(first posted 2/7/2014. It’s Memorial Day in the US, and in honor of all the men and women who gave their lives in service to this country, let’s take another ride in one of the most significant tools of WWII)
Maybe you found your way to CC because you were sick of all those infantile “We Drive The World’s Fastest Cars” 200+ mph shoot-outs or such on endless glossy magazine covers. No, we’re strictly grown ups here, and confine ourselves to erudite discussions of historical minutia and debating alternative business plans that would undoubtedly have catapulted Packard into being the world’s largest luxury car manufacturer today. But we all have our moments of weakness, as when I was confronted with this offer: “Hey Paul, you want to take a ride in my GMC CCKW, and see what she’ll do, wide open?” Did you have to ask?
When I need certain heavy-duty mechanical jobs done, like the clutch replaced in my truck, I head to Jeff’s Garage. But since that happens very rarely, I sometimes just drop in and see what his latest toy is. Jeff’s taste mirrors mine: older original vehicles with plenty of patina and used regularly; for a long time, his daily driver was his 1936 Plymouth, which he even let me drive (CC here).
Jeff’s latest ride is a wee bit younger than that, but decidedly gnarlier. And since he welcomes any opportunity to take it out for a spin, he invited me along. Actually, he offered to let me drive it too, but I decided that making a video of him working the old Jimmy through the gears up to top speed might be be easier on the seventy-year-old non-synchronized gears, as well as his ears. Although I suspect its crash-box transmission has seen some tough grinds in its long life.
image credit: wwiivehicles.com
Of the three WWII 2.5 ton 6×6 trucks (GMC, Studebaker, International), the GMC “Jimmy” was built in the greatest numbers by far, undoubtedly due to GM’s huge production capacity. Over half a million were built for the Army and the Lend-Lease program, and they were most famously employed in the Red Ball Express, the vast supply line that served the advancing Allied troops marching east after the Normandy invasion. At its peak, almost 6,000 vehicles were on that road daily, from the port at Antwerp to the front lines. The Jimmy acquitted itself superbly, cementing its place in history.
Initially, all CCKWs had closed cabs, as used on civilian GMC trucks of the time. But presumably to save on precious steel, later version also came in a simple open cab, with folding windshield and canvas top. Even in the bed, wood eventually substituted steel. These trucks came in two wheelbase lengths (145″, 164″) and were used in a wide range of duties, with an equally wide range of beds.
Jeff’s truck is an open-cab version that has had a closed-cab kit attached. The dump bed is not original; this truck worked for many years as a gravel hauler for a back-woods logging operation. Jeff plans to put an open bed on the back, something like it would likely have had originally.
The attachment bolts for the upper half of the cab are clearly visible. Nice “opera window” on the back, although that hardly makes this a Brougham. Every square inch of this truck is solid steel and patina, with a dash of glass and rubber thrown in for good measure.
Let’s check out the rest of this truck before we hop in. One of the most obvious things is that it’s only got single wheels on the back. That’s because the prior owners put larger size tires on it (9.00×20), instead of the original 7.50x20s. Jeff has a lead on some original sized rubber, and already has someone to take the dump bed and put it to use on an old Ford (not mine!). But there’s plenty of times I’d wished I had a dump truck like this.
The other thing that’s instantly noticeable is the rear axle differential housing, which has its main ring gear oriented longitudinal, like vintage Fords. CCKWs came with two types of rear axles; Timken split axles (which is what these are) or the GMC banjo type axles, that look like typical modern axles and were considered the stronger of the two.
But that’s not nearly as different from more modern trucks than how the drive to the two rear axles is arranged. Instead of one drive shaft feeding both axles, there’s two; with the one heading to the rear-most axle having an intermediate rest stop on top of its more forward companion.
Here’s the rear output of the transfer case, with a parking brake on the shaft on the left, which feeds the rear-most axle. The other one is a bit below on the right. I wonder if there’s some intrinsic advantage, like redundancy if one drive shaft or axle craps out? These trucks were known to be nigh-near un-killable.
For all you lovers of undercarriages, shafts and universal joints, here’s that transfer case from the front.
And the front axle, of course; which appears to have a reinforcing bar.
Before we fire her up, let’s pay our respects to that winch. I wonder what stories it could unwind for us.
There’s the legendary GMC 270 CID (4416 cc) OHV six, rated at 91.5 hp in this application. The GMC six was built in two main versions, a low deck (236 and 248 CID), commonly used in pickups and light trucks from 1939 up to about 1960. The raised deck block came in 256. 270 and 302 CID versions; the 302 being particularly desirable due its phenomenal torque.
That’s not to say these Jimmys couldn’t make gobs of horsepower either; they were one of the most commonly used engines in hot rods, dirt track and Bonneville racers, and even sports cars with six Amal carbs , as well as six swept exhaust pipes thanks to an aftermarket cylinder head. Their performance heyday overlapped with the Ford flathead V8 — which it was quite capable of spanking too — from the late 30s up to about 1955 or so, when OHV V8s became plentiful, especially the Chevy. Can you imagine what this one sounds like at full chat?
Here’s a quick warm-up, literally, to our main drive, as Jeff starts up the Jimmy and pulls forward a bit. Jeff has a lead on a 302, which he’s thinking of rebuilding and dropping into his CCKW. The 302, in conjunction with the four-speed Hydramatic (with two ranges), was used in the CCKW’s successor, the M135.
Now let’s hop in and get ready for our drive. The cab is a very spartan affair, not surprisingly, and mighty cozy too.
Instrumentation is complete, in terms of the usual vital statistics.
The CCKW has a five speed manual, with direct gear being fourth, and an overdrive fifth. The two-speed transfer case gives a wide range of speeds based on the maximum engine speed of 2750 rpm, from a wall-climbing 2 mph to 45. As the chart says, that’s based on it being equipped with the 7.50×20 tires, and this one has oversize 9.00x20s, so the speeds in gears will actually be a bit higher; 2.3 mph in low-low?
The shift pattern is a bit hard to make out on the plate, but it’s not exactly what we’re used to in modern cars. Second (typical starting gear) is at the top left; then down for third; then over and down for fourth, then straight up for fifth. Reverse is on the far right top, and first is below that.
We drove a couple of miles out West 18th to blow out its cobwebs, and started rolling video just as Jeff turned the Jimmy around to head back into town. Jeff said that the tired 270 six would probably benefit from a good tune-up or even a re-build, but it chuffs right along. The speedometer is way out of whack, at least in part due to the larger tires. I’m guessing we managed to get up to around 45 or so; it certainly felt at least that fast or more, due to the noise. The ride is of course stiff and bouncy, but not quite as bad as I might have expected. The CCKW’s 2.5 ton load rating was very conservative, and it was commonly doubled in real world (war) use.
And what is the very first car we encounter and follow as we get back to Curbsidelandia? A Mercedes W116 S-Class from the seventies. We tried to catch it, but I’m afraid the Jimmy wasn’t quite up to it, even if the Benz was a diesel 300SD. If the Jimmy had a warmed-over 302 with five carbs, it would have been a different story.
Jeff is in love with his new big toy, which means some of his other projects are languishing. But that’s how it is with serial automotive monogamists, and this one is certainly lovable as well as drivable. And I’ve been invited to retest it when the 302 goes in. It should blow right through fifty then.