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I have a 2004 bobcat skid steer, s250 turbo high flow, s/n…

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Ok, I have a...

Ok, I have a 2004 bobcat skid steer, s250 turbo high flow, s/n###-##-#### hyd. fluid foams up to the point of overflowing back out of the fill tube. I've replaced the hose from the hyd. tank to the pump, there were some questionable wear marks on it, I also replaced the o ring and seals on the right side drive motor. When operating the lift arms I can feel a jerky motion which would indicate air in the system. Other than operating the systems, is there a way to " bleed" the hyd. system of air? The other thing I'm leaning towards is the pump its self. Any recommodations? Thank You

Mechanic's Assistant: What is the complete model and serial number of your machine?

Model id S250 serial number###-##-####

Mechanic's Assistant: Is there anything else the Agriculture Mechanic should know before I connect you? Rest assured that they'll be able to help you.

This has started late last year and has gotten worse as the weather has gotten warmer. And yes it has bobcat hyd. oil as recommended. Any cost associated with inquiry?

Submitted: 1 year ago.Category: Construction and Road Equipment
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Answered in 11 hours by:
6/11/2021
Mechanic: Fieldtech59, Shop manager replied 1 year ago
Fieldtech59
Fieldtech59, Shop manager
Category: Construction and Road Equipment
Satisfied Customers: 202
Experience: Construction equipment repair technician since 1986, JLG certified, Shop manager since 2006.
Verified

Greetings, a number of things can cause foaming of hydraulic oil, but if your oil is good and clean, not contaminated, then the most common cause of foaming is ingress of air on the suction side of the pump. Once oil leaves the pump it's under pressure, there's no way air can enter the system on the pressure side of the pump and hydraulic system. I have seen Bobcat pumps crack, and those cracks can be dang near impossible to see. I've seen the case crack, I've seen cracks in the bolt threads where the four bolt flange suction adapter bolts to the pump. You mentioned you replaced the suction hose between reservoir and the pump, but be sure and check the hose that runs from the oil filter to the pump as well, that's a suction line as well. If you've recently worked on a drive motor that can enter air into the system. There's no simple method to bleed the air and Bobcat machines aren't a "return to tank" hydraulic system, rather, they use a loop system, returns back to the pump inlet, all the reservoir does is allow oil to move in and out of the system as cylinders are extended and retracted. It takes a good bit of time, but the only way to purge the air in the system is constant cycling of the loader arm cylinders and the bucket tilt cylinders while driving the machine as well. If this doesn't work the air out and you've checked/verified your suction lines, then I'd be look at the pump. BTW, the problem wouldn't be caused by the hydrostat drive pumps as they are under internal charge pressure, if you had a problem with them you'd have a leak. Let me know what you find.

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Customer reply replied 1 year ago
Went back and checked suction hoses from the filter. The short hose from the tee to the pump has some chaffing, going to replace it. Also going to replace the seals on top of the pump where the control levers connect. They are leaking. Then will run it to see if I can work the air out of the system. Thank You for the help. Bob Broughton, MEM,. NYSDOT, Binghamton, NYNo thanks. I'm leaving in an hour and won't be back until Tuesday.
Mechanic: Fieldtech59, Shop manager replied 1 year ago

No problem, I'm glad to help. BTW, if you're pump has a 4 bolt flange connections to the suction side of the pump, you might consider removing those bolts and the flange to replace the o-ring that seals the flange, that could cause a problem if that o-ring is aged. I hope you get it sorted out. Cheers

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Fieldtech59
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Fieldtech59, Shop manager
Category: Construction and Road Equipment
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Experience: Construction equipment repair technician since 1986, JLG certified, Shop manager since 2006.

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