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Old 15 Nov 2005
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Location: Horncastle,Lincolnshire,UK
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Mercedes 917 mods

I am the proud owner of Merc 917 AF-which is a 4x4 10 tonne 170 HP thingy which has been converted into a camper truck. largely uses Unimog mechanicals i.e. 6-speed box with low ratio and permanent 4x4. Wonderful though it is, it suffers from the Unimog problem of slowness. To be more accurate it isn't exactly slow (80Km/hr) but at 80 the revs are almost at the red line of 2500 rpm. keeping in the green and I'm doing not much more than 60ks. Result very slow progress

So what I want to do is change the axle ratios. I have found out from MB that this is possible. I have 40:7 crown wheel and pinion and want to change to 43:10 but no one can tell me if it's wise. Any views?

I appreciate I may need to up the power/torque a bit and was going to fit an intercooler and re set the fuel pump. Again, any views?

I'm planning a slow West Africa trip to see friends in Mali in a year or so, so not in any particular rush but if anyone knows where I can get some cheaper CW&Ps I'd be grateful. Mercedes quote £1,000 a piece

Best wishes

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Old 16 Nov 2005
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What tyres are you running? It might be less expensive as you have to buy tyres anyway to upgrade to a 14x20 or even a 16x20.
They add that real off road look as well as lengthening the effective gearing.

Don’t forget commercial engines are designed to survive being run at max all the time so it’s more your ears (and the fuel bill) that suffer.

How annoying a slow truck is depends on attitude and itinerary. Once you’re on the back roads and pistes you rarely get to the max speed of the truck, it’s another matter crossing Spain or doing Layoune/NKT on the tar without going completely potty. The Sète – Tangier ferry is an excellent alternative for the former; for the latter it’s a matter of convincing She Who Is Too Cautious that you won’t get lost, stuck, crash, break something in the dunes, run out of whatever, etc.
Oh yes, Kayes-Bamako is also mind-numbingly boring if you take the north route.
Happy trails.

(edit) There's always the possibility of recovering road ratio CW&Ps from a scrapyard, trouble is you don't know how many KMs it's done.

[This message has been edited by Luke (edited 16 November 2005).]
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Old 20 Nov 2005
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Thanks Luke and sorry for delay in coming back to you.

"Group 4" (so called because it looks rather like a prison truck) already has 14.5 R 20 mud/sand tyres which make it look more than sufficiently macho so there's not much scope there. But it is a neat idea to increase the rolling radius. In the end though the reason why I reckoned I had to do something is that a moments inattention and you're well in the 'red'. And boy does it hammer the fuel consumtion (never likely to be G4's best selling point!) running beyond the 'green'.

I thought about trying to work on the transfer box but gave that up as both impractical and resulting in a non-standard (and thus impossible to get spares for) vehicle. So the options are sticking at 60ks or changing the axle ratios. Now 60ks is fine for off-road/piste but for tarmac here and in Europe it is a serious pain not the least for other road users.

I guess the reason why I posted this subject is that I wondered if anyone had tried this on a Unimog, though I'm not sure if the axles are exactly the same for sure. I was also interested in whether anyone had tried intercooling a Merc 6-litre diesel.

I guess this winter will be spent stripping Merc 1617 axles in my local scrap yard..........

Regards Q
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Old 21 Nov 2005
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It sounds like G4 is a good looking beastie.
I am surprised to read that it has Mog entrails, it's an Atego 4x4 isn't it?
As a forward cab it's a short bellhousing gearbox, you have to drop the box to change the clutch (not like the Mog)

Does it have portal axles? Beware of which way round the cw&p turn, it's backwards on a portal axle.

To save some heavy lifting, now might be a time to befriend/tame the parts receptionist at your local Merc Truck dealer. His parts catalog cd will have details of your axles, from there you can find other models that used the same units.
It'll give you more direction in your scrapyard challenge.

While you're at it see if you can get him to copy the CDs for you, I set off with the Iveco parts catalog installed on the PC. When you're on the phone or trying to order by email from darkest wherever, quoting a part number is so much more effective than describing the thingumy behind the wotsit next to the doofrey, to receive the wrong part by DHL.
It's usually much quicker than waiting for a part to arrive from the official dealer network in the country.

Happy axlehunting
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Old 29 Nov 2005
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Hi Luke

Sorry not to have replied before but sadly the world of work......

G4 is one generation older than an Atego. It's 1992 vintage and is apparently called something quaint like an Ecoliner (I'd never heard of one either). Basically it's the same chassis as all those Mercs the numbers of which end in '17 eg 1617. From my researches, It has the same axle internals as the on-road models, just different ratios. To be honest I'd assumed the mechanicals were the same as a Mog but you've made me think that perhaps they ain't. Just can't imagine the transfer box not being Mog though......

The suggestion of getting the parts CD is a brilliant one. Not the least being that I can spend even more hours engaging in work displacement. As it's far too cold to be getting shitted up in a scrap yard I'll be sticking with that for the moment!

What's your Iveco then? Have you done anything on the intercooler front to try and up the power/torque? And have you done anything about fuel capacity? The reason I ask is that Group 4 has a puny (for it's current fuel consumption) 150 litre tank. Trouble is there's no room to increase it without major surgery on the air tanks and battery mountings so I was wondering whether to instal a cross-chassis saddle tank between body and cab and gravity feed that back into the main tank. Thoughts?....Does anyone know who makes such things or am I looking at getting a custom one made up?

Anyway Luke thanks for your thoughts.

From the lack of posts I guess no one's intercooled a Mog!

Best wishes Q
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Old 2 Dec 2005
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Hello Quintin
The Mog gearbox and transfer case are one unit with the reduction and the reverser at the end, giving eight forward and eight reverse gears. It’s also a structural part of the suspension, being the anchor point of the huge triangular swingarm. Merc also make a bolt-on transfer case for “ordinary” 4x4 trucks. It doesn’t mage your G4 any less cool, with 14.5x20 tyres it must have an excellent attitude. Now the search for two trucks with the right CW&P will begin. With the help of the CD and a telephone you’ll root out what you need.

My Iveco’s nothing as interesting (or as high off the ground) as your G4. Mine’s a Turbo Daily 4x4 modified.
The chassis is the 5 tonne NATO reinforced with suspension to match, it runs twin wheels on the back and the camper box is 4m long, with an extra 1M50 over the cab in motorhome style.

It’s woefully underpowered, and in France where the Raid culture is king there are plenty of hop-up kits and tuners which/who propose to add up to 30% power by fiddling with my Bosch injection pump. One day I’ll do it, but only after a careful study of supplementary cooling available.
The intercooler would help that, but not by much. A TD engine already receives more than the necessary air into its cylinders (as a heating agent to set off the explosion) if the charge of air is cooler the engine runs cooler and can therefore burn more fuel. Adding an intercooler without boosting the injection doesn’t do much for the power, but helps the longevity of the engine. One of the truck rally teams would be able to point you to someone who could soup up your pump.
I don’t have air brakes, so the full length between cab and back wheels is tank. I have custom welded alu tanks simply bolted through the floor of the box with big reinforcing plates. They give me 260 l in total fine for the little engine that only consumes 15l/100km. Behind the rear wheels on one side is the original Iveco tank which serves the generator, on the other side. (It’s petrol, I want to change to diesel to get an extra 80l fuel capacity)
I’m sorry I can’t give you the name of the tank manufacturer, I bought the vehicle 2nd hand; It was made by MachZone in Hull though.

Hanging the tanks off the box is crude, but it gives more capacity than a chassis mount and reduces the vibration they see.
I’m sure you could put your air tanks on the inside of the chassis, there’s usually a lot of space between the chassis beam and the driveshafts that is badly exploited. A bit of canny plumbing is all it would take. Or perhaps behind the rear wheels.
It’s worth keeping the tanks low for stability reasons, your space between cab and box is better used to store sand ladders (less visible) or to cut a passage through.
I would recommend getting the batteries out of temptation’s way. I don’t know how your box is laid out but if there’s a bench/dinette up front just put them under that, directly above the original position (in a plastic tub). The cables could even be long enough to accommodate this, if not a welding supplies shop can sort you out with the necessary.

Taking it easy we once managed 1940 kms on tar between fill ups (the last 100 were nerve wracking) A range like that is very rarely necessary but it does allow you to be choosy about where you fill up, and to take advantage of cheap fuel when you find it.

I envy you; I’m head down at a boring job dreaming of the next escape (or how to pay for it more precisely)
Happy planning


(The length of the text is directly proportional to the boredom of the job)
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