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Curtis B.
Curtis B., Technician
Category: Construction and Road Equipment
Satisfied Customers: 28917
Experience:  Technican turned service manager with multiple lines of equipment and rental units.
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I have a bobcat 873 F Series. I've replaced a hydrualic hose

Customer Question

I have a bobcat 873 F Series. I've replaced a hydrualic hose and repacked several cylinders. I've re-filled the hydrualics with AW46. I've got s severe shuderring in the tilt and lift.
JA: Sometimes things that you think will be really complicated end up being easy to fix. The Heavy Equipment Mechanic I'm going to connect you with knows all the tricks and shortcuts.
Customer: ok
JA: Are you fixing this yourself? What have you tried so far?
Customer: just made sure there are no leaks. Looked at pedal linkage. May need bushibgs but it was only mild before I did the cylinder and hose repair. I'm a good car mechanic and have Bobcat manual but don;t know my way around the 863.
JA: Anything else you want the equipment mechanic to know before I connect you?
Customer: I did check the left side drain filter. No issues. Replaced. Could not get to the right one. Did when I replaced filters and topped up fluid per manual. Ok
Submitted: 2 months ago.
Category: Construction and Road Equipment
Expert:  Curtis B. replied 2 months ago.

Hello! Let's see if we can work together and come to a satisfactory conclusion!

Expert:  Curtis B. replied 2 months ago.

Check the suction pipe to the hydraulic pump, may be sucking air or has a restriction, which will draw air into system, causing the shuttering.

Customer: replied 2 months ago.
Curtis -
where is the hydraulic pump? I have the service manual but need some direction.
Customer: replied 2 months ago.
As its not a good print
Expert:  Curtis B. replied 2 months ago.

Hydraulic pump is the small pump on the end of the two drive pumps

Customer: replied 2 months ago.
Ok. I'll have to pick this up in a few days after i get back in town. Is that ok?
Customer: replied 2 months ago.
Btw - the shudder is on the way down on the lift. Never on way up. Does that help?
Expert:  Curtis B. replied 2 months ago.

That could mean the control valve has problems with the load checks , which have to open when you lower boom. Will not be suction problem!

Customer: replied 2 months ago.
It had a slight shudder before I replaced hose and re-packed 3 cylinders and changed filters and topped up fluid but not like this.Not running it of course. I can re-diagnose if I need to.
Expert:  Curtis B. replied 2 months ago.

The load checks, may have debris or dirt in them, Look at the small valves with springs, between the two valve sections in your parts book.

Customer: replied 2 months ago.
I've got an 800 page service manual and Bobcats on line catalogue. When I look at the Hydrualic schematic in the service manual I see multiple references to control valves. Apologise that I don't understand the flow.
Customer: replied 2 months ago.
Wait a sec - found the Hydraulic Control Valve section in my svce manual
Expert:  Curtis B. replied 2 months ago.

You have a single control valve for the bucket and boom, i may have an auxiliary spool too. But this control valve has the check valves , between the sections. They may not be called load checks, just check valves, or recirculating valves.

Customer: replied 2 months ago.
This section?Load Check Valve
Loosen the load check plugs (Item 1) [A).
Assembly: Always use new O-ring. Tighten the plug to
35-40 ft.-Ibs (47-54 Nm) torque.
Remove the load check plug [8] .
Remove the spring and poppet [C).
Expert:  Curtis B. replied 2 months ago.

That sounds like it, remove them and examine for debris or blown o'rings.

Customer: replied 2 months ago.
Not to digress - but when I look under the cab I see a couple of disconnected connectors. Been that wait. Have no idea but wanted to share. Full disclosure. Only 1400 hrs on machine. Use sparingly around property.
C1 Load Check Valve/Lift Function
C2 Load Check ValvelTiit Function
Above inschematics on page 2-21
No fluid pressure on them correct?
Expert:  Curtis B. replied 2 months ago.

With engine off, there will be no pressure.

Customer: replied 2 months ago.
Sorry about typos.Ok. Suggestion. I need to study schematics and understand system better. I have to be away from this for 2 days. Why don;t I study the schematic and then look at the valve. Then if I need to get you on the phone it will be less painful for you. Can we do that at the end of the week?
Expert:  Curtis B. replied 2 months ago.

Sure, I should be close.

Customer: replied 2 months ago.
Ok. I'll get back to you.
Expert:  Curtis B. replied 2 months ago.