Featured here is a mid 1980's White Volvo Expeditor. It is what is known as a 'low cab forward' model. These are popular in urban applications where the driver must frequently get in and out of the truck. The classic application is for garbage collection. Indeed this particular truck spent its first life as a city refuse truck with a Lodal body on it. The truck outlasted the body and found its way to our collection.
This particular model in its day contained a Lodal body designed to pick up dumpsters with a set of forks and flip them over the cab and dump them into the top of the body. What a mess. Even after removing the garbage packer body, I have pressure washed the truck a couple of times and it still has garbage in it. It is a particular mess behind the cab. Most of us don't think of refuse as being heavy, but obviously it is and this truck was built for the heaviest weights. It features a double steel frame, 12x22.25 tires on the back, and a 20,000 lb front axle. The engine is a Cat 3306B, presumably set around 270 HP. The transmission is an Allsion HT750DRD. This is a 5 speed automatic with a deep reduction first gear. Although there is some reason to believe it is a retrofit, the truck has an air throttle, and the transmission shift modulator is air controlled tapped right off the throttle.
As with any cabover, the doghouse dominates inside. Things are really cramped inside. There is barely space for the brake pedal and the throttle between the steering column and the doghouse. Indeed the brake valve is under the steering column and there is a weird offset pedal that reaches around the steering column. The wiring, and breaker box are all jammed in under and around the dash board, in a most crammed manner. The shifter is conveniently located on top of the doghouse. Since this is an older style Allison, it controls the transmission with a shifter cable. Indeed this transmission is very similar to the CLBT750 found in the Oskhosh M911 featured elsewhere on this site. The C models when in off highway applications and the HT models went into highway trucks. I"m told the differences are in the valve body that handles the shift logic. Indeed they do shift differently. The Oshkosh is always wanting to shift into second gear and won't stay in first unless you hold the shifter in that position. First in the 750DRD is a lock in shift and unless you like real lurches you will stop the truck before shifting out of first. In normal driving conditions, first is never used.
If there was ever an application for a cabover truck, surely, the refuse truck is the candidate. The refuse truck needs to be big and heavy, yet nible enough to be at home in every urban back alley. It has to be able to find its way to every dumpster where are always stuck in a corner somewhere. A cabover configuration helps implement the need for 10 lbs in a 5 lb. bag design. The next thing that doesn't make it in this application is the 'Freightliner' cabover design which placed the cab and the drivers door directly over the front wheel implicitly requiring the driver to bound straight up 4 feet to get into the drivers seat. This was possibly tolerable in the linehaul context, but certainly not acceptable in a truck that stops at every garbage can. The low cab forward design moves the cab forward and down. This places the operator in front of the front tire---sitting on the wheel well. It is still not as low as one would like, but you can reach the steering wheel from the ground and only one runningboard step is required. (In more recent years and even 'lower' cabforward model has been made in which the whole cab has been moved forward of the front axle. This allows the cab to be set as low as one would like.) In this model, the floorboard is just above the frame level, and the seat is on top of the wheel well which implies a lot less climbing than in a highway cabover in which your feet are above the front wheel, but you are still up there a ways, and the space is cramped as you are sitting on the front tire with your feet in a hole in front of the fender in the space beside the engine.
As far as service is concerned, The cab easily tilts forward with a hydraulic system in many ways allowing better access than you can get on a conventional truck. The cab tilts far enough that you can walk between the front tire and the back of the bumper and belly right up to the engine on either side. The back of the engine and the transmission are behind the cab. What you don't get with one of these trucks is a 'clean cab axle'. While the 4 air tanks are all stuffed inside the frame over the tandems, there are all kinds of rubbish that have to be mounted behind the cab, including the air cleaner, muffler, battery box, fuel tank, air dryer (if any) and even the power steering reservoir, and the water filter. Lodal managed to get the front of the garbage packer body up to within a couple feet of the back of the cab, then they hung the fuel tank, batteries and air dryer under their body.
In my reworking of the truck so as to make a forestry fire truck out of it I put a 14 foot long water tank on it----8 feet forward of the center of the tandems and 6 feet back. This left me with about 6 feet of space between the cab and the front of the tank for various things such as the Christmas tree and the hose reel, and even the PTO pump. The Allison transmission has a PTO access point high on the left side, so the pump is mounted above the transmission inside the frame. I actually made a bracket that bolted to the transmission on which to mount the pump which is connected to the PTO via a short drive line. This way the alignment of the PTO shaft will never change een when the frame twists or the motor mounts shift. Of course I did install flexible hoses to connect the pump to the rest of the vehicle.
The shifting of a PTO can be a special issue with an automatic transmission. The classic PTO shifter is a manual contraption---either an overgrown cable with a 'big red knob' or a lever. These manual shifts contemplate that you will step on the clutch before engaging the PTO. With a manual transmission that is sort of second nature, but with an Automatic, the problem is the same, but there is no clutch, yet you must stop the transmission from turning before sliding the gears together. If you are using a manual shift PTO on an automatic transmission the trick is to put the vehicle in gear at an idle thus stalling the converter---and stopping the transmission. Then you can make the shift. Fortunately, however, Chelsea has a better solution---a power shift PTO. Instead of sliding a spur gear into the cluster gear as is done with a manual shift PTO, the gear is always engaged, and then there is a clutch inside the pto unit to engage the PTO. They are often air controlled but on this particular truck the PTO is electric over hydraulic. Hydrualic pressure is picked up on the transmission port used for the transmission pressure gauge. The oil goes to an electric solenoid and then to the PTO clutch. Waste oil pressure lubricates the PTO bearings. Consequently the PTO can be started or stopped regardless of rotation concerns with a dashboard switch anytime the transmission has operating pressure which should be anytime the engine is running. Actually pretty nifty.
As I understand it these 'on the fly' shifting PTO's may be installed on manual transmissions as well, but usually are not because of the expense.
PTO capacity is an issue on conventional fire trucks, but is not an issue with forestry fire trucks as they use much smaller pumps. The PTO pump on this truck is an 80 GPM Edwards positive displacement pump which by spec requires a total of 14.2 HP at its rated 1800 RPM. Their current model pump is Bronze and stainless steel so that it can pump fire retardants and foam as well as water if required. A larger model is described is some more detail at Ford Louisville Fire Truck. One of the good things about a positive displacement pump is that it will provide pressure at any speed. It moves around 40 GPM at 1000 RPM, and the volume fall off is only around 10 GPM from zero pressure to full rated pressure (200 PSI). The performance is similar at 1800 RPM---though there it is dropping from 80 GPM to 70 GPM in its working pressure range. This means that you can get full pressure with the truck idling (as long as you aren't exhausting more water than the pump is pumping. This is particularly a good thing if you have to lay a lot of hose to get to your project. You can get the pressure without roaring the engine, which is significant since forest fire management often involves laying a lot of hose and using misting sprays over a long period of time.
Requirements provide for 500 feet of hose of which 250 feet is connected and ready to use. Commonly this requirement is met with 250 feet of 1" rubber hose on a reel with another 250 feet of 1 1/2" 'canvass type' hose rolled up and carried in the truck.
I say "Canvass type", because in the good old days it was made of canvass and some of that hose is still around, but the preferred is of a synthetic design which is much improved because it doesn't rot. The real canvass hose is only good for about 1 fire because if you don't get it dried out carefully it rots, and a rotten canvass hose is worthless.
One of the real frustrations of provisioning a fire truck has to do with connecting the hose. There is utter chaos in the world when it comes to fire hose connections. Besides several sizes of hose, there are at least 4 connector types to be found. There are threaded connectors using pipe threads,and threaded connectors using 'National Fire' threads. There are Cam locks and twist locks. Thirty years ago, the State of Oregon at least used pipe threads on the 1" and National Fire on the 1 1/2". More recently the trend has been to use twist locks because the federal government went that route because the federal fire fighters couldn't figure out which end of the hose to run down the hill with, and the twist lock works either end to.
With all this confusion in mind I built a manifold (or Christmas tree as I call it) with a connector for everyone. It has pipe, National fire, and Twist lock all in 1 1/2" all available. Additionally, it has 4 hoses connected, one being a fill line, and the other 3 being one inch pipe connections: 1 to the 250 foot 'fire code reel', one to a 100 foot live reel mounted on the back of the truck, and a third to 30 feet of hose that is just tossed in a pile on the truck----this is the one to be used for equipment washing.
The second thing we have done with this truck is to install a gas drive pump on it. This is plumbed in parallel to the PTO drive pump so it can be used to provide additional water into the manifold which might be an issue if numerous hoses were in use from the truck, or if need to fill the truck, it can be removed and carried to a water supply which can then be pumped back to the truck.