I bought the L3800 new in 2012. I stored the backhoe on the ground so that the bucket and arms were on the ground. The first time I used the backhoe I noticed that hydraulic pressure would not hold and I was constantly adjusting the arm's vertical position. I stored it over the winter and most of this summer. When I mounted it last week I noticed that it was still not holding pressure. It would start dropping immediately after trying to position it off the ground. The hydraulic fluid level is appropriate and the hoses are not leaking. What should I be looking for?
backhoe on my L3800 won't hold hydraulic pressure
- Thread starter scjbob
- Start date
85Hokie
Moderator
Staff member
Lifetime Member
Equipment
BX-25D ,PTB. Under Armor, '90&'92-B7100HST's, '06 BX1850 FEL
How long did you operate it as it was dropping? good enough to get ALL the possible air out??? Could it be your valve body??
The first time I used it to dig a culvert I used it for an hour. Last week I only used the hydraulics to re-mount the backhoe to the tractor to move it to the barn for the winter. Should I cycle the hydraulics multiple times? Does it matter what RPM the engine is idling at when using the hoe? Somewhat of a newbie when it comes to tractors.
85Hokie
Moderator
Staff member
Lifetime Member
Equipment
BX-25D ,PTB. Under Armor, '90&'92-B7100HST's, '06 BX1850 FEL
I would cycle it , and run the rpm's up at 75% of WOT after hook up, I would not use the hoe at all at idle - some machines will not even pump well until rpms get in the "right" range .......
run it up near what the max rpms are for your tractor, see if there is any difference at all. Report back
Will do. I won't be back at "the farm" until Friday but will give it a try and report back. Thanks for the suggestions.
Some three point backhoes reccomended rpm is 540 pto speed. No faster. The manual for the kubota at work is inteded to run at pto rpms. As far as leaking down, its either a leaking valve or a damaged seal in cylinder.
To test it, lines nned to be removed and plugged and capped.then raise/lower hoe to see if plugged cylinder leaks down. With cylinder capped off and suspended, if it leaks down its cylinder, if it doesent leak its hyd control.
To test it, lines nned to be removed and plugged and capped.then raise/lower hoe to see if plugged cylinder leaks down. With cylinder capped off and suspended, if it leaks down its cylinder, if it doesent leak its hyd control.
Last edited:
I'll try cycling them first. I ran it at PTO speed the other day but did not cycle the backhoe at all. I suspect that connecting and disconnecting the backhoe has allow some air into the lines now that I think about it. Could be wrong though so if none of that works I'll trouble shoot as you suggest. Although this tractor is fairly new and only has 100 hours on it there is always the possibility that it has a defective part(s). Thanks.
85Hokie
Moderator
Staff member
Lifetime Member
Equipment
BX-25D ,PTB. Under Armor, '90&'92-B7100HST's, '06 BX1850 FEL
If this is PTO driven, then 540 is the right answer, HOWEVER getting the PTO to that speed usually means 90% of WOT - most tractors ratio of engine speed to pto speed is in the upper 90% or engine throttle. Running an engine at a lower rpm is worse than running it wide ass open. Never under run a diesel or hydraulic pump, both have an operating range and the low end isnt it.
Billdog350
Member
Equipment
Kubota L3710 HST,L2230A QT,forks,Takeuchi TB125, 60" Luck Now pto Snowblower
I would definitely cycle the BH in all directions with all cylinders several times. Additionally, if you haven't used it in a long time, there is a chance that the seals never got a chance to properly seat. Just exercising the BH using it for normal use will renew any seals that are dry. If the issue doesn't improve by the time you have an hour on it or so, then you could need repacking of the cylinders or a new valve body, however those are less likely on something with minimal use so look toward the obvious things like air in the system.
My manual (3800HST/BH77) says to run the engine at 2700 RPM while using the backhoe. It also says that "if necessary" for noise reduction, etc, you "can" operate it at 2000 RPM.
That wording implies to me that 2000 RPM is min engine speed for backhoe operation - and that 2700 is better/optimal.
Good luck,
Wally
That wording implies to me that 2000 RPM is min engine speed for backhoe operation - and that 2700 is better/optimal.
Good luck,
Wally
85Hokie
Moderator
Staff member
Lifetime Member
Equipment
BX-25D ,PTB. Under Armor, '90&'92-B7100HST's, '06 BX1850 FEL
My manual (3800HST/BH77) says to run the engine at 2700 RPM while using the backhoe. It also says that "if necessary" for noise reduction, etc, you "can" operate it at 2000 RPM.
That wording implies to me that 2000 RPM is min engine speed for backhoe operation - and that 2700 is better/optimal.
Good luck,
Wally[/QUOTE
at 2000 rpms .......that is like asking YOUR heart to beat at 60 bpm while running away from a pissed off bear.........
just saying, if you want to use the machine to "work" - work the machine - dont baby it - and if noise is a problem........well dont get me started !!!
I've got a PTO pump on my backhoe. It works just fine at ANY engine speed. Faster pump speed gives you faster movement. I usually run mine around 1800-2000RPM, which probably translates to 400ish RPM?
I'd like to see a Kubota manual that says there is a minimum pump speed and their justification for it. If we're talking PTO mechanical pumps, I don't see it.
I'd like to see a Kubota manual that says there is a minimum pump speed and their justification for it. If we're talking PTO mechanical pumps, I don't see it.
My frame-mount commercial Kubota backhoe has the same language (as previously noted this thread) in the Owner's Manual about engine speed(s) to operate backhoe.
Maybe...but I too don't see any difference if it's a mechanical hydraulic pump.
Sure, if you're uprooting a boulder or pushing in a chimney or tree, then run it at rated RPMs for maximum 'work' pressure. For 'gentle' or even precise trenching or digging a tree hole in decent soil where speed is the lesser consideration, throttle back: get a slower response and perhaps better control. Especially for those of us that don't have 2,000-hrs riding a 'hoe as employment.
At recommended throttle setting if I'm not paying attention I'll whip that boom from side-to-side with a snap that can easily dent the thing it hits--and it seems like something's always in the way. Or banging the side of a truckbed when craning a load. Rarely do I find myself trenching in the middle of a pasture.
Spouse especially even with light touch on controls (lighter than mine by far) sets it just above idle when using the 'hoe and although a bit slower, gets the job done. Probably works well 90% of the time. Sometimes has to run up the RPMs for that extra effort when breaking a root or hitting a snag.
I've never seen any ill effect from throttling back to a slower operating RPM.
I'm curious other perspectives. Please post back and continue this conversation.
Maybe...but I too don't see any difference if it's a mechanical hydraulic pump.
Sure, if you're uprooting a boulder or pushing in a chimney or tree, then run it at rated RPMs for maximum 'work' pressure. For 'gentle' or even precise trenching or digging a tree hole in decent soil where speed is the lesser consideration, throttle back: get a slower response and perhaps better control. Especially for those of us that don't have 2,000-hrs riding a 'hoe as employment.
At recommended throttle setting if I'm not paying attention I'll whip that boom from side-to-side with a snap that can easily dent the thing it hits--and it seems like something's always in the way. Or banging the side of a truckbed when craning a load. Rarely do I find myself trenching in the middle of a pasture.
Spouse especially even with light touch on controls (lighter than mine by far) sets it just above idle when using the 'hoe and although a bit slower, gets the job done. Probably works well 90% of the time. Sometimes has to run up the RPMs for that extra effort when breaking a root or hitting a snag.
I've never seen any ill effect from throttling back to a slower operating RPM.
I'm curious other perspectives. Please post back and continue this conversation.
Sorry, I'm with Stubbyie here. I run my d-17's backhoe just above idle all the time. It's just slower. The pump doesn't really care, but it's a standard pump, I don't know what the manual says for this pump. It changes with the type of pump. Odd thing is, it's almost as strong there as at full rpms.
Some pumps require the rpms to overcome the internal backflow present in them. Worn pumps have various amounts of back flow and some designs (vane, gear) can also have inherent backflow internally when under pressure. Check valves stop this from happening outside the pump but inside... it's a design choice or wear problem.
One thing to keep in mind is that unless you are a highly skilled operator, there are dead/slow spots in your work patterns. At high RPM's you are wasting more fuel in those spots.
My father always taught me to run at the lowest RPM that effectively does the job. Saves wear on the engine, parts, and fuel.
I did use a rental unit once that had an auto throttle on it, that was really cool. It only used the throttle necessary to do the job. I'm sure it was a bugger to repair, but it was nice to use!
Some pumps require the rpms to overcome the internal backflow present in them. Worn pumps have various amounts of back flow and some designs (vane, gear) can also have inherent backflow internally when under pressure. Check valves stop this from happening outside the pump but inside... it's a design choice or wear problem.
One thing to keep in mind is that unless you are a highly skilled operator, there are dead/slow spots in your work patterns. At high RPM's you are wasting more fuel in those spots.
My father always taught me to run at the lowest RPM that effectively does the job. Saves wear on the engine, parts, and fuel.
I did use a rental unit once that had an auto throttle on it, that was really cool. It only used the throttle necessary to do the job. I'm sure it was a bugger to repair, but it was nice to use!
I suspect some of it comes with the hydrostatic machines, I'll call it the skid steer usage model. You set the throttle, which spins the pump, then you use as much of it as you want/need to move the machine, lift the load etc.
This differs greatly from the gear drive models, where your engine speed and wheel/PTO speeds are directly linked. You don't really use any more throttle than you need. I do all kinds of work at or just above idle when I am in a tight spot or being careful. I notice very little difference in my hydraulic capability at idle other than speed.
This differs greatly from the gear drive models, where your engine speed and wheel/PTO speeds are directly linked. You don't really use any more throttle than you need. I do all kinds of work at or just above idle when I am in a tight spot or being careful. I notice very little difference in my hydraulic capability at idle other than speed.