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Restoring a big truck

By John Milliman

    With the supply of unrestored/unmolested light duty pickups dwindling rapidly, many old truck enthusiasts are turning to medium duty trucks. While sharing some similarities and methods with their light duty brothers, the bigger trucks require a modified approach to restoration.

Restoring the

big trucks


G.L. Perry's unrestored 5000-Series AD dump truckObviously when we say "big" trucks, we are, in fact, talking about "medium duty" trucks (to be accurate) in the 1 1/2 to 2-ton range. The restoration of heavy-duty vehicles (semi tractors and the like) is an entirely different endeavor and well beyond the scope of this Web site and while certainly possible, is beyond a lot of hobbyist restorers (like me!).

    My comments are written with the '47-'55 1st Series (Advance Design) trucks in mind, but will generally apply to all pre-'60 trucks. It seems that the trucks in the light duty and medium duty ranges really diverge after that.

    From my vantage point here on the Stovebolt Page, I see a lot of interest in the bigger AD trucks now. Presumably because the supply of unrestored light ADs is starting to dwindle.

    There are a lot of pre-WWII medium duty trucks being worked on, but by far, the ADs represent the largest "interest group" if you will. And, for what it's worth, of the bigger trucks, the most popular (by a wide margin) seems to be the AD COE. Guys who find a short wheelbase AD COE in good condition consider themselves blessed. Now, guys who find PREWAR COEs in RESTOREABLE CONDITION consider themselves to have found the Holy Grail!

    So, among the AD trucks, the nomenclature runs like this:

Don't try this with a 1/2-TonOverall

    Here are some general thoughts regarding the bigger trucks before we get down to specifics. This may seem patently obvious, but ... Bigger trucks are, um, bigger. They're taller, wider, longer and heavier than the pickups. This makes them more of a challenge to store, park, transport and drive. Right off the bat, one should keep in mind that unlike a pickup, most medium duty trucks will not fit in the standard garage. They may not even fit the average driveway -- important things to consider before bringing baby home! Many of the bigger truck's components require special consideration, as well.

 Multi-piece rims can be lethal if handled improperly -- BE CAREFUL!   For example, the tires and rims generally weigh around 100 lbs. each making them difficult, as well as dangerous, to deal with. And as long as we're talking about the tires and rims, the Bud wheels on the older trucks usual are two and three-piece rims. Some are even split rims. These older rim styles are dangerous, and even lethal, for somebody who is not experienced with them -- they should be left to professionals to take apart. Thus, anyone contemplating restoring a bigger truck should be aware of the increased logistics involved -- they can be quite different from those required by a light truck. Most shadetree/hobbyist tools (like floor jacks, jack stands, etc) are not capable of handling a heavy vehicle like a medium duty truck -- before attempting a restoration, one is well advised to ensure the tools at hand can handle the job.

    After the restoration is complete and the truck is ready to drive, registration and insurance will be required. Just about all of these bigger trucks were classified as commercial or farm vehicles. Although a lot of states authorize historic tags for antique commercial vehicles, it is still an issue to be researched by the individual restorer. The same goes for the drivers' licensing requirements. The cutoff for a Commercial Driver's License is 26,000 lbs. gross vehicle weight. Over 26,000 lbs. requires a CDL. It sure would stink to put a lot of time, money and effort into a truck you couldn't legally drive!

    Finally, remember the big trucks are geared low for a reason -- the ole babbitted 235 (see below) or 216 just didn't produce enough grunt to move a lot of weight so the engineers made up for that through gear reduction in the rear end. You simply will not be able to cruise on the Interstate in your antique medium-duty truck. More on this below.

Cabs interchange with lighter trucks...but not much else!Big Truck Sheet Metal

    Most big truck cabs interchange with the pickups until about 1960, making cab restoration the easiest part of the whole job. All the weather stripping kits, upholstery kits, glass and interior hardware (doorknobs, etc) is the same. Move forward of the firewall and you're out of Schlitz.

    Once you go bigger than a one-ton, the hoods, fenders, inner fenders, radiator shrouds are different (they're BIGGER!) -- mainly to accommodate the larger tires and wheels found on the bigger trucks. On a lot of 4000 and 6000-series, the radiators have been moved forward to accommodate the longer, newer engines (More on that below) when the engines were replaced. When this was done, generally, the radiator stands and shrouds were "modified" as needed -- and not with future restorers in mind! It was done for expedience, not Carlisle Gold. So, for a lot of these trucks, some of the interior engine compartment sheet metal is junk and finding good, unaltered pieces can be a challenge (Took me about 3 years!).


Is it a 235, or is it a 235?  Darn the wraskilly babbitts, anyhow!    Okay, let's talk about engines. Think they're the same, eh? NOT! Remember, prior to the post-War trucks, the engines WERE the same.

    For '47-'53 AD trucks, though, the medium trucks got the bigger 235 developed during the war. But this engine is NOT THE SAME as the later 235 that came out in '54. Oh no, this engine is not as long (That's why the radiator shroud sheet metal has been cut on trucks with a newer engine installed) and is babbitted. Oh joy!

    The good news for an owner of the average medium-duty AD truck, however, is that his original engine probably died an ugly death during the Eisenhower administration and was replaced by a full-pressure oiled 235 (The one in my truck is from a '57 Corvette, believe it or not). Or, once the babbitted 235's came out (they also made better power), bigger truck owners wisely took out their babbitted 235's and used them for a better purpose -- boat anchors.

    For the restorer wanting complete originality, my hat is off to them and I wish them bon chance in even finding one of those babbitted 235s, let alone finding someone to rebuild it. Finding mechanicals for that engine will be a quest worthy of an Arthurian Legend in itself. If strict originality is not important, the later 235s can be modified to look and fit like the earlier ones. Several parts vendors sell the kits to make the newer 235's and 261's look like the 216's that go into the light trucks, and that will do nicely for this application, too. How do you tell them apart? The older 235's look a lot like the later ones, except they have 216 visual cues (You might want to ask Barry Weeks for corroboration on this) like the Valve cover with acorn nuts, instead of fastening at the flanges like the later ones do. Also, I don't think the push rod cover surrounds the spark plugs. I've never seen one of these motors, so I can't tell you for sure.

    From '54-'62, though, Chevrolet installed the full-oil pressure 235 in the light duty trucks, as well as in the 4000 series trucks. At the same time, the 261 was available in 2-ton (6000 or C60 series) trucks and school buses. Until '58, it was an extra cost option above the standard 235.

The Muncie SM420 in repose...Transmissions

    Here, you're in luck. Just about all the big trucks from '47 to '67 had the same 4-speed manual transmission -- the venerable Muncie SM420. Because of its granny gear (for getting those heavy loads moving) and rugged construction, it had a long production life and remains popular with off-road/4x4 enthusiasts. It's also popular with the pick up guys who are installing those after-market rear-end upgrade kits that allow higher speeds. Although parts are starting to get hard to find, there are plenty of transmission specialists out there who are familiar with this transmission. COE's have some unique shifter linkages, but usually, if the truck still has its tranny, it will still have all of this, too.

    These trannies also have a plate on the side where a power take-off can be mounted. PTO's are used mainly to power hydraulic hoists (for dump trucks and grain trucks) or winches (tow trucks).

    The 5000 and 6000-series trucks also had the parking brake mounted on the back of the transmission. In this setup, the brake handle engaged a pad that acted upon a drum attached to the driveshaft right at the output from the transmission -- a much more desirable set up than the lighter trucks (where the parking brake handle is attached to the rear brake shoes via cables). A lot of bigger truck restorers like to fit this arrangement into their 4000 series trucks as it eliminates the need for new parking brake cables.

Rear Ends

    Let's clear one thing up that seems to be confusing for a lot of folks new to bigger trucks -- the 2-speed rear end will NOT give your truck a higher top speed. It gives you a lower low end to make starting heavier loads easier. In medium duty Advance Design trucks, the single-speed rear end has a gear ratio of 6:17. For comparison, the light truck rear for most of the pre-'60 trucks was a 4:11. The Advance Design 2-speed has an 8:10 "low-range" ratio and a 6:10 "high-range." Thus, if you are not going to be hauling anything with your truck, you don't gain much by switching to a 2-speed rear end.

    Also important -- If a higher top speed is desired for cruising the Interstate, merely switching to a lower ratio rear end out of a later model truck will hurt you more than help you. Remember that 235 up front? At best (when it was new) it was cranking out about 105 horsepower at 3,000 RPM -- not a whole lot of grunt there to be fooling with heavy loads and tall ratios. If more speed is desired, then you should consider updating the entire drive train, not just the rear end.

    Naturally, components like bearings, axles, differential gears and the like are going to be harder to find for these trucks than for their light-duty little brothers. But they are out there to be found by the patient searcher.


    Like everything else on these trucks, the brakes are going to be bigger to handle the heavier loads and increased braking power required. Brake shoes, wheel cylinders and whatnot are readily available from various parts sources -- just be prepared for heftier price tags. And that nifty 2-speed rear end you just brought home? Take a deep breath -- It takes four wheel cylinders (two per side) at about $100 each. And no, they're NOT the same as the fronts. Worn brake shoes are not a problem -- most any brake shop can reline them for you if the shoes themselves are in serviceable condition.

A '49 4400 cab and chassisBodies

    Most of the medium duty trucks came from the factory in the "Cab and Chassis" configuration. They had cabs (and everything in front), they just didn't have bodies (like stake beds, bulk fuel tanks, van boxes, etc) installed. GM, like other truck manufacturers, was not resourced to be able to outfit trucks to meet every demand, so they left that up to the customer for the most part. GM did offer a few basic bodies, the most popular being the platform stake. Because of the construction and usually hard use experienced by these trucks, original factory beds are exceptionally rare these days. Good luck finding one!

    Other trucks, mainly the 6000 series, were manufactured as "cowl and chassis." This arrangement was then shipped to a bus body manufacturer like Wayne Bus Body, in Wayne, In., where school Bus bodies were fitted to the truck.

    Usually, though, these older medium duty trucks sport a wide variety of professionally manufactured bodies, as well as an amazing array of locally produced custom bodies. A lot of trucks even received hand-me-down bodies from older trucks whose mechanical components wore out before their bodies did. This opens up a world of possibilities for the restorer of medium duty trucks who can, unlike his light duty truck-restoring compadre, mount just about anything that fits and have it be no less correct than any other truck in its class.


    To recap, the methods, skills and procedures used to restore a medium duty truck will differ very little from those of the light truck. As well, the cab sheet metal (cab, doors and interior) interchange with the light trucks up to the late '50's. Beyond that, the two diverge to varying degree. Parts can be much harder to find, components harder to handle and informational resources nearly non-existent. But, bigger trucks tend to be altered less and so they are more complete when found. They may not be as desirable as daily drivers, but the big truck restorer will derive as much satisfaction and enjoyment from his or her labors as the light truck, and will ultimately end up with a truck that's rarer (relatively speaking) and every bit as collectable.

    Just remember -- restoring a bigger truck is not for the feint of heart, weak of arm or small of garage.

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