Viewed here is a larger old technology excavator. It is identifiable as 'old technology' for a number of reasons. First note that it has 'flat pad' tracks. These are nice street pads that you can drive around on asphalt ok, but unlike the more modern designs the pads are simply pinned together.
There are no separate rails or hardened pins and bushings. This design is left over from the 'block and skid steering days. This sort of undercarriage was more or less standard on the cable shovels of yesteryear. These tracks are reasonably good as supporting great weight, but very wear out quickly if the machine is driven around a lot. Of course the old block and skid steered shovels weren't driven around much to that was fine. I call them block and skid because they were generally propelled by a mechanical shaft down through the center bearing. Some where there was a disconnect on one track. When you wanted to steer, you stopped the machine, disengaged the track that released and then drove the other track either forwards or backwards as might be appropriate. If the brake didn't hold properly on the disengaged track the oiler (helper) would need to place a block of wood in front of the track (hence block and skid).
The drive train is a couple of jumps more modern than the HOPTO 900A because at least it doesn't have bevel gears and a chain drive, but it is close. The American features a conventional hydraulic motor and a gear box with a self setting brake and a lot of gear reduction. In this picture the undercarriage is actually turned backwards so you can see the gearbox on the front of the machine on the outside of the carbody. The drive sprocket rides on a splined shaft that sticks through 2 bearings and into the gearbox. There are 2 rocker pedals on the floorboard of the cab and you drive this machine with the 2 pedals, rocking them forward or backward as is appropriate.
|Pipe gallery above spool valves.|
Another thing that sets this apart from the newer machines is the low pressure hydraulics. They operate at around 2000 lbs pressure instead of 4-5000 lbs pressure. The lower pressure hydraulic systems are 'cheap keepers' in that they use cheaper pumps and are much less sensitive to dirt into the system. Indeed if you are looking for a used machine, the lower pressure systems are the ones to look for because they are repairable. Conventional wisdom is that the high pressure systems should be scrapped when the first set of pumps wears out because the pump failure will contaminate the hydraulic system with steel cuttings which can never be properly purged which will 'short life' replacement pumps causing further contamination, etc.
The problem with the low pressure system is that it must move huge oil volumes requiring large plumbing and large cylinders. After all it only takes half as much oil to do the same work if the pressure is doubled. The controls on this machine are fully mechanical with 2 long wobble sticks in the cab connected to aircraft type cables running to the spool valves. This contrast with the slightly newer American 35A log loader featured among our log loaders, which has swizzle stick controls which activate pilot valves which can be pushed around with 2 fingers but which lack the 'feel' of the 3 foot long wobble sticks. The manual activation has the advantage of precise control but the leverman has to earn his keep.
Actually this machine used a combination of cables and just plain old levers. The swing was actually controlled by an 'on demand' pump with a direction lever on it. A control cable went over to the pump to operate the direction lever. A cable was also used for the bucket control as it was a 'left/right' on the right hand wobble stick. The other controls for the excavator, including the boom, and arm were push pull on the wobble sticks. Each track had a rocker foot pedal for a drive and rabbit gear likewise had a lever on each side of the seat for the respective tracks. They were spring loaded, so to drive in rabbit gear you held both pedals engaged with your feet and held both tracks in rabbit gear by holding the levers back. Rabbit gear was physically accomplished with a couple of valves which cross fed the 'return oil' from one track into the feed for the other track. By double feeding the oil you got some more speed, but not a lot of power, so practically speaking rabbit gear wasn't used a lot.
|An aftermarket modification|
A final and unusual feature of this machine (for a backhoe) is the elevated cab. This machine which is powered by a Detroit Diesel 6V71T actually spent much of its life as a log loader. As an excavator the cabs are usually mounted low because you are digging holes with the machine and there is no need for the operative to be up high, but when used as a log loader, the elevated cab is crucial so the operator can see the top of the load of logs.
The elevated cabs are a nuisance, however, when you have to haul the machine because they are over height and have to be removed, tilted or lowered to protect the low bridges from disaster (not to mention the low wires). I am uncertain just how deep this machine will dig but machines of this size typically dig 25-30 feet deep. Though similar in weight and horsepower to the Hopto 900a, the machine behaves much differently in practice. The geometry of the boom is much different. The Hopto boom is mounted admidships right over the center of pivot. The Hopto has both a 'speed and power' position on the boom and on the dipper, and a very strong bucket rollup. It is configured to operate inside of shoring and will drop about 20 feet straight down inside of shoring and dig in a very short distance. The operator is well forward and can almost look down the hole. This is wonderful if you are working in a shored trench but perhaps no asset if you are doing some of the many other things that excavators do today. You are usually not much interested in looking 20 feet straight down while sitting in the seat of your favorite excavator if it is NOT a shored trench.
By contrast, the American has the boom mounted on the front of the mainframe and the base of the boom cylinders are out in front of the house on extensions. The overall boom length is similar to that of the Hopto, but the reach is greater. The forward position of the boom allows for a much shorter house greatly reducing the 'tail sweep'. The trade off is a larger counterweight, but it is worth it. The Hopto is built very close to the ground (The bottom of the house is less than 3 feet off the ground), but the very long house sticks behind even the ends of the tracks some distance. This creates a constant problem of swatting things with the back of the house while swinging. The dings in the back of the house attest to how many times it has swatted something. Not a pretty sight really.
The photo on the right shows the cab support system as modified for an elevated cab. This was a fairly high class modification. On earlier machines they just elevated the cab, but this put the machine overheight for transport so you had to have a crane around to actually remove the cab for transport. With the modification you see there, there is a hydaulic cylinder in the center under the cab. It lowered the cab (but not the seat or the controls). Very complex and made the cab a bit shaky, but the best that could be done with manual controls. The Japanese generation all went to hydrualic operated spool valves with nothing but small hoses going to the joysticks. This was consistent with tilt cabs, so now all you see on elevated cab models is a set of hinges for tilting the cab forward 90 degrees to lower it.
The controls are about as different as they could be. The Hopto uses hand levers for the travel. The American uses foot pedals. The Hopto has foot pedals for the bucket and swing function, while the American has everything built into the hand levers. You see it takes 4 functions to run a backhoe--The boom, dipper, bucket and swing. With the Hopto, if you can operate your hands and feet in a coordinated manner, you have something for everything.-- 2 pedals for each foot and a lever for each hand. The American solution is multi function levers. They run the boom and the dipper when moved forward and backward and the bucket and the swing when moved left and right. Either approach seems to work reasonably well, but it takes a little brain reprogramming when moving from one machine to the others. Imagine if every brand of car had the brake, and the steering wheel in a different place. Sheesh! These things are like resetting the clock in your car radio.
If you are trying to figure out which one to buy, don't bother unless you have an old machine in mind, because so far as I know neither are manufactured anymore. The excavator market has gone the way of transistor radios, and nearly all are now made in Japan, and indeed there are far more brands of excavators and manufacturers. Many an excavator comes to the US with a primer paint job and is 'branded' here. This doesn't mean that they are exactly the same though, as carbodies, booms and counterweights are often different.
The American manufacturers completely flubbed the excavator market. The Excavator is now the single most popular piece of construction equipment, but unfortunately, the U.S. manufacturers were sleeping and nearly every 'shovel company' --the logical ancestor of the excavator, failed to make the transition from cable controlled shovels to hydraulic excavators.
As originally designed, but not maintained, this machine had a telescoping (Expando) undercarriage. It had provision for sliding the tracks in and out about a foot on each side. In the wide position the track gauge was about 10 feet (as measured to the center of the track) and is about 8 feet in the narrowed position. The wider stance provides additional stability over the side, and the narrower position simplifies transport. This machine has grown permanently in the narrow position while the 35a loader has grown permanently in the wide position. This machine fits reasonably on our General Trailer lowboy which is 10 feet wide but the existence of the wide gauge model has us building outriggers for the lowboy so we can widen the deck to 12 feet.
Just a short word here about the Company that made this thing. American Hoist and Derrick Co was an old line heavy iron manufacturing company dating back to 1881 based in Saint Paul, Minnisota. It's St. Paul manufacturing plant closed in March, 1985, however it was a diversified corporation which including such things as the Coast-toCoast Hardware. The Corporate name changed to Amdura, and the Construction equipment division was sold off and eventually taken private under the name of American Crane Corp. and is still in business. although they don't make excavators. Ultimately they became part of Terex
which is has collected a wide variety of heavy equipment companies.
American is best known for its cranes, though back in the days when the company flourished (as in before hydraulics stood the construction machinery market on its ear) the basic unit for a shovel, backhoe, dragline, clam, crane etc. was all the same. with just different booms.
If you are old enough to have gray hair, we recall when names like American, Koehring, P & H, Link Belt, Bantum, and Bucyrus-Erie were all names in this business. Now they are all either gone or marginalized. Hydraulic cranes have taken all but the longest reach market, shovels have disappeared except in the largest mining applications, and excavators either bear the brand name of some Japanese city (as in Kobelco) or are made there and marketed with domestic names (Link-Belt and Cat come to mind).
|Detroit Diesel 6V-71T|
There comes a day. We got the front one for a parts machine, and the back one is the one you see with the excavator front on it above. The tracks are shot and out of production and everything else is iffy so the excavator front went to the 35A which was down graded to a rock loader, and these two sit here awaiting my ambition to cut them up for scrap. There should be 30 tons or so of scrap here at prices ranging from $180 to $280 dollars a ton depending on grade so we won't come out too badly.
The counterweights are cast iron and weigh 16,000 lbs as compared to the fabricated boxes now in fashion that are full of concrete or sand.The design of these old shovels is fundamentally different than what you find with the newer Japanese models which often have a deck with components bolted to them. Behind the rotec this machine has simply two fabricated frame rails running to the back of the machine. The engine and pump assembly is completely self contained and sits on its own subframe and is bolted down to the main frame. Clear to the back is a heavy plate that is welding and braced to the back of the frame rails. The 16,000 lb counterweight was bolted to that with 2 large bolts. The two large spool valves are in front of the engine on the cab side so the control levers will function and on the left side is the fuel tank and oil tank. The swing motor assembly and swivel valve are in the center of the machine.
The engine is a Detroit 6V71T mounted completely self contained on its own set of skids. The pumps are conventional gear pumps with multiple segments. A manual disconnect clutch is provided for starting if it is necessary to start the engine without the pumps engaged. An oil radiator is provided in front of the engine radiator. The subframe is bolted down with 10 5/8" bolts to the main frame.