Hydraulic pump failure on Kubota B7100

Ron Pool

unread,

May 27, 2000, 3:00:00 AM5/27/00

to

I'm helping my father install a Great Bend front-end loader on a
Kubota B7100 (gear driven) tractor. The loader's hydraulic controls
were connected in line with the tractor's existing hydraulic lines,
but the in and out lines to the loader controls were reversed. Upon
starting the tractor with the incorrectly installed loader controls,
the tractor's hydraulic pump's housing cracked and leaked out lots of
oil. The crack is on the intake side of the pump, and fluid pours out
of the pump, but not under high pressure.

In addition to hooking the hydraulic lines up backwards, we totally
filled the transmission of the tractor with the proper gear oil (not
to the proper fill point, but completely full). The transmission case
serves as the source of hydraulic fluid in this tractor.

Does anyone have an idea as to why the pump cracked? I'm guessing
it's either because the hydraulic lines to the loader controls were
connected backwards, or that totally filling the transmission case
(well above the level it should have been filled to) caused this.

In case it helps to picture this, here's a text picture of the system
before and after adding the loader controls.

Before adding new loader controls:

tractor control ======== Reservoir ==================== Pump
| |
+========================================================+
<--- direction of fluid flow

There is some internal connection from the tractor control to the tractor's
three-point-hitch liftin cylinder.

After adding new loader controls:

We've ordered a new hydraulic pump, but I want to make sure I know why
the old pump failed before we replace it. I'll correct the backwards
loader control connection and the fluid level before we try it again,
but I want to make sure there's nothing else that could have caused
this (such as a defective loader control).

Thanks for any insight or advice on this.

-- Ron
--
Ron Pool Internet: am...@cornell.edu
Computer Services, NYSAES; Food Research Lab; West North St.; Geneva, NY 14456

JC

unread,

May 29, 2000, 3:00:00 AM5/29/00

to

Are the controles on the loader for right kind of system? There are two kinds of
systems, an open center and a closed center system. If the tractor has an open
center system and the valve on the loader is for a closed center system you could
have the problem you described. An open center system flows oil through the system
all of the time. A closed center system holds the oil at system pressure at all
times. The way your diagram looks, if the tractor has an open center system and
the valve is for a closed center system all oil flow will be blocked and the
pressure will build up untill something gives, because the relief valve probably
is in the tractor control valve. All parts must be for the same type of system.
The easiest way to hook up a loader is to a remote coupler, but the valve still
has to be for the same kind of system.
I hope this helps, John

JC

unread,

May 29, 2000, 3:00:00 AM5/29/00

to

Also even if the control valve is the right type, with the way you have it hooked up
you MUST have a relief valve on the in side of the valve you added. Without it, as the
cylinder reaches the end of the stroke, it could cause the same damage