Careers & Training, Features, Video

Engaging the diff locks when climbing Cunningham’s Gap

In this video, award-winning driver trainer Bill Manton discusses how to engage the power divider – or diff locks – when ascending Cunningham’s Gap.

The instalment below is part of a series of videos designed to help truck drivers navigate the steep ascent and descent of Cunningham’s Gap on the Cunningham Highway in Queensland.

They’ve been produced by the Department of Transport and Main Roads (TMR), in partnership with the Queensland Trucking Association (QTA).

From behind the wheel of a Wickham Freightlines’ Kenworth, with a Euro V Cummins engine, Manton takes to the Gap, with TMR’s principal program advisor for the South Coast region, Nicholas Lancashire, in the passenger seat.

Manton talks through what the diff locks do, before setting off. “It locks two differentials together, so one axle is driving on the front and one axle is driving on the back,” he explained.

Cunningham’s Gap is well known for its very steep grades, which are actually steeper than Toowoomba range.

“It does get up around that 14 per cent at the very last peak, where a lot of the transport guys have a bit of trouble there. But the key thing is to be prepared before you get there,” said Manton.

“Change down gears before you get there, have your diff locks in and keep your high RPM, so using your horsepower rather than the load, so you’re not changing gears half way up the last pitch.”

Lancashire added, “TMR is aware of the heavy vehicles and the time it will take to climb up the hill. We know that some heavy vehicles will have to crawl up the hill and that’s a slow process.

“But we’ll be allowing enough time for that cycling effect, for a truck to crawl up the hill safely and reach the top.

“We don’t need people to rush, we don’t need people to force their way up gears, they can pick a low gear and just safely climb up the hill – and there will be enough time to climb to the top before either the traffic signals or the traffic controller releases traffic on the top of the mountain.”


  1. Having experienced the fun of climbing The Gap in the 1980’s in a Scania I knew I’d reached the highest climb when the Horton fan bellowed that it was getting a bit hot for the engine but other than that I experienced no real problems doing the climb.
    What I do think is the problem for many doing the climb are the Eaton Fuller 18 speed gearboxes that I had found to be a nuisance when climbing steep Ranges in FN Qld for them dropping into angel gear when splitting into lower gears whereas the road ranger crash boxes were an absolute dream on any incline where I changed gears without the clutch just by the sound of the engine .
    Give me a 9 or 10 or 13 speed road ranger and I will traverse and road in any condition and climb any jump up you point me at in any combination for I know I can put my trust in that gearbox to do what I want to make my trip stress free .

    1. What are you talking about, Eaton Fuller, road ranger, call it what you like it’s one and the same gearbox.

  2. I was always taught to never split a gear going up or down steep hills back in the 70s/80s only had 250hp /290hp back then i worked for western haulage 73-84

  3. I myself in the 80s and mid 90s moving Victorians migranting to sunny Queensland 🌞 in my 1425 Benz’s single drive 10 speed road ranger travelling the hwy 39 newell melb to Brisbane. Great combination no drama both Cummingham cap 0r Toowoomba range climbing up or down in the same gear just a sweet box . 😀 treat both with respect 🙏🫡

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