IH 1800 truck

These techniques are not difficult to learn. But it does take a bit of practice to get it right.

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The purpose of the aux 3 speed is to divide or “split” each relatively widely spaced gear on the main transmission into 3 more closely spaced gears. When properly shifted this keeps the engine RPM very near the engine’s maximum power point as the truck accelerates. This then gives the best acceleration for a heavily loaded truck. It also eliminates low RPM lugging strain on the engine – though at the expense of increased ‘strain’ on the operator(!)

Like Rusty suggests simply leave the aux 3 speed in OD and shift just the 5 speed. Only with the truck loaded do you really need to use the aux.

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A good video of an experienced driver float shifting twin stick being can be found at the link below.

• shifting a 5 & 3

And after learning to run that (also a couple ancient Macks with 5+3 and 5+4 boxes) I found learning to shift the “modern” air-shifted 8LL, 10, 13 and 15 speed Roadrangers etc.is a snap.

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Incidentally an old timer sagely shared this when I was learning the twin stick: If you get lost in the gears you might just as well open the door, step outside and enjoy a smoke while you let everything coast to a stop. Then put ‘er in low-low and "start back up the stairs” all over again.

Aside from the smoking part the old guy wasn't too far off....(!)

jimmy