Progress in July:
The team at Mil-Spec Vehicle Restoration has made significant progress on several fronts with our CCKW 353 Fuel Truck this past month. The once tired-looking frame now appears virtually brand new and is beginning to resemble a truck once again!
This month saw the team focus on installing the remaining differential unit and the pillow block before hooking up all of the drive shafts. They also fabricated and installed new brake lines, refurbished the carburetor, distributor, and steering box, while also cleaning and sealing the fuel tank.
Front Differential, Drive Shafts & Wheel Hubs:
The Mil-Spec team completed their overhaul of the final differential unit for the Fuel Truck, this being for the front axle. Its rebuild involved a similar level of effort to the differentials in the rear and intermediate axles covered in the previous restoration update. The newly-rebuilt front differential is now installed on the Fuel Truck, as are the fully-refurbished drive shafts (and their associated universal joints) linking each of the differentials to the vehicle's transfer case.
A reprise view of the CCKW maintenance manual schematic showing the layout for the vehicle's drive train.
The freshly refurbished and reinstalled front axle differential. Note that the drive shaft and its associated universal joint have been similarly overhauled, repainted and reinstalled. (image via Mil-Spec)
The freshly-overhauled, repainted and reinstalled drive shafts for the rear and intermediate axles. This image shows where they each connect to the transfer case (via a universal joint) with the shaft at the center of the image driving the rear axle. The large grey component mounted to the frame at the top of the image includes the main components for the Hydrovac brake-boosting system. (image via Mil-Spec)
The rear wheel hubs received new brake shoes and freshly-rebuilt axles (with brand new bearing races) - as seen here. (image via Mil-Spec)
Brakes:
Mil-Spec continued to fabricate and install new stainless steel brake lines around the Fuel Truck's frame over the past month. As part of this process, they replaced the damaged tee-fitting which links the hydrovac unit to the brake master cylinder (which was itself also replaced). For those unfamiliar, the hydrovac magnifies a vehicle's braking power so that a driver need only exert a small amount of force on the brake pedal to effect significantly greater hydraulic pressure on the brake drums. Heavily-laden CCKW trucks, with gross operating weights up to and even exceeding 20,000lbs, needed this ingenious device (developed by Bendix during the 1930s) to enable their safe operation. Updated variants of this same hydrovac design are in widespread use even to this day. For those wishing to learn more, there is a marvelous WWII-vintage military training film explaining the system HERE.
New stainless steel brake lines going in around the front end of the chassis. Note also, the refurbished and freshly-reinstalled front differential at the lower center of the image. (image via Mil-Spec)
The damaged brake line tee-fitting for the Hydrovac system which needed replacing. (image via Mil-Spec)
Freshly installed stainless steel brake lines going in on the chassis. Note the brand new tee-fitting is clipped to the frame in its purpose-built bracket, ready for connecting to the Hydrovac brake-booster. (image via Mil-Spec)
The recently-installed gray-painted Hydrovac brake-boosting system is seen here mounted against the righthand chassis frame in this image. (image via Mil-Spec)
Distributor:
The distributor is an essential element in an engine's ignition system. It 'distributes' a high-voltage electrical impulse to the spark plug in each engine cylinder, triggering a spark (and thus combustion) in a precisely timed sequence. For the Fuel Truck's GMC 270 straight-six, this sequence runs with the following cylinder order (1-5-3-6-2-4) to ensure both efficient combustion and a smooth-running engine.
The distributor which came with our Fuel Truck was in rough condition. After disassembling it, the Mil-Spec team found the inner workings to be worn beyond economical repair. As a result, they cannibalized a New Old Stock (NOS) example to find replacement parts for the points, condenser, breaker plate, shaft, advance weights and springs needed to rebuild the original unit. Media-blasting the distributor housing's exterior to remove old coatings and surface corrosion, they repainted it and added a new data plate, suitably stamped with the appropriate model and serial numbers used on the original. The now fully-restored distributor awaits installation on the Fuel Truck's engine, which is presently undergoing overhaul.
An older image depicting the distributor in place on the Fuel Truck's engine prior to overhaul. (image via Mil-Spec)
A circuit diagram from the CCKW's maintenance manual depicting the engine's ignition system, and how the distributor feeds each of the six spark plug lines (one per cylinder, numbered 1 through 6).
A New Old Stock distributor, seen here in its original box, provided some of its internal parts to refurbish the unit for the Fuel Truck. (image via Mil-Spec)
The fully-refurbished distributor (sans cap) ready for reinstallation on the engine once that is also overhauled. The gear near the bottom is used to synchronize the position of the rotary arm (shrouded within the black housing) with the correct electrical circuit at precisely the right time a spark plug needs to fire. (image via Mil-Spec)
Carburetor:
The carburetor is another key engine component. When tuned correctly, it ensures that a precise mixture of fuel and air arrives in each cylinder so proper combustion can occur. While rough-looking in appearance externally, the carburetor which came with our Fuel Truck project remained in restorable condition. The team disassembled the unit, cleaned and inspected its parts, while also media-blasting and repainting the housing. During reassembly, they also adjusted the carburetor's float to make sure it would allow the appropriate level of fuel through to the engine (similarly to the way a float in a toilet cistern governs the level of water per flush). The now fully-refurbished carburetor also features a brand new set of gaskets, custom-fabricated in Mil-Spec's workshop.
A view of the Fuel Truck before disassembly began in earnest earlier this year. The vehicle's carburetor (with the air filter housing atop it) is shown where it sits on the engine. The team at Mil-Spec recently fully refurbished both of these items. (image via Mil-Spec)
This figure, culled from page 202 of the CCKW Maintenance Manual (TM9-801), depicts the carburetor (with the large round air filter housing on top) mounted to the vehicle's engine.
The Fuel Truck's fully overhauled carburetor following its refurbishment. The silver-toned cylinder at the top is where the air filter housing attaches. The latter unit has already been overhauled and is in storage awaiting installation. (image via Mil-Spec)
Steering Box:
The steering box is a small device attached to the base of the steering column which translates the driver's rotational input to the steering wheel into the pivoting action which guides the direction of the vehicle's front wheels.
Mil-Spec's team disassembled the steering box, then cleaned and inspected the parts. They had to replace the worn-out upper and lower bearings, fabricate new gaskets for the seals, and adjust the lower bearing pre-load and sector shaft back lash (to minimize the slop in the steering action). They then reassembled the unit, making sure to safety-wire the side-cover retaining bolts (to prevent them working loose after longterm use).
An illustration from the CCKW's maintenance manual which roughly describes the steering layout. The steering box at the lower end of the steering column translates the driver's rotational input on the steering wheel into a lateral movement which pivots the drag links connected to the front wheels, adjusting their direction.
An illustration revealing the inner workings of the steering box. Note the ball bearing race around the worm screw's thread which eases the rotation of the steering column while moving the toothed rack which houses it up or down. The rack, in turn, engages with a pinion gear which adjusts the angle of the pivot arm (more properly referred to as a Pitman arm) at the far right of the image. The Pitman arm, in turn, positions the drag link controlling the direction of the front wheels.
The steering column on the work bench with the steering box housing removed to reveal the worm screw and its associated steering rack. While it may be a little difficult to visualize, the heavy-gauged worm screw on the column translates rotary motion into linear motion on the rack which is clamped around it. The teeth on this block (just visible on its underside) mesh with a pinion gear which, via a series of drag links, will adjust the direction of the vehicle's front wheels. Note the newly-fabricated gaskets on the workbench as well. (image via Mil-Spec)
While there is a lot of clutter in this image, the refurbished steering column and its associated steering box are visible here in the foreground. The end cap of the steering box has yet to be installed at this point, its mating surface masked off in tape for the painting process. Note the CCKW's restored gearbox can be seen at the back of the workbench. (image via Mil-Spec)
A view of the fully refurbished steering box, attached to the steering column which is resting on the CCKW's chassis frame awaiting installation. (image via Mil-Spec)