New Hydraulic pump, loud whining sound, L4740

[BayouB2601]

A few weeks ago I posted about the hydraulic pump on my L4740HST crapping out on me. Ordered the replacement, Kubota OEM pump and had it installed by a buddy that is a mechanic for the local Kubota dealership. All the hydraulics seem to be working great… HST, loader, pto, 3-pt lift, rear remotes and 3rd function valve. when I changed the pump I changed the hydraulic fluid, KUBOTA Super UDT 2 (synthetic) and both hydraulic filters (Kubota Brand). The fluid levels are just right and the fluid in the transmission case isn’t frothy or bubbly, it looks normal and clean. I’m at a loss for what could be the cause of the whine. it is such a load whine I’m concerned something isn’t right and I can’t afford to have anymore downtime or buy another $1200 pump.
I’ve ordered a pressure gauge so I can check the systems pressure. Could an incorrectly set pressure release valve cause this, or possibly a bad pressure release valve? Should I have used the older UDT hydraulic fluid and not the synthetic?

Any advice would be greatly appreciated. Thank you.

 

[85Hokie]

I dont think the fluid is the problem.

Before the switch - you heard what it sounds like WHEN the relief valve kicks in? (picking up something too heavy on the loader) Is it this sound?

To me it sounds like there is a hydraulic connection that is causing a "dead head" situation.

Have you tried to disconnect the loader ?

 

[TheOldHokie]

A few weeks ago I posted about the hydraulic pump on my L4740HST crapping out on me. Ordered the replacement, Kubota OEM pump and had it installed by a buddy that is a mechanic for the local Kubota dealership. All the hydraulics seem to be working great… HST, loader, pto, 3-pt lift, rear remotes and 3rd function valve. when I changed the pump I changed the hydraulic fluid, KUBOTA Super UDT 2 (synthetic) and both hydraulic filters (Kubota Brand). The fluid levels are just right and the fluid in the transmission case isn’t frothy or bubbly, it looks normal and clean. I’m at a loss for what could be the cause of the whine. it is such a load whine I’m concerned something isn’t right and I can’t afford to have anymore downtime or buy another $1200 pump.
I’ve ordered a pressure gauge so I can check the systems pressure. Could an incorrectly set pressure release valve cause this, or possibly a bad pressure release valve? Should I have used the older UDT hydraulic fluid and not the synthetic?

Any advice would be greatly appreciated. Thank you.

Sounds like something is wrong. I think I would check the inlet pressure at the loader valve. With everything in neutral it should be no more than 100 PSI.

Dan

 

[North Idaho Wolfman]

Make a video of the sound!
Other options to a hydraulic output issue would be a power in issue.
It's possible you have a bad bearing on the gear that drives the pump.
Or maybe bad teeth on the gears.

 

[BayouB2601]

I dont think the fluid is the problem.

Before the switch - you heard what it sounds like WHEN the relief valve kicks in? (picking up something too heavy on the loader) Is it this sound?

To me it sounds like there is a hydraulic connection that is causing a "dead head" situation.

Have you tried to disconnect the loader ?

It’s not the same sound as the relief valve opening, definitely not that loud or harsh sounding. I agree, it sounds like it could be “dead heading” . I disassembled the 3rd function valve and checked It because it was sticking occasionally. I didn’t see any problems but it’s still sticks every once in a while. I’ll try disconnecting the loader lines in the morning and see what that does.

 

[BayouB2601]

Make a video of the sound!
Other options to a hydraulic output issue would be a power in issue.
It's possible you have a bad bearing on the gear that drives the pump.
Or maybe bad teeth on the gears.
View attachment 110686

I replaced the pump along with all the gears and bearings (new o-rings too). I had to replace them, they were chewed up and missing teeth from the original pump breaking. I’ll make a video of the sound and post it. Thanks for the suggestions.

 

[TheOldHokie]

It’s not the same sound as the relief valve opening, definitely not that loud or harsh sounding. I agree, it sounds like it could be “dead heading” . I disassembled the 3rd function valve and checked It because it was sticking occasionally. I didn’t see any problems but it’s still sticks every once in a while. I’ll try disconnecting the loader lines in the morning and see what that does.

Guessing is not axfruitful diagnostic tool. Check the loader valve inlet pressure. Tee the gauge into the supply line and run the loader through its paces. That will tell you exactly what the pump is seeing pressure wise.

Dan