BH77 - has anyone considered converting mechanical thumb to hydraulic?

[broncorm]

Subscribing
I've wanted to do this since I got the tractor with manual thumb

 

[CDN Farm Boy]

I did also find a place that would do customer cylinders for not too outrageous prices - so in my mind the last big hurdle to mentally work out is the figuring out the exact right valve to use to control the thing.

Why the custom cyl? I'm using a 2" x 10" from Princess Auto and it works just fine. While I had to do slight (easy) mods to the mounting tubes, the main (expensive) parts of the cyl are still intact.

 

[ameador1]

Subscribing to this thread...

I have a Mahindra 3535 with manual thumb and thinking about modifying this to hydraulic. The info in this thread has been helpful in understanding the concerns to think about and the kinds of options to consider. Thanks for posting all this great stuff!

 

[Sysop]

Old thread, not a lot of action to subscribe to. No comments since Christmas '13.

 

[ameador1]

Old thread, not a lot of action to subscribe to. No comments since Christmas '13.

Yeah I know, but subscribing adds it to my 'subscribed threads' list - some good info in this thread. If I don't subscribe to it now, I'll never find it when I want it again...

Do you have the hydraulic details figured out on our models? As far as what lines to use, type of control units, etc...? If you have that stuff already worked out, then looking at my thumb may be the last piece of the puzzle. I figure at some point I will do this with mine - probably not until next year at best, but I want to understand this stuff better in any case. Research early you know... But hey, if you get around to checking out my setup and know how to work out the details, then maybe sooner

I think... I (you too?) have an aux hydraulic connection back there - sounds like that would help make the conversion easier.

 

[bumperm]

I'm in the wait-and-see crowd. Been using the manual thumb (which is truly amazing for plucking whole sage brush!), but do intend to go hydraulic.

I may have a partial answer for one of the concerns previously mentioned, and that is the issue of having the bucket curl, when it comes up against the thumb, over pressure the backhoe or tractor hydraulics upstream when it acts as the master cylinder. A pilot controlled check valve, installed at the thumb cylinder will lock the cylinder, isolating the cylinder hydraulics until the thumb control valve is activated. This doesn't stop the thumb cylinder itself from being "overpressured", but I see this as less of a problem or issue.

When building the top and tilt for my 3-point, the top cylinder (from SurplusSales) already came with DPCV, I added a single PCV to the tilt cylinder to solve the "creep down" issue.

bumper

 

[Sysop]

The hydraulics typically used on these backhoes for the thumb is just a diverter valve plumbed into (I think) the curl function, with a footswitch control.

 

[bumperm]

Sysop, going with a diverter has appeal (fairly simple), but the downside is one cannot have both the thumb and curl closing or opening at the same time, as one's thumb and index finger would. Also, the deck on my BH77 doesn't offer much foot room to add a switch, though I'm sure it can be done.

In any case, there are other options, especially if the tractor already has additional rear hydraulic function valves, or an additional spool can be added to the hoe's valves (not likely with the BH77). In my case, I have rear hydraulic valves for top and tilt as well as a joystick electric controlled 3rd function valve for the loader. The latter could easily be used for the thumb by running the hydraulic lines back to the hoe and by paralleling the two buttons on the loader joy stick.

bumper

 

[ameador1]

Yeah, I can see how having the bucket and thumb move at the same time would be nice. Moving logs around would have been extra nice being able to do it that way. But I suppose if only one at a time were able to move, it would just be a little more work. Not too much of a big deal. I assume the diverter mentioned is like a selector? You choose path A or path B for the hydraulic fluid to flow, so you would either be controlling the bucket, or the thumb? So, the pedal moved one way would be path A, and moved the other would be path B? If so, what if it is in the middle? Do you get 50% to both paths?

 

[Sysop]

Actually in most instances you don't operate both at once on these smaller units with less hydraulic flow. You either set the bucket against the item and pin it with the thumb, or vice versa. Most I have seen operate their backhoes no differently than if they had a mechanical thumb. But being able to adjust the thumb from the operator's seat versus climbing down and adjusting pins is well worth the investment for many.

 

[ameador1]

That's more or less what I do. I'm curious, and will have to look, but wonder if the thumb could be pushed out further with a hydraulic arm than with the fixed arm? One of the problems I have is grabbing smaller logs where it can be difficult to grab them without the bucket catching dirt. If the thumb could be pushed out further to meet the bucket (well, log actually) that would help - so probably not as much of having them move in tandem as much as getting a little further thumb grab. I think that would take some study - to get the right length hydraulic piston to get the thumb to close up well, yet extend out as far as possible.

 

[Sysop]

I think the geometry of the factory kits stays the same and has roughly the same range of motion. Without knowing the size and stroke of the piston that will be used, there isn't much way of figuring it.

 

[dfkrug]

Yeah, I can see how having the bucket and thumb move at the same time would be nice.
Moving logs around would have been extra nice being able to do it that way. But I suppose if only one at a time were
able to move, it would just be a little more work. Not too much of a big deal.

It is a big deal for me. May not be for some others. I have had it both ways.

I move rocks and logs, and my hyd thumb setup has more than 150 hours on it. So I prefer a "true grapple" setup,
where both thumb and bkt can move at the same time and the one with least resistance moves. If I
lock my thumb and try to grasp a heavy rock using only the bkt curl up against the stationary thumb, the curl
forces often pull the tractor rather than grab the rock. With logs, it moves the log before I grasp it.

I used a single parallel diverter spool valve tied to the base of the bkt curl cyl to achieve this:
http://www.tractorbynet.com/forums/build-yourself/125912-custom-hydraulic-backhoe-thumb.html

A manual spool valve can be feathered to do this, but the usual 2-spool solenoid diverter can not.
By "feathered", I mean that you can send pressure to both curl and thumb by partially opening the
upstream curl valve while opening the downstream manual thumb valve simultaneously.

 

[CDN Farm Boy]

..... I think that would take some study - to get the right length hydraulic piston to get the thumb to close up well, yet extend out as far as possible.

Since you already have a mechanical thumb, it shouldn't take more than a minute with a tape measure to figure out the required length.
With the thumb fully retracted, measure pin to pin for the closed cyl length. Disconnect your mechanical linkage and move the thumb out as far as you can prior to the body of the yet to be purchased cyl contacts the stick and measure the pin distance again. Now you have your extended length.

It took me longer to type this than it did to measure mine

My BH77 perfectly fit a standard length cyl and gave me more travel than the factory mechanical link

 

[CDN Farm Boy]

Duplicate post deleted

 

[bumperm]

My BH77 perfectly fit a standard length cyl and gave me more travel than the factory mechanical link

Have you already done this upgrade? If so, would please provide more details? Which cylinder did you use, did you use a diverter or a separate valve? Foot switch or?

Thanks much,

bumper

 

[CDN Farm Boy]

Have you already done this upgrade? If so, would please provide more details? Which cylinder did you use, did you use a diverter or a separate valve? Foot switch or?

Thanks much,

bumper

Yup, did it last summer. For the money I have in it, I couldn't be happier.

http://www.tractorbynet.com/forums/customization/287591-mechanical-thumb-conversion-hydraulic.html

The basics are also listed in post # 84 of this thread

 

[Monster5601]

Yup, did it last summer. For the money I have in it, I couldn't be happier.

http://www.tractorbynet.com/forums/customization/287591-mechanical-thumb-conversion-hydraulic.html

The basics are also listed in post # 84 of this thread

I'm a hydraulic know-not-much outside of knowing how to spell hydraulic.

Could I use a 1 1/2 bore cylinder instead of a 2 inch?

I have a BH76 on my B3030 with two optional rear remotes, one will be used for the thumb.

 

[bumperm]

I'm a hydraulic know-not-much outside of knowing how to spell hydraulic.

Could I use a 1 1/2 bore cylinder instead of a 2 inch?

I have a BH76 on my B3030 with two optional rear remotes, one will be used for the thumb.

There is a potential problem going with a smaller cylinder. When the bucket curls up against the thumb the mechanical force tends to move the thumb's cylinder, this in turn can generate high pressure within the thumb cylinder and downstream that can exceed the working pressure of the tractor, potentially causing damage. The amount of this pressure is based on both the ratio of bucket curl cylinder to thumb cylinder piston size - the smaller thumb cylinder will generate greater pressure, and any mechanical linkage advantage between the bucket curl and thumb - haven't looked to figure that part out. But, the take home is that the smaller thumb cylinder may or may not work. However, going to a smaller cylinder does potentially move things in the wrong direction considering that a 2" cylinder has been shown to work.

If there is over pressure, and the thumb controlling valve is closed, any damage should be limited to thumb cylinder and associated hose and valve, if the valve is open, then the tractor's relief valve should open and dump the excess pressure . . . this is all a WAG on my part, as I too don't know that much about hydraulics.

bumper

 

[CDN Farm Boy]

Aside from what bumperm said, I went with the 2" cyl primarily for fitment reasons. I knew what retracted and extended lengths I had to work with. The other main factor was the mounting pins of the mechanical are 1" and I didn't want to have to modify them.

From the Princess Auto catalog I was looking at, 1" pins automatically put me at a 2" cyl as the 1.5" used 3/4" pins and the 2.5" cyl used 1 1/8". The mounting boss on the cyl base was the right width but I had to turn it 90° for port clearance and narrow the rod end. It has about 1/4" of travel left at full retraction when the thumb contacts the body of the cyl. I don't think I could have ordered it any closer.

It is much also closer to the 2.5" bucket cyl to lessen the overpowering chances and also has a much larger rod to resist bending.