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January 15, 2016

Twiddling the Twin Stick

David McNeill executes the through-the-wheel compound shift
that allows a shift in the main transmission and the auxiliary
at almost the same time,  
Now here’s one for you old truck lovers: a Bubblenose Kenworth with a two-stick 4x4 Spicer transmission. Driven by David McNeill, the video shows his skill shifting the main and auxiliary transmission in this 1955 Kenworth 523 cabover with Small Cam 350 Cummins power.

The video shows him tiptoeing the old Bullnose out from his Louisiana field where the most amazing assortment of trucking history is quietly rusting away. The camera shows the progression of the shifting of this two-stick, with the “round-the-houses” shift pattern of the auxiliary and the first compound shift of one to two in the main transmission and back to second gear in the auxiliary. And watch his left leg: after getting under way, he leaves the clutch well alone through all the shifts, as one should with this transmission setup.

I remember the time I drove a two-stick Pete 359 back in 1986 – 30 years ago! I picked up the new truck with a 6 and 4 from what was Engs Peterbilt in Pico Rivera, California. I also tiptoed, out of the dealership and around the corner and parked the truck. Then I got the transmission manuals out of the glovebox and armed with a pocket calculator, worked out the ratios for each gear position of the six ratios in the main transmission and four in the auxiliary – a total of 24 gear pairs.

The auxiliary had four ratios that included two under-drives (a granny low and regular underdrive ratios), a direct and an overdrive. In most cases, the granny low combination gear position in one gear of the main transmission was approximately the same ratio as the overdrive in the previous gear.

So in starting out when coupled to my loaded trailer, the sequence was to select first in the main transmission and first in the auxiliary. Next was a shift straight back to second in the auxiliary, third was over to the companion slot in the aux and fourth was up toward the dash, all the while in the auxiliary trans.

The next shift was the compound, grabbing second gear in the main box and second in the aux. This has to be completed in a strict sequence because you never want to have two neutrals at the same time as you’ll never find a gear.

This Pete 359 featured a six and four. I had to calculate
the gear ratio pairs to know how to shift it.
So the main trans is shifted to second, then immediately the aux is shifted back to second. Old hands like David McMcNeill in the video did this by slipping the left arm through the steering wheel to work the main shift lever, using the right hand to grab the auxiliary. I contented myself with using just the right hand but getting through the shift as quickly as possible.

On a grade like the Grapevine heading out of Los Angeles going north, when doing a compound upshift I found going for the first gear in the aux while upshifting the main gave me around the same ratio I’d just left, which was OK as the speed had rolled off during the shift.

Great care had to be taken on the downgrade side heading for Bakersfield as it is steep and goes down for about 10 miles. Just the place not to be caught with two neutrals and no gear to be found! My old test route then headed over Tehachapi to Mojave, doing it all again, then south to the starting point at the Ontario, California, TA truckstop.

That Pete was a terrific truck, really comfortable but with the over-stiff front suspension that was a feature of Petes back then. It became over-excited on I-10’s concrete surfaces, making it impossible to hold, let alone drink, a cup of coffee. But even so, the experience was amazing.

Shifting the transmissions has proven an enduring memory, especially against the background of today’s automated manual Eaton Ultrashift and Volvo iShift transmissions. With these, you sit back and let the truck decide what gear it wants and take itself there. Better, probably, safer, for sure. But memorable? Not so much ...

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