L4400 HST 3PT/Steering hyd. pump rebuild

[CptTrog]

I've killed the hydraulics on my 'Bota L4400H using the BH90 to dig a septic system. I fear I got the system's hydraulics far too hot. The top boom cylinder even got too hot to touch along with the lines. Backhoe stopped suddenly and now I've got a lovely whining/grinding/spinning noise coming from the pump area at engine shut down.
I've got no hydraulics to the front bucket or backhoe at all, even after an overnight cool down. At least the trans is working so after using a winch to get everything up, I was able to get it into the barn.
I've researched my shop service manual (great investment), user manual and used the Kubota.com Illustrated parts site to find both the pump as well as the exploded parts showing all the components. (T1150-36403 pump assy)
I'm here asking for advice on two things:
1. After checking the relief valve settings and everything else I know of that may have accidentally and/or purposely engaged disabling the hydraulics, is there anything else (levers, buttons, knobs, chants, spells, animal sacrifices) that I should look at? The no steering leads me to believe I've truly killed the pump.
2. If I'm to rebuild the pump -barring any galling or breakage inside the housing- are there any known "gotchas" I should be aware of that are not listed within the service manual itself? Any tips or tricks some of you might have?

One last thing, I recently changed the hydraulic fluid (did not do a flush)after a broken line replacement as well as both filters so contamination should not be a factor. Levels were correct so no cavitation that I'm aware of. Heat is my only suspect.

TIA

Cpt. Jera

 

[David_Kb7uns]

Check the hydraulic pump and drive.

Not saying that your machine is affected but had a service bulletin on my Grand L3130, where the pump drive could shear off from poor lubrication if used for extended periods of time with front down attitude of tractor while using a backhoe. Kubota would only do the fix upon failure, I did the fix because I do digging with the backhoe and the cost to move broken un-drivable tractor would be more then the fix.

The repair was a new oil filter holder with calibrated orfice and pump holder with a lubricating line running from the oil filter holder to the pump drive gears and pump holder bushings.

Loosing the loader backhoe hydraulic section of the pump and the steering section of pump means probably no pump drive, if it is HST you may be lucky it still has enough oil in it as the charge usually comes from the steering circuit.

If you sheared the pump drive not sure if you can get the parts to fix may be better to replace.

David

 

[CptTrog]

Thanks, David. I've got the local Kubota dealer trying to see if my machine fits this bulletin. I'm inclined to believe it is since this pump has failed in this exact same configuration once before. They made good on the first one. Since I've been out of warranty since 2011 and the bulletin only extended the pump replacement for two years past that, I've little hope of any help on their part.
We'll see.
Thanks again.

 

[CptTrog]

Found the problem. Gears don't mesh that well when they're this slick!

 

[CptTrog]

Ordered the parts today for drop ship to the farm on Friday. $350 and change.
Got off easy, I think.

 

[David_Kb7uns]

Well it was a pump drive problem, think I have seen another one where it got stripped out. It explains the buzzing, better then the whole shaft sheared off from seizing up.


David

 

[CptTrog]

Agreed, David. Think I'll heed the advice on another forum and check the high pressure relief. Also going to investigate upsizing the oil cooler. Seems a bit undersized for that class of machine with that much volume of fluid.

 

[CptTrog]

Okay, gang. I got the parts in and rebuilt the pump taking great care to ensure it went back together correctly. I've now got power to the implements but the pressure is nowhere strong enough to move things normally. The power steering won't work unless the front tires are elevated off the ground and then is extremely stiff.
I've followed the service manual for break-in to the letter. I've drained the system, flushed with 10.6 gallons of new fluid, elevated all tires and turned the tranny for 20 minutes in low range, drained and refilled the fluid and changed filters.
I've dissembled the 3rd function valve and checked for shavings and cleaned thoroughly of anything that might cause it to hang, as this has been an issue in the past.
Still, barely enough pressure to move implements and still no power steering.
Suggestions?
TIA

 

[CptTrog]

Well, folks. I've discovered my 2nd issue's cause. I have only 500psi because I (am a dumbass for not looking at the H20500 exploded pump view closely enough) installed a "side plate" upside down blocking the gears' lube port during the pump rebuild.

Smoked the plate and the rubber double-ring on the face behind it but the gears and housing appear to be fine. Deformed and cracked the plate quite nicely.

So, another plate and ring ordered which will arrive next Wednesday. Should solve my problem. Meanwhile, I bought a 3000psi gauge, hose and T and installed it at my BH hyd. connection at the rear of the tractor. Spent about $65 but I feel it will be insurance and well worth it. (Will try to post a pic of the assy later)

Now if I can find a place to install a temp gauge transducer in the system and mount a gauge in the dash, I'll be set. Want to ensure I don't overheat or overpressure the system in the future. I'll be able to view the gauge from either the driver's seat or the BH90 operator's position.

If anyone has a suggestion on an install point for the transducer, I'd be grateful.

Thanks, everyone.