Divorced Overdrives in a fuso.

[simonsnork]

Greetings again,

My second question for the day is about divorced Overdrives. Our merry little FG is doing just fine motoring us around the West. Only she has quite the drinking problem. For those of you who read my "dead in the water" post, you already know my fuel gauge is inoperable at the moment. Thus we are trying to fuel about every 250 miles to ensure we do not have a reenactment of the very embarrassing experience covered in my prior post. But the question of how do we get better milage keeps coming up. The simplest option I can come up with is to put in a divorced overdrive and try and change the final output to the rear axle. Of course this would only work for highway driving.
If anyone out there has seen or heard of such a modification please let me know. I'd be curious as to the cost and the long term cost savings. Diesel is affordable enough here in the US. But come Africa, our first planned destination once we are done with the build, I'd like to get more than 11mpg. (Zimbabwe is $3.15 US a liter! Granted they are an outlier.) Nonetheless, diesel isn't getting cheaper these days.

Thanks again

 

[Aussie Iron]

This is something that I looked at and could not find an overdrive box (Joey Box) that was suitable without being too large and weighty and not having to stretch the chassis by at least 50cm (20") or more.
So this is way that I went :- https://www.expeditionportal.com/forum/threads/canter-regearing.157370/ . Makes it good as you can run in high range 4WD if needed and makes low range even a little lower for crawling in the rough.

Nice picture by the way.

Dan.

 

[gait]

fuel cost and fuel consumption are related. There are other factors. But first adding an overdrive to a vehicle in which 5th gear (my FG649 is, not sure about FG637) is already an overdrive may cost more than can be recovered through reduced fuel consumption. The difference in fuel consumption between original tyres and about 8% larger diameter singles was unmeasurable over several tanks full. Too many other variables.

There may be other reasons for modifying gearing, but I doubt the costs can be recovered with fuel savings.

Our fuel price in $/100 km depends on our average speed and $/litre. Thus, while Norway had high $/litre our $/100 km was lower than most European countries. Simply because the roads wouldn't permit fast driving - average speed around 50 km/hr - so our l/100km was lower.

Our fuel cost in $/month is dependent on how far we drive each day as well as $/100 km. Our long term average is around 100km/day. More than that in a month and a tiredness overtakes us. More so with age of course. But basically its a case of finding the balance between seeing the things that are to be seen in a country and driving through it. We once conversed with a couple of cyclists and remarked how nice it must be to be moving slowly - they thought it would be nicer walking.

Distances in Zimbabwe are not that great. Victoria Falls to Beitbridge (Zambezi to Limpopo rivers), or Victoria Falls to Harare are around 700 - 800 km. A tank and a bit, or less than a tank at slower speed. Its not a big country. Take your time.

We have two 120 litre tanks. Our strategy for Zimbabwe would be to fill up in Zambia, or better still cross the Zambezi on the ferry at Kazangula (where Chobe River meets Zambezi) into Botswana and fill up (there are three fuel stations near Kasani, cheaper than Zambia). Minimise refuelling in Zimbabwe. Refuel in South Africa. Or juggle it with other countries depending on your route. If in the east and visas permit then have a day trip to Mozambique. Probably what some of the locals do.

Same for food. And cash. And so on.

Its 45 years since I drove through Zimbabwe. Nice place. Very different then. Fuel was rationed, we had more fuel coupons than we could use, and there was a healthy black market.

 

[simonsnork]

Thanks for the input.

Dan,
I'll have a good read of your mod when I'm not fighting bad cell service. It looks like the"right" way to go but might be a little complicated for these thumbs.

Gait,
Thanks for the Intel on Zimbabwe. We would be starting in the opposite corner so hopefully Mugabe's legacy will have dessipated a bit. I hear you on going slow. Your comparison made to the cyclists wishing to walk isn't always the case. In Ethiopia we were on a TVS India bike. Motorcycles were still quite novel at the time. The kids loved to through rocks at us. For that matter they liked to the anything at us. When we chatted with some pedal bikers they said it was awful. The kids would run along side them throwing rocks as they rode up hill. Then gravity would take effect and the cyclists would escape their tormenters. Only to find out the kids would flag down a lorry and get a lift to the bottom of the next hill where the entertainment would begin again.
Granted this was a unique place. Somali Land Ethiopia had many challenges.

 

[Aussie Iron]

But first adding an overdrive to a vehicle in which 5th gear (my FG649 is, not sure about FG637) is already an overdrive.

FG649 and 637/9 are the same gearbox and transfer case and you are correct in saying that we have 5th gear as overdrive in our gearboxes, But our transfer cases are then underdriven in high range. So there goes the overdrive advantage. Saving on fuel cost is real if a lot of normal road mileage is traveled.

Dan.