I have recently purchased a L3901 with the FEL and the BH77 backhoe. It currently has a mechanical thumb and i am wanted to convert it to a hydraulic thumb. Is there a company out there and sells a turn key product? if not can i use a third function kit and run the thumb when i convert the mechanical thumb to the hyraulic? Thanks and looking forward to the comments
Hydraulic thumb for BH77
- Thread starter srchallenger
- Start date
This is just my opinion but having the same mechanical thumb on a bh92 but also having a grapple I suggest putting your money towards a grapple, you'll do 5 times the work with it.
I appreciate your thoughts and I do consider it an option. Right now I like the challenge of making the mechanical thumb a hydraulic thumb.
When you move to a hydraulic thumb there are important design considerations that are often overlooked.
On any control valve, for example a loader or a hoe, the main valve incorporates a relief valve to limit the amount of weight/force which can be lifted. This relief valve is only in the hydraulic circuit when the control lever is moved out of its neutral position. Once the control lever is back in the neutral position the hydraulic fluid is locked in the closed circuit.
An example to explain what I mean: If you use a loader to pick up a full bucket which it is just managing to lift because the relief valve is saying enough. Now you get off the tractor leaving the bucket raised and decide to shovel more material into the bucket. The relief valve is no longer in the circuit protecting the hoses, cylinders and valves. By adding more material to the bucket, the bucket and lift arm cylinders are having to support more weight and in doing so they become high pressure hydraulic pumps and expose parts of the hydraulic system to pressures which can fail components.
With a hydraulic thumb you have two hydraulic circuits forcing against each other. By virtue of the linkages involved, either the bucket or thumb will have greater leverage over the other circuit and will have the effect of greatly magnifying the hydraulic pressures in one of the circuits.
I am not an expert on hoes or excavators but have read on this and other forums of owners finding they have bent cylinders and blown hoses.
This short video by Messicks demonstrates how easy it is to over pressure a hydraulic system when existing components become pumps.
Messicks
If you want a hydraulic thumb then don't just add a cylinder to the existing mechanical thumb but find a knowledgeable company to give you a reliable installation.
Dave
On any control valve, for example a loader or a hoe, the main valve incorporates a relief valve to limit the amount of weight/force which can be lifted. This relief valve is only in the hydraulic circuit when the control lever is moved out of its neutral position. Once the control lever is back in the neutral position the hydraulic fluid is locked in the closed circuit.
An example to explain what I mean: If you use a loader to pick up a full bucket which it is just managing to lift because the relief valve is saying enough. Now you get off the tractor leaving the bucket raised and decide to shovel more material into the bucket. The relief valve is no longer in the circuit protecting the hoses, cylinders and valves. By adding more material to the bucket, the bucket and lift arm cylinders are having to support more weight and in doing so they become high pressure hydraulic pumps and expose parts of the hydraulic system to pressures which can fail components.
With a hydraulic thumb you have two hydraulic circuits forcing against each other. By virtue of the linkages involved, either the bucket or thumb will have greater leverage over the other circuit and will have the effect of greatly magnifying the hydraulic pressures in one of the circuits.
I am not an expert on hoes or excavators but have read on this and other forums of owners finding they have bent cylinders and blown hoses.
This short video by Messicks demonstrates how easy it is to over pressure a hydraulic system when existing components become pumps.
Messicks
If you want a hydraulic thumb then don't just add a cylinder to the existing mechanical thumb but find a knowledgeable company to give you a reliable installation.
Dave
Dave
Thanks for the input. Much appreciated. I think fladogman is right and better off with a grapple. I am weighing my options.
Thanks for the input. Much appreciated. I think fladogman is right and better off with a grapple. I am weighing my options.
I plan to add the kubota rear remote kit to my BX23s tlb knowing the position of the piping will need to be modified to work with the backhoe. I want to add a hydraulic cylinder on the thumb and control it through one of the remote circuits. Do I understand you, that this is potentially a problem because the potential pressure between the bucket on the backhoe and thumb pumping up the pressure in the system. Any comments on running the hoses and and other potential issue would also be appreciated.