MB 917 vs 1120/1124?

[mog]

I'm going to toss into the mix, fire truck vs. not a fire truck, regardless of whether a 917 vs 1120/1124 as I have some direct comparisons. My '79 1017AF has a sweet spot cruise speed of 100 kph (fast axles with 395/85-20s) while my friends 1017A (ex-Bundeswehr) on 395/85-20 even with an upgraded larger turbo, added intercooler, larger injectors, and a 'tweeted' fuel pump has a sweet spot of 90 kph. In addition, we both pulls 'hills' at pretty much the same speed. Certainly, his engine (OM352A) has more power, but I feel the axle ratio makes a bigger difference in cruising. Also, a consideration is (only direct knowledge of the 1017 series), if you have lockers, (rear, front, or both) then the drivetrain is a full-time four-wheel drive even in 'road mode', while with no lockers then it is two-wheel drive in 'road mode', with the front axle disconnected. As mine has no lockers, I was able to add AVM locking hubs to the front axle, which helped with less driveline drag (maybe .4-.6 km/l better).

I'll add that my German friend who was a mechanical engineer for M.A.N. trucks in Switzerland has a 1995 MB1120 for his around the Western Hemisphere trip. I asked him why a Mercedes over a M.A.N., and why a 1995 year truck. He feels that Mercedes has much better worldwide support over M.A.N., and he bought a 1995 as that was the last year of 'mechanical controls', which he wanted for reliability and simplicity.

 

[Neil]

if you have lockers, (rear, front, or both) then the drivetrain is a full-time four-wheel drive even in 'road mode', while with no lockers then it is two-wheel drive in 'road mode', with the front axle disconnected.

Not quite correct , if I have read that right.

My 1017a has a rear diff lock only and is two wheel drive high range in road mode and four wheel drive low range in offroad mode.

I too can fit free wheeling hubs on the front but i doubt they would gain 4 to 6 km per litre . This is almost a 100 % gain. Double the distance. I travelled for many months with an identical 1017a as mine. He had free wheling hubs and our fuel consumption difference was negligable.

Forgive me if a have read it wrong

Neil

 

[mog]

Not quite correct , if I have read that right.
My 1017a has a rear diff lock only and is two wheel drive high range in road mode and four wheel drive low range in offroad mode.

This is out of the 'Operating Instructions' for the 1017,1217,1417,1617 (PN#380 584 01 96)

perhaps our 1017s have different transfer cases?

I too can fit free wheeling hubs on the front but i doubt they would gain 4 to 6 km per litre . This is almost a 100 % gain. Double the distance. I travelled for many months with an identical 1017a as mine. He had free wheling hubs and our fuel consumption difference was negligable.
Forgive me if a have read it wrong
Neil

It is easy to miss but that is point 4 to point 6 km/l. So in 'American' 1 to 1.5 mpg better. Or in my case a 7-10% improvement.

 

[Neil]

Yes I missed the decimal point, my mistake. Sorry

When buying my 1017 i looked at maybe a couple of hundred in various German military auctions via VEBEG .
All were the same. 2 or 4wd with rear diff lock.

I have seen , and travelled with a permanent 4wd 1017a. It had front and rear Diff locks, completely different axles to mine, It had portal axles.

My transfer box is marked with

750.5. VG 500. 3/W

Neil

 

[Geo.Lander]

OK, questions.. I am really confused, some overspill in this thread from my build thread too..

• How do i know if i have fast or slow axles? (FRONT AXLE, RATIO 39:8, REAR AXLE, RATIO 43:10)?
• The discussion over permanent 4x4 or 4x2 (4x4 then engaged with the low range transfer case) is still very unclear, can someone please shed some light on this?

 

[Neil]

With regard to the 2 or 4wd

If the model number has an A in it such as 1017A or 917 AF , this states that vehicle has 4wd.

what it doesn't tell us is if the 4wd is permanent or switchable from 2wd to 4wd.

it would appear that there is no hard or fast rule. Mercedes made several variations in each model.

for example my 1017 came in switchable 2wd to 4wd. It also came with either a rear difflock or both front and rear difflock.

So unfortunately its really hard to confidently identify what the vehicle has simply by the model number.

Its also means there is no so easy to tell even if you see the vehicle. For example the pneumatic dial shown a couple of pages back on a permanent 4wd model might simple select a high range and a low range and a neutral. Whereas on my vehicle, the exact same dial not only selects high and low range but at the same time selects 2 or 4wd

I know this doesn't help so you really have to ask lots of questions of the seller to make sure you get what you want.

I would say that most AF models were originally fire engines. These tend to make great doner vehicles because they quite often have the desirable fast axles and above all they are usually in great condition having spent their whole life indoors being polished.

I will let someone more technical explain the ratios

Neil

 

[Joe917]

With regard to the 2 or 4wd

If the model number has an A in it such as 1017A or 917 AF , this states that vehicle has 4wd.

what it doesn't tell us is if the 4wd is permanent or switchable from 2wd to 4wd.

it would appear that there is no hard or fast rule. Mercedes made several variations in each model.

for example my 1017 came in switchable 2wd to 4wd. It also came with either a rear difflock or both front and rear difflock.

So unfortunately its really hard to confidently identify what the vehicle has simply by the model number.

Its also means there is no so easy to tell even if you see the vehicle. For example the pneumatic dial shown a couple of pages back on a permanent 4wd model might simple select a high range and a low range and a neutral. Whereas on my vehicle, the exact same dial not only selects high and low range but at the same time selects 2 or 4wd

I know this doesn't help so you really have to ask lots of questions of the seller to make sure you get what you want.

I would say that most AF models were originally fire engines. These tend to make great doner vehicles because they quite often have the desirable fast axles and above all they are usually in great condition having spent their whole life indoors being polished.

I will let someone more technical explain the ratios

Neil

Thanks Niel, so does your truck have locking hubs? Seems strange to switch to 2wd but still turn the entire drivetrain. (sorry to the OP for the thread drift!)

 

[mog]

When buying my 1017 i looked at maybe a couple of hundred in various German military auctions via VEBEG .
All were the same. 2 or 4wd with rear diff lock.

Is there a simple test (other than jacking the front and back of the vehicle and operating) to tell if 'with locker(s)' the truck operates like the Operator's Manual states, or if it operates in true 2x4 mode? That would certainly be a good to know test if checking in person, or talking with a dealer/salesperson. I think many salespeople just assume the 2x4 mode.

The first letter following the numbers A-all-wheel drive, Second letter (if there) B-concrete mixer, F-firetruck, K-dump truck, KO-municipal, S-tractor truck. For engines, A- turbo, AL - turbo & intercooler. Again, from the Mercedes manual, so real world may vary.

 

[Neil]

Thanks Niel, so does your truck have locking hubs? Seems strange to switch to 2wd but still turn the entire drivetrain. (sorry to the OP for the thread drift!)

No it doesnt as standard, although the can be fitted.

Yes i have always thoughg it a bit odd. Obviously its spinning the diff and the forward prop shaft but it has no resistance from the transfer box until 4wd is engaged.

This system is common on many oldtime mercedes such as 1113a and 911a

I quite like it. For 99% of travellng 2wd works fine

Neil

 

[mog]

OK, questions.. I am really confused, some overspill in this thread from my build thread too..

• How do i know if i have fast or slow axles? (FRONT AXLE, RATIO 39:8, REAR AXLE, RATIO 43:10)?
• The discussion over permanent 4x4 or 4x2 (4x4 then engaged with the low range transfer case) is still very unclear, can someone please shed some light on this?

If you (or someone else) enters your VIN in the Mercedes Electric Maintenance and Parts catalog, it should show which axles your truck is equipped with.
I only have 2 examples my 1017AF without lockers, operates as the Operator's Manual describes, 2x4 in road mode, 4x4 in offroad mode, and my friend's 1017A with a rear locker, 4x4 (unlocked) in road mode, and 4x4 (locked) in off-road mode. But it sounds like there are 'hundreds' of trucks that are different than described in the manual. It would be a lot of hassle, but running the truck on jacks, you could tell, or (hopefully a better plan/test). I don't know of any 'factory' locking hubs. Mine were aftermarket from AVM

 

[palebluewanders]

OK, questions.. I am really confused, some overspill in this thread from my build thread too..

• How do i know if i have fast or slow axles? (FRONT AXLE, RATIO 39:8, REAR AXLE, RATIO 43:10)?
• The discussion over permanent 4x4 or 4x2 (4x4 then engaged with the low range transfer case) is still very unclear, can someone please shed some light on this?

From what I have seen (and someone correct me if I'm wrong), these MBs come in 3 axle ratios:
Slow 5.25 (42: 8)
Medium 4.8 (39: 8)
Fast 4.3 (43:10)

So it looks like you have a mix of medium and fast? If you're thinking about converting the front axle to fast as well, there are threads about that in the ln2 forum which I saw you also joined. Let me know if you want me to find you the links.

As for the rest of this discussion about diff locks and free wheeling hubs etc. it sounds important and was on my list of things to learn about this weekend anyway so hopefully then I'll understand what's going on! ?

 

[palebluewanders]

Okay, I have educated myself a bit but still want to ask: is there a practical or fuel consumption difference between: 1) part-time 4wd where you switch between 2wd and 4wd via transfer case and 2) permanent 4wd where you lock/unlock the center diff? As I understand it in case 1 it drives one out of two wheels in 2wd mode and in case 2 it drives one out of four wheels while center diff is unlocked (right?) but in what ways does that actually matter?

On a different note, @mog very telling that even a M.A.N. engineer would choose an MB 1120 in some cases! Can't go wrong with this truck it seems. :⁠)

 

[Sitec]

Hey @Sitec! We are aiming for a 3.6m wheelbase since our current layout plans have 4.5m interior length. Ideally LHD but we plan to go to a lot of both LHD and RHD countries so RHD wouldn't be a deal breaker.

1820! Never considered anything rated that high, I always kind of assumed the suspension would be way too stiff for our ~8t load?

3.6 should work well with a 4.5m hab box. Hot tip though... If your house has a room that's big enough, mark out a 4.4m x 2.4m rectangle (allowing for 50mm wall thickness, and then move mattress's, seating, cooker, fridge etc into it and see how it feels for size... When you see the box taped up on the floor, it makes for interesting discussions/planning...

Re that 1820, ours is a 1222a which is basically identical in looks to that 1820 (except the engine), and ours is plated at 13300kg. With our hab box on, the rear chassis leaf stops don't reach the rear helper springs... Once the truck is on the road and furnished that might change, but if not I'll prob remove the spring that are not required. You can match the springs to the load by removing leaves. Ours needs the whole front pack, but looks like it could loose the rear helpers. Don't forget 8 tonnes of load plus 5 or 6 tonnes of truck... plus a tonne of water and diesel adds up... I'd like our whole finished build to be under 10 tonnes, but I'm tipping it'll be nearer 12!

 

[Madoxen]

We chose an 1835 for our build and so far im pretty happy, that extra power means it just does not care if its on a hill or the flat it will sit at the speed we put it. Mind you we are in the build process so will have to let u know what its like when finished. even though its an 1835 because its only 2 axle it is actually only allowd 14 ton not the 18 in nz.

 

[Sitec]

OK, questions.. I am really confused, some overspill in this thread from my build thread too..

• How do i know if i have fast or slow axles? (FRONT AXLE, RATIO 39:8, REAR AXLE, RATIO 43:10)?
• The discussion over permanent 4x4 or 4x2 (4x4 then engaged with the low range transfer case) is still very unclear, can someone please shed some light on this?

Very slow axles = 80kmh flat out... Slow axles = 95kmh flat out... Fast axles = 110kmh and beyond! (this is roughly and depends on tyre sizes...) The ratios can be different in some trucks, as some trucks have hub reduction axles... In this setup, the front axle does all its reduction in the diff itself, as the shafts then connect directly with the wheels. The rear hub reduction axle can have a smaller/slimmer diff with a closer ratio, as there can then be further reduction in the hubs (the huge lump in the rear wheel centers), as these contain epicyclic gear sets.

Permanent 4x4 = All 4 road wheels are driven all the time, and the vehicle will have a lockable central diff (between the front prop and rear prop situated in the transfer case). There may be optioned axle diff locks in the front and rear axles. A central lockable differential has to be in the system, because the front axle of a permanent 4x4 vehicle has to have the ability to travel a greater distance (picture a truck going around a roundabout from above) as the front wheels travel a further distance/greater arc when turning. The center diff lock then gives the driver the option to lock the front axle and rear axles together, so when off road both axles are driven 50/50.

Selectable 4x4 = The vehicle drives on the rear axle only (front axle is pushed along and all shafts are still turning, but the axle is not driving/live). 4x4 is then selected by a separate switch, or by selecting low range (this varies dependant on vehicle and model). There still also may be optioned axle diff locks in the front and rear axles.

There are advantages and disadvantages over both systems... With selectable 4x4 you can option the front axle with free wheeling hubs (which physically disconnects the front wheels from the axle itself), which in turn saves fuel as the front axle components, front prop shaft etc are not having to be pushed along.

With full time 4x4, the vehicle has a different feel to it. The front axle pulls the vehicle into corners, giving it a more positive driving feel. I personally think it comes into it's own on dirt roads. Both axles also share the load (which is great on trucks with thumping great engines). The downside is that full time 4x4 uses more fuel.

My choice... Full time 4x4 as I grew up with Defender Land Rovers (the real ones), but in reality, selectable 4x4 is probably better as you can save quite a bit of fuel, and we don't all drive on gravel roads and flat out! Hope this helps explain it.