2010 - Volume #34, Issue #1, Page #04
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Go-Anywhere Post Driver
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"In low gear it goes so slow you can hardly see the wheels move, but it will climb anything the wheels can get footing on," he says. "I've used it in places I wouldn't take a 4-WD tractor. The only way I could improve it is to put tractor treads on the wheels."
Once he gets to the general area, he can precisely maneuver into position thanks to the two front axles he used and the separate hydraulic cylinders on each set of tie rods.
He can turn both sets of wheels in the same direction and crab steer on the diagonal or turn front and back axles in opposite directions to make extremely tight turns. He can also steer with either front or back axles and let the other trail.
At the job site, the post driver can be adjusted across a 90 degree arc from the front of the vehicle to the immediate left. Once roughly in the right place, Marah can fine tune positioning by telescoping the post driver mount away from the vehicle as needed, or tip the post driver at an angle to match the slope he's on. Everything is powered hydraulically, which is why Marah spent plenty on hydraulics for the rig.
"When I sat down and figured out how I wanted this thing to work, I knew I wanted all-new hydraulics for it," says Marah. "I totaled up all the cylinders, hoses, motors and valves and told my wife I was going to max out her credit card when I ordered it all. I figure I have about $3,000 in it, of which $2,500 is for hydraulics. Other than welding rod, everything else came out of the junk pile."
The frame for the wagon is from an old trailer house. The engine is from an old Hercules air compressor, the breather is from a Massey Ferguson combine and the radiator is from a Plymouth Voyager. The front and rear running gears, transfer case and transmission are from 1950's and 1960's IH trucks. The rear axle was flipped upside down to reverse the ring gear so both axles would go in the same direction.
The Shaver post driver is a tractor 3-pt. mount, which Marah modified significantly. He moved the down pressure spring from the rear to the sides, added supports and a weight box, and mounted it inside a pipe framework so he could lift it up to accommodate up to 10-ft posts. Military surplus gas cans serve as a fuel tank and, cut open, also serve as toolboxes.
One of the biggest challenges was figuring out the hydraulic flow. The 20 hp, 4-cyl. Hercules engine, combined with the 14-gal. hydraulic pump, meant there was no hydraulic pressure to spare. Marah knew the post driver had to be the last valve in the line, as the out-flow had to be larger than in-flow to accommodate the release of the weighted head. The larger out-flow hose had to return to the reservoir. The other problem was steering, which required a very low flow.
"The first valve directed hydraulic flow to the drive; the second went to auxiliary hydraulics on the rear," explains Marah. "The next valves in the line are for steering, but ahead of them, I had to put a flow control valve and an excess fluid bypass."
Once past the steering valves, the steering and the excess lines rejoin, and full pressure is directed to the post driver portion of the vehicle. Here again the flow is directed through a series of valves, including the cylinder that moves the driver from the left side of the rig to the front as it extends. This required a 1/4 round steel base for it to ride on.
"I figured out how big an arc I would need and drew a chalk line on the floor of my shop," recalls Marah. "I got out equal lengths of 3/16-in. thick, 4-in. angle iron and made a cut every 8 to 10 in. in one face and bent the other face away from the cut. What I ended up with was 8 to 10 flat faces rather than a true arc."
Marah then welded in bits of metal to fill the gaps that had opened. The welded face became the lip the post driver mount arm traveled on, while the uncut face became the base.
"I knew the base needed to be stronger, and I knew it would take a lot of beating from the driver," he says.
The arm itself is a length of 4-in. steel tubing with a 3 1/2 in. length inside it to provide telescoping action, thanks to yet another cylinder. Marah mounted L-shape brackets on the 4-in. tubing that hook under the lip of the arc. While the weight of the driver helps hold it down, the brackets help take some of the torque off the hinge pins that attach the post driver tower to the arm. A third cylinder/valve mounted a few feet above the telescoping arm and attached to the driver tower adjusts pitch.
Another cylinder raises and lowers the post driver head. Marah modified the head with a box that he filled with punch-out chunks of metal.
"The added weight makes the post driver act like a dead blow hammer, delivering its full force to the post," says Marah. "However, attaching the box required moving the down pressure springs to the side. This increases the risk to anyone standing near should they break, which they do. I slipped pvc pipe over them to contain them, which it has when they have broken."
Marah also added an emergency brake to the transmission to lock the wheels up.
The post-driving rig has worked very well for Marah for about 6 years. He does acknowledge one change he would make if redoing it. "I would put in a larger hydraulic pump and a larger motor on the ground drive," he says. "That would increase ground speed significantly. As it is, if I am going very far, I load it on a trailer and haul it."
Contact: FARM SHOW Followup, Larry Marah, 6885 Marsh Rd., Norwood, Mo. 65717 (ph 417 746 4129).
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