Hyd. thumb

[BIGDAN315]

I just built a hydraulic thumb for my Kamatstu pc 40 excavator. The problem is I can't get it to retract on its own.It has to be pushed back by the bucket.No problem clamping though. Of course the machine has auxsillary hyd. WHen I try to retract or pull back the thumb it just sits there and sounds like the pressure reliefe valve is dumping?
Any body have any inputs on what might be wrong ? I have used it the way it is but a bit of a pain when the thumb does not stay all the way back. Otherwise it works just fine.

[mikef87]

You must have 2 way hydraulics? Not to sure

[dirthog]

check the lines out the boom I believe you will find one is pressure and one is tank on most small excavators you can change one line at the base of the boom to make it two way flow

[BIGDAN315]

ok dirthog I will give it a try..thanks

[CascadeScaper]

That's what it sounds like. The line that is supposed to retract the thumb is a return to tank, unpressurized line. This is used for breakers or hoepacs that only use 1 way hydraulics.

[BIGDAN315]

That's what it sounds like. The line that is supposed to retract the thumb is a return to tank, unpressurized line. This is used for breakers or hoepacs that only use 1 way hydraulics.

I see so how do I make it a pressure line.:confused:

[dirthog]

Check and see if there is another port comeing out where the lines hook up at the base of the boom you will have to switch the tank line to it. should be the pressure line from the other side of the valve that works the breaker.

[w2bstoned]

the old bobcat had a selector valve that you pulled, Give the dealer a call?

[KAC=CATeater]

I cant remember off the top of my head but on many kac excavators there is a selector valve that shows a breaker and a grapple. You just have to turn the valve to grapple. Your particular unit may or may not have this valve on it, but if you see one (usually under the right hand cover) put it in the other direction.