Bobcat 743 lift dip

[Markle]

Hello fellow wrench turners …my 743 s/n 13033 was brought to life 1 year ago with a new crate engine, and lots of detail items such as replacing iffy hoses and steel hyd tubes, ujoint, all fluids and filters…no leaks anywhere…and everything was working perfectly. Til yesterday using the machine in a tree nursery , the lift function developed a bug. In any boom position, when pressing the heel to lift, there is a momentary drop before the expected boom rise. so, pressing slowly with heel intending to lift, the boom will drop…continue heel press further, boom rises ok with no more issue. No jerks. Boom drops as expected with toe press. No hesitation, very smooth. It's like there's a dead spot in the spool valve position for lift. I never had to go into the spools on any of my bobcats, but I see in the service manual that there are seals on each end of the spool rod, and mine aren't leaking. so the problem is dependent on spool rod position. What's inside the spool valve housing that would cause this? Thank you in advance.

 

[brdgbldr]

There are seals inside the control valve.
Take a look at the parts catalog for your serial number and look at the control valve exploded view:

Bobcat Parts Catalog - Find Diagrams for Your Equipment - Bobcat Company

Locate all parts and component information about your Bobcat equipment with detailed visual diagrams and illustrations with parts numbers and add to your list.

www.bobcatpartsonline.com

 

[Markle]

Thank you. I looked at the service and parts manual. There is a relief valve and an anti cavitation valve in the lift section with the lift spool. there doesn't seem to be any other seals along the spool rod, only at each end preventing external leaks. I'm thinking the relief valve may be malfunctioning…if you had the same issue I'm wondering what the fix might be? What does the anti cavitation valve do?

 

[brdgbldr]

Here is a website to explain cavitation:

Cavitation in Control Valves | Emerson US

Fisher anti-cavitation trims for control valves help eliminate or control cavitation damage in clean and dirty service.

www.emerson.com

In short it is when bubbles are created in fluid and implode. This can cause damage to parts.

I would take a look at the check valve. Here is a statement from a Bobcat diagnostic book:
"Load Drops Slightly When Going From Neutral to Raise Position
If the lift arms and bucket function normally, but the load drops slightly when you move the lift cylinder spool or tilt cylinder spool from neutral to raise (or extend), suspect the associated load check valve is leaking. Check the load check valve for worn O-rings, poppet, and seat and repair/ replace as necessary."

 

[Markle]

Thank you brdgbldr! That's exactly the symptom. The parts manual doesn't call it a "load check valve" in the lift section of the control valve bank. They call it "port relief" and of course it is NLA from Bobcat ( no longer available). Does anyone reading this suggest a source? Valve poppet and/or seal kit?

 

[Markle]

To update this for the archives, I found an excellent resource (individual) in South Dakota who has the knowledge and parts. Not sure the rules here allow me to name the business. The load check on the lift section of the hydr valve gang is under the port relief. Spring and poppet inside after removing the relief valve. Now I just have to do the work.

 

[Tango-Charlie]

Hey Markle,
Can you PM me with the guys contact information?
Thanks

 

[Markle]

Hey Markle,
Can you PM me with the guys contact information?
Thanks

how do I do that…click on your handle and add it under your profile where it says "write something".?

 

[cdmccul]

how do I do that…click on your handle and add it under your profile where it says "write something".?

"Start a conversation"

 

[Tango-Charlie]

Hey Markle, thanks I got your PM and information.
Thank you!!!!

 

[oiu789]

Easy cylinder or load ceck leak by check. Raise a load a few inches high crack a line on the ram side and see if load drops. If it does it could be seals in the cylinder or your load check. When in neutral it is a closed system when you crack a line loose this will allow some air in if some thing is leaking by the load will drop if it is cylinder seals oil will leak from the loosed line under some pressure until the load rest on the ground. A little messy have some thing to catch the oil ready and watch your toes.