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I have a Bobcat 943. Left side travel is very weak. It does…

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I have a Bobcat 943...
I have a Bobcat 943. Left side travel is very weak. It does work though. Condition worsens as oil heats up. If I lock the brake and try to travel the pump does squall (I assume the high press relief opens). However nothing like the other side will. (Left side power and squalling muted when brake is set as compared to the right side). I pulled the high press relief and charge relief to check for trash stuck in the system to no avail. Hyd filters replaced. Belt and tension correct. I have seen another post about checking the charge pressure and I am considering this but this happened suddenly and I question whether a weakened spring relief would create this condition so abruptly. I am considering swapping the 2 travel motors to see if the problem moves with the motor. But I would rather not if I don't have to. I don't know if it is worth noting that the charge relief did not have any spacers installed and all other hyd work normally.
Submitted: 8 years ago.Category: Construction and Road Equipment
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Answered in 23 hours by:
10/29/2014
Mechanic: Dan, Technician replied 8 years ago
Dan
Dan, Technician
Category: Construction and Road Equipment
Satisfied Customers: 15,102
Experience: 17+ yrs. shop and field experience with all major brands of heavy equipment and trucks - 1995 WyoTech graduate.
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Hi my name is***** will try to help. It sounds like you might have a drive motor problem. To confirm this verify your pressures to the drives are in OEM spec to both drives. Check inside your filter for metal/debris that would indicate a drive motor or component failure occurring. If found then disconnect the drive motor case drain hose into a bucket and with the machine pushing against a loading dock etc to prevent movement, engage travel. Oil should not come out under high volume or pressure. It should be a low volume trickle of oil. compare left and right sides. If one comes out at a high pressure or volume that drive motor is bad.. Let me know if you need further help.
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Mechanic: Dan, Technician replied 8 years ago
Hi, I just wanted to follow up with you to see how you made out with this or if you had a chance to do the checks. Let me know and if you need further help I will do what I can to help.
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Customer reply replied 8 years ago
There are no test ports on this machine to check pressures. Doing this is cost prohibitive at this point (#16 hoses with flat seal fittings = mucho dinero). I swapped the left and right drive motors. The problem did not move. Still on the left side. I am on a shoestring budget and don't have a lot of money to throw at this. Don't see anything unusual from the hydraulic filters.
Customer reply replied 8 years ago
I suspect something in the hydraulic pump. This is where I previously checked the high press relief for debris and also the charge relief for debris. None found. The charge press should be 400 lbs. This is adjustable buy adding or subtracting washers. Currently there are no washers in this relief.From what I gather, I would have to remove the entire engine with hydraulic pump assy to properly disassemble the pump. I'm trying to avoid this.
Mechanic: Dan, Technician replied 8 years ago
Thanks for the update. There are pressure test locations on your machine but there are plugs that have to be removed and test fittings/adapters installed to install your gauges. I think the best next step is to get you the service manual so you have all the troubleshooting steps,schematics, and specs, for this machine. Copy and paste this link in your browser for the complete shop manual for under 10 dollars in PDF format.
http://instantmanual.net/bobcat-943-skid-steer-loader-service-repair-manual.html?ap_id=bobcatmanualpdf
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Mechanic: Dan, Technician replied 8 years ago
Hi, I wanted to follow up with you and see how you are making out on this? Was the information I provided helpful? do you still need more help?
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Customer reply replied 8 years ago
I already have the service manual. This manual has one test location to check the charge pressure. My understanding is that the charge pump supplies press to both of the hydrostatic pumps, therefore if the left pump is operating properly, the supply press should be ok. I know there can be a fine line with pressures. Is it worthwhile checking this pressure anyway? This pump is the first pump in line with the other pumps, therefore is it safe to assume the splined or geared connectors are ok?
Mechanic: Dan, Technician replied 8 years ago
Thanks for the update. You have two main pumps and the charge pump on the end of the assembly. Your functions are split between the two main pumps and your charge pump is your control pressure that signals each pump. You should check your pressures to see if the charge pressure is in spec and to see what the main output pressure is to each drive to see if you have a control valve problem causing low pressure to that one side or if the problem is in fact in one of the two main pumps. Usually one pump controls your implements /work equipment and the other one for travel but in some cases I have seen right and left travel coming from separate pumps. Follow the lines from left and right travel to confirm if it is running off one pump or split between the two. They are variable displacement pumps and one pump may not be reaching full stroke for full volume of flow. I have also seen the drive couplings fail that drive the pumps but would be unlikely if all other functions are strong and they still work. If it is only that left side and it is not the drive then it has to be either a pump problem or in the control valve.
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Customer reply replied 8 years ago
Each pump is dedicated to a drive motor. I'm sorry, I thought you were familiar with this set up. (Two hydrostatic pumps that drive two drive motors, independently). If the charge pump press feeds both hydrostatic pumps at the same time, wouldn't both hydrostatic pumps be inadequate to drive the motors if the charge press was too low? As far as the drive coupling go, this is the first pump in a row of four (engine to hydrostatic pump, hydrostatic pump, charge pump, hydraulic pump) in that order. So if the coupling were bad, all functions would be slow. They are not. Everything functions normally but the left drive. No easy way to test hydraulic press coming out of the hydrostatic pump as I mentioned before.
Mechanic: Dan, Technician replied 8 years ago
I do know how the pumps are coupled and how the charge pump is at the end. I was only unsure without looking it up how the functions were split between the pumps. Your implements are also split between the pumps. Now there should be what is called cycle times in your manual for the track speed, boom raise and lower, bucket curl and dump, etc. Since I do not have the manual for this machine I can not say which functions are designated to which pump but they are divided. If you have good pilot pressure from the pilot pump which signals the main pumps to stroke and one of the two pumps is not stroking as is should despite the pilot signal pressure being there, then that pump has either a control problem or another problem internally. The sure way to verify this is to flow test the pumps which I know is not possible in this case. But this is why I suggested checking the signal pressure for both pumps because which pump is signaled to full stroke depends on what functions you are operating. Even though they are bolted together, one can have a problem. The one would be the one that drives the LH side. I did not know without seeing the manual or machine which pump.... front or rear was for the left side and also what other functions that one controls. If your manual covers that and gives cycle times, you can check the cycle times for those other functions.This will help narrow things down to a potential pump problem
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Mechanic: Dan, Technician replied 8 years ago
Hi, How are things progressing with this? I wanted to follow up with you to see where you are with this or if you needed further help? Are you happy with the information I have given so far?
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Dan
Dan, Technician
Category: Construction and Road Equipment
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Experience: 17+ yrs. shop and field experience with all major brands of heavy equipment and trucks - 1995 WyoTech graduate.

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