have to adapt/make a test hose if there is not enough slack then it will be worth it

Dan :

first verify the signal pressure on both pumps using a 1000PSI gage

Dan :

if a signal pressure problem then go back to the main control valve

Dan
Dan, Technician
Category: Construction and Road Equipment
Satisfied Customers: 14,846
Experience: 17+ yrs. shop and field experience with all major brands of heavy equipment and trucks - 1995 WyoTech graduate.
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Mechanic: Dan, Technician replied 8 years ago

Hi, I just wanted to follow up with you to see if you still needed help. If you still need help please reply back and Ill be glad to assist you further and if you are satisfied with the information I have provided please rate Ok to excellent or accept as it is how I get credited for helping you or reply back for more information. Let me know.

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Customer reply replied 8 years ago

Sorry it took me some time putting the wrenches to the excavator. Hope you had a good Thanksgiving also. I did a complete hydraulic filter//strainer change to no avail. I decided to switch the two main hydraulic pump lines as you suggested. Excavator did NOT exhibit the problem at all, the only noticable difference being a slower operating bucket. I decided to switch the lines back and the problem seems to be GONE. I piddled around for about 30 minutes and excavator seems to operate fine. No idea if a piece of dirt dislodged or what happened, but I'll take the fix! Better lucky than good lol. THANKS!

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Dan
Dan, Technician
Category: Construction and Road Equipment
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