Backhoe thumb retrofit

[bobsphotos]

I switched my Woods BH-80X manual thumb to a hydraulic thumb which runs off my 3rd SCV remotes. It works awesome but I do have one question for the guru's. When I swing the thumb out about 1/2 way and then curl the bucket to meet it, I can move the bucket backwards if I swing the thumb towards it. If I then release the thumb pressure the bucket bounces forward. My concern is that I am not sure what is happening from a hydraulic standpoint. I think that the thumb has more mechanical advantage. Any thoughts?

 

[AKKAMAAN]

I switched my Woods BH-80X manual thumb to a hydraulic thumb which runs off my 3rd SCV remotes. It works awesome but I do have one question for the guru's. When I swing the thumb out about 1/2 way and then curl the bucket to meet it, I can move the bucket backwards if I swing the thumb towards it. If I then release the thumb pressure the bucket bounces forward. My concern is that I am not sure what is happening from a hydraulic standpoint. I think that the thumb has more mechanical advantage. Any thoughts?

If the force from thumb can move the bucket so the bucket cylinder get pushed in (retract), there is a hydraulic problem.....If not the movement in bucket comes from excessive play in the linkage between the cylinder and the bucket

You need to tell how much you can move the bucket with the thumb....

There is a natural play in any linkage. After some hundreds of hours of use, this play increases (wear prevention by using the grease gun every 8 hrs of digging) an will show some considerable movement on the edge of bucket...there are 1 connection pin on the capped side of cylinder and 3 connection pins on the rod side of cylinder....manually check the play in these connection pins...together they will add up to a considerable free play

 

[bobsphotos]

Thanks for the info. The backhoe only has about 50 hrs on it so it shouldn't have much linkage play but I will take a much closer look at it tonight. I also thought that I might put a piece of masking tape around the rod 9 about 2 inches out and try to get a sense of actual rod movement back into the cylinder.

 

[J_J]

You could add a relief valve to the thumb cyl and set the pressure to whatever to suit your purpose. If the cyl are the same, as in tons of force, then the one with the best mechanical advantage will overpower the other, and perhaps break something.

There might be air in that cylinder or the valve is leaking. Does the cyl extend back out when you let off the thumb?

 

[bobsphotos]

When I back of the thumb, the bucket snaps forward.

 

[bobsphotos]

Could I add an inline relief valve?

 

[J_J]

https://www.surpluscenter.com/item.asp?item=9-6135-50-H&catname=hydraulic

 

[bobsphotos]

JJ,
If I decide to go the route of an in-line relief valve, I have to assume tht the relief port gets sent back to the tank, but is there an easy way to do that. I am using a set of rear remotes.

 

[J_J]

Sure, just tee the relief outlet to any return hose.

Does your SCV have work port relief?

 

[bobsphotos]

JJ,
If I only put a relief valve on the line that extends the cylinder, can I tee the relief port back to the line that retracts the cylinder or would that try to pressurize that line?