Backhoe Mechanical or Hydraulic thumb?

[graydog]

J J Herewith are pictures. The blue ribbons mark the input and outlet for the thumb hydraulics. Hand is on the foot pedal.
I don't know why the input comes off the supply line from the tractor, rather than the supply side of the valve. (I know there's a reason, just not what?)

 

[graydog]

dfkrug, I'm thinking about the dual pump configuration. The hoe has three hoses from the tractor, I assume two inputs and one return. The two input hoses are on the right end of the valve block, with the boom swing valve between them. I don't know from following hoses whether boom swing is powered by a different pump than the rest? But if so bucket and thumb are together on the other?

 

[dfkrug]

dfkrug, I'm thinking about the dual pump configuration. The hoe has three hoses from the tractor, I assume two inputs and one return. The two input hoses are on the right end of the valve block, with the boom swing valve between them. I don't know from following hoses whether boom swing is powered by a different pump than the rest? But if so bucket and thumb are together on the other?

Interesting pix, GRAY. Some surprises there:

I thought he L39/45 used the BT1000 hoe. I have not seen that hoe
designation, BH4949.

Your valve block shows only 3 shock-RVs.

The ribbons indicate the added thumb plumbing, correct?. The tee
into a work port is surprising, assuming that IS a work port. I do
not know your plumbing config.

The thumb control...is it supposed to close when you put your foot
down, then retract automatically when you take your foot off? That
is how it works on the excavator I operated. On your backhoe, that
kind of control is not simple, and may point to your problem.

As I said, I don't know the L39/45. You need to trace the hose
routing and look at the hydraulic diagram in your service manual. One
return line for both hoe pumps is OK.

 

[graydog]

The hoe is indeed a BT1000; the ID plate is on the thumb.

Are the shock RVs the pointy bits facing down from the valve block?

Ribbons are on the added plumbing. The tee is on the larger of the two supply lines, not a work port.

Function of the foot pedal is two-way: retracts when you rock one way, extends the other way. Come to think of it, maybe that's why it's piped with a live supply and a ported relief?

The service manual -- we were gonna get to that. Somewhere one of you has linked me to a source, which I will get going on. The tractor comes with one of those books that shows what the pedals are for, which is not nothing in my case!

One more question: do I need a Kubota tech, or a competent hydraulic tech? There are CAT, Case, Deere and Bobcat shops within seven miles....

Thanks!

 

[graydog]

Did someone use spools for the thumb that had regen on it?

J J, can you expand a bit on this? (See, I'm learning enough to hear the questions!)

 

[dfkrug]

Are the shock RVs the pointy bits facing down from the valve block?

I believe they are the longer units hanging down off the valve block,
with the 2 hex nuts at their ends. Check with your manual when you get
it.

Ribbons are on the added plumbing. The tee is on the larger of the two supply lines, not a work port.

Generally, we don't tee off supply lines (pressure IN) in open center
systems. If your added valve is OC (probably is), it has to get its
supply from the power beyond OUT of the last valve in the stack for
one of the pumps, or it goes before that same stack.

Function of the foot pedal is two-way: retracts when you rock one way, extends the other way. Come to think of it, maybe that's why it's piped with a live supply and a ported relief?

...

One more question: do I need a Kubota tech, or a competent hydraulic tech? ....

That kind of thumb control makes sense.

Getting a competent hyd tech guy is more important than a brand-
specific guy (or gal), IMO. I have seen techs at dealers struggle to
figure out how to properly add a valve, for example, even when they
have success fixing existing systems that have failed.

 

[mike69440]

Nothing wrong with being familiar with the existing system, but it's not really necessary. That's because it's normal practice is to plumb the thumb system with relief valves anyway. The reason being that either the bucket forces the thumb or the other way round....and in either case both systems have to have relief valves and bypass lines to avoid breaking something expensive. So just build it that way and as a bonus you can simply do some cautious experimenting and set the relief pressure appropriately.

That's how most backhoes work and it's also how Kubota solves the problem of relative hydraulic strength with the hydraulics in their stock backhoes. Our M59 came with either 8 or 10 adjustable relief valves mounted in a double row right onto the backhoe lever manifold. The bypass lines are internal to the valve block. Kubota set the pressures at the factory, but there's been some adjustment required since. That's pretty much typical.
rScotty

Surplus Center sells a 4 port Prince adjustable releif valve that works ok for small thumb.

 

[Stonehaller]

It looks like the rod end of the cylinder is piped to one port of the thumb control valve and the other end is teed into the return line. That would do what you say, extend slowly on its own and retract rapidly. With return pressure on the piston side all the time, the thumb would have no power. The L39 does have a separate swing pump. When looking at the valve from the back of the tractor, the main supply hose is on the far left of the valve pack and the swing supply hose is on the far right. The return line, where your thumb is teed in, is between the swing control valve and the rest of the valve stack.

I see in the parts manual for the BT1000 there is a kit for auxiliary hydraulics that is connected just as yours, but it looks to me that the kit was not designed for a hydraulic thumb.

If the foot pedal works the valve in both directions, you could move the line from where it is teed in to the return line over to the other port on the valve, but you should have a relief valve in the line on the piston side of the thumb cylinder. If the foot pedal does not work the valve in both directions you could add a separate detented valve on the outlet of the foot control valve to control the direction of the thumb. Get a valve with a built in relief.

 

[graydog]

Stonehaller, this is most helpful. Let me work on this a bit, and I'll BRB!

 

[graydog]

Okay, the tractorparts.com pdf (hydraulic kit) shows exactly what has been added. Looks simple enough move the return line to the valve, get a Prince RV-2H inline relief valve and some hose bits, and pipe the overflow into the tee. I'll talk to the dealer about whose hands are gonna get oily here.
Thanks to all!