(first posted 5/7/2017) We’ve had plenty of love here for the Chevrolet and GMC “Advanced Design” (1948-1955) pickups and trucks, but we’ve never properly worshiped this particular long-nose version of the medium-duty GMC, with its free-standing fenders and protruding front end, like this Model 620 stakebed shot and posted at the Cohort by tbm3fan. In case you’re wondering why it has that longer front end, it’s to make room for the biggest GMC straight six gas engine ever, the “360” and “426”.
The 400 and 620 series trucks covered the wide range called “medium duty”, for operators wanting something less than a full-blown HD truck, but still able to haul quite heavy loads, up to 32,000 GVW, and 50,000 GCV (with trailer).
The legendary “Army Workhorse” ohv gas six had proven itself in WW2 in countless military trucks and vehicles, and was a staple of the GMC truck line. It was available in the 400 series in 248 and 270 cu.in size, although starting in 1952, the ultimate 302 cu.on version was also available.
But for the higher speeds and heavier loads increasingly called for in the post-war era, GMC also developed a larger line of six cylinder gas engines, and that required more room under the hood. The two versions available in the 620 series were the “360”, with 360.8 cu.in and 155 gross hp, and the “426”, with 177 gross hp. There was also a 503 cu.in version available either later, or in the even larger HD models (900 series).
This one sports a “2TON 52” tag; that would make it at the low end of the weight range available, although those “ton” ratings were always a bit vague.
Not the sharpest picture of the interior, and for that matter, it’s not really all that different from a pickup, except for the five speed Clark transmission.
Sure is a fine looking truck, and the moan of that big Jimmy six working a load is undoubtedly a treat for the ears. We’ll just have to use our imaginations.
Nice piece of iron! I sold GMC’s from 1981 until 1995. GMC would only put in the Detroit Diesel, which was made by the subsidiary of GM. However, when the purchasing agent of Hess oil demanded Cummins Diesels in his GMC order in, I think, 1979, GM came to the party. That opened the door for alternate Diesel power in GMC heavy-duty trucks. The GMC Truck & Bus Group was a small enough division that we, as sales people, were able to contact manufacturing and engineering people directly to resolve problems. It was terrific.
GMC did offer other manufacturer’s engines in their trucks.
The Top Kick medium duties were powered by Cat 3208 engines, don’t recall any other engine used in the Top Kick.
The Heavy line up of Astro, Brigadier and General had Cats and Cummins power besides the usual DD engines.
The truck lines had great sway back then when buying trucks
It was simple, they wanted this engine, this transmission and this rear axle. If the manufacturer didn’t offer it they weren’t in the running for the sale. I believe International didn’t originally offer the DD 60 Series in their trucks, when one of their large customer bought a competitor’s truck IH changed their tune.
Volvo did drop all Cat engines around 1997, rumor was Volvo didn’t like buying engines from the competition, Volvo construction equipment vs Cat construction equipment.
Emissions regulations and consolidation in the truck manufacturing business slimmed things up and moved towards more vertical integration.
Odd GMC’s I worked on over the years.
Astro with a 903 V8 Cummins, special frame rails up front, the 903 was a wide engine.
Brigadiers with Cat 3406 and Spicer dual countershaft transmissions.
Two GMC medium duty trucks with Deutz 6 cyl air cooled diesels. These were conversions done to brand new trucks, done locally, originally had 427 engines. I believe this was some “covert” operation by the regional GMC field office that was co-located with us. The 427’s sat out back at the loading dock for years.
The P-Chassis under a step-van body powered by Cummins B 4 cyl engines. I recall these for the goofy power steering pump drive.
Another odd one was a convoluted mess. GMC had repossessed a bunch of GMC chassis’, These were front engine chassis’, no bodies. Well our local megalopolis thought it was a to good of a deal to pass up so they bought two of these chassis’ for garbage trucks. Then the morons put out a bid to have a cab and hood installed and made functional before it would go to have a garbage compactor body installed. The spec was very tight, spelling out what gauges were required, all items that were required and functioning. However the big loop hole was it didn’t specify what body had to be used. The next piece is the IH dealer right across the street, they bid and using an S series IH cab. They won the bid and built this Frankenstein truck. The only reason I knew of it was when it showed up in my bay for some repair work. It was in for a power steering leak. I was totally unaware of what was instore for me until I flipped the hood open. This looks awfully familiar. It was a GMC chassis? It had the typical GMC truck power steering leak, to small P/S reservoir and bad return line design. The return oil was coming in the side of the tank, tank was only 4-5″ wide. The oil shot straight across the tank impacting the other side and roiling up the oil. The cure was drilling out the fitting a bit, inserting a very short piece of soft copper tubing bent at about a 45 degree angle and soldered in place. This directed the oil down, greatly reducing the turbulence and you now had a happy customer.
The mechanic world at that time was kind of close, you probably knew someone who new someone that could get you the information you needed. I knew people at the said government this truck belonged to. I called that night and asked about this truck. He responded, oh yea, we have to of those morphydites, its an embarrassing story, want to here it?
I have never been that well versed in medium duty trucks and find that monster of a six just fabulous.
Nice ~
I hope it doesn’t get scrapped like most older rigs this size .
-Nate
This splendid beast deserves a good home with the understanding that she stays as is. She don’t need no facelift. Just love the patina.
At home with the other ghosts of the past at the more or less ghost town of the old (Alameda?) Naval Air Station. Nice article, and literature shots.
It is Alameda.
I recognized it immediately. You can see the bay bridge in the background.
You can actually see the truck in Googles overhead shot on Monarch St. Yes, many ghosts at the base including the Grey Ghost.
A buddy of mine just picked up a fire truck one of those. can’t wait to get up there and see if we can get it to pump.
Interesting to see these had a PCV system to scavenge crankcase fumes in a decade when competitive engines still used road draft tubes. Big advantage for trucks customarily driven at low speed where a road draft tube is minimally effective. GMCs would have less sludge buildup with such a system even if oil change intervals were extended. Probably a selling point for a fleet operator.
Wonderful photos! Even though GMC called these “medium-duty,” some time as best as I can recall, by the 1960’s trucks in The U.S. were given class ratings. Anything over 33,000 GVW (gross vehicle weight) rating is a Class 8 truck and, therefore, heavy-duty. Even medium-duty trucks built by manufacturers become heavy-duty Class 8 models when they have tandem rear axles because the lowest ratings for the axles are a 10,000-pound front axle and a 34,000-pound rear axle. These trucks on the medium-duty chassis use lighter duty engines than heavy-duty models. Thus, they are less costly and, of course, less durable. For many applications, however, the medium-duty cab-and-chassis is all that is needed, such as 6-yard dump trucks (tippers? in Europe), van bodies and the like. It is a poor choice for a highway tractor because of the stress here of fast speeds and at the same time hilly terrain.
During the 1930’s, the large displacement six cylinder GMC truck engines were further developments of the Buick big sixes last used in passeenger cars for the 1930 model year. Those last, largest Buick Series 60 engines were 331.4 cu.in. OHV. Whether any of these postwar engines were still of that series, I defer to experts in GMC engines.
CC Effect on steroids. I saw this nice 630 Series Jimmy at the first truck show of the season just this morning, although this one ran 6-71 diesel power.
That red one to it’s right and behind it is a big 900 Series.
SIXTY CUBIC INCHES PER PISTON??? But wait 426/6= a freakin’ 71 cubes just bouncing up and down inside that sleeve. The mind boggles. Of course, when I hear ‘302’, ‘360’ and ‘426’, I think of late 60s muscle iron.
I bet those are fun to drive at around 45-50 mph.
I am envisioning (6) 1-liter soda bottles lined up in a row. That is the small engine in this truck. Wow!
GMC introduced their own all-new 6 cylinder engines in 1939, comprising of 3 different series. The smallest were used in light and medium duty trucks, and ranged from 228 to 302 cubic inches. These engines were similar in some respects to the OHV Buick engines GMC used previously. The ‘Family 2’ engines were built in 308 and 318 cubic inch displacements. I don’t know much about these, they seemed to have been somewhat redundant and were dropped in 1950. I believe they were closer in design to the larger GMC 6’s than the ‘Family 1’ engines. The largest (save for the pre-war 707) was the ‘Family 3’ large OHV 6’s. These went from 360 to 502 cubic inches, had 2 piece engine blocks (cylinder block was bolted to a separate crankcase casting) and had the intake and exhaust manifolds on the right side, unusual for a GM straight 6. They were renowned for their power and stamina and gave decent fuel economy compared to competitive engines of the day, most of which were very large flathead 6’s like the White Mustang and Mack Magnadyne. Both the Family 1 and 3 engines had a long production run and lasted until 1959, when they were both replaced by the GMC V-6 engines. Interesting design objective of the V-6’s was that they were to replace all light, medium, and heavy duty gasoline engines in GMC’s model lineup with one common engine family. And sire a medium duty diesel as well!
Bob, thank you for the detailed explanation. That’s how I roughly remembered it, but I’d forgotten about the Family 2 engines. Yes, it was quite a design brief for the V6; what a huge spectrum to cover.
A 426 (or possibly a 502) in an old wrecker in the process of being restored that I’ve been seeing around for a few years. Note the line of nuts directly behind the generator that mark the connection between the block and the crankcase as referenced in Bob’s comment.
The semi-scabby old wrecker in question….
Wow, look at that row of restored yellow Macks! Some guy must be loaded….
That’s Skip McKean. Owns an oil and propane distribution company. Really down to earth kind of guy and a class act. Trucks are a 1942 ED, 1946 EH, 1951 LF and a B61. All are gas motored except the B61.
Speaking of big sixes, the ’51 LF runs a 510. It’s far from the biggest one Mack made. That would be their 707.
Skip’s fleet makes quite an entrance at a show. Please try to ignore the annoying kid with the harmonica in the audio…
You’ll see that at plenty of ATHS Shows. A well to do collector will have 10-15+ historical trucks all in the same livery.
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CC Effect strikes again! Saw a 630 Series fire truck parking in a front yard yesterday! Didn’t stop to take a pic tho, next time I see it I will.
The old factory ad above with the two blue trucks shows both of them sporting only one puny rear view mirror. I’m glad I wasn’t driving back then. Curiously the ad says “The New GMC six Wheelers”, but the trucks shown are 10 wheelers.
I had one of those old GMC’s, I think it was a ’54, a former volunteer fire department truck. I got the truck in the mid 80s planning on building a nice wrecker for my lot. Plans were aborted when some sonofa!!!!!!! stole the GMC from my yard and it was never recovered. Oh well…. such is life.
Doing restoration on this model and need a flywheel, Missing teeth
Sadly this truck in now gone but as to what fate I don’t know unless hiding somewhere else on the base.
Found the truck on google maps. Looks like it is now parked in front of “Dashe Cellars” Hope someone does something with it