One of the most useful mods I’ve made to the Harbor Freight Backhoe Trencher is adding a mechanical thumb. For around $150, this simple upgrade has transformed the machine, making it more useful for clearing brush, moving small logs, and even handling some fairly heavy rocks.
Available here ➡️ Backhoe Thumb Excavator Bolt On Universal Claw Tractor Attachment (3.25" Boom Width)
The Thumb Kit
I ordered a universal backhoe thumb from Amazon. It’s designed to fit any boom up to 3.25 inches wide and came as a simple kit (though without instructions).
The main body piece slides onto the boom from the inside, and a mounting plate goes on the outside. Two bolts pass through the outside plate and into the body, and two more secure it from the inside. Once tightened, the assembly clamps firmly onto the boom.
At first, I ran the setup exactly like this. Over time, though, the mount began to creep downward. Once I was confident in its position, I welded the mounting plate directly to the boom. That fixed the problem for good.
Attaching the Thumb
With the body in place, the thumb itself attaches with a large pivot bolt. A brace piece then connects the thumb to the boom:
- The narrow side of the brace mounts up top with a short pin.
- The longer side goes on the bottom with a long pin.
- Each pin has two hole options, which let you adjust the resting angle of the thumb.
Experimenting with these hole positions helps you find the angle that works best for the jobs you’ll be doing.
Switching to Dig Mode
To move the thumb out of the way, remove the brace piece and use the large pivot pin to lock the thumb back against the boom.