MB 917 vs 1120/1124?

[Geo.Lander]

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.

Thanks Sitec for taking the time to explain this! regarding slower or fast axles, is there a way know what i have from my axle ratios I posted?
I have a center and rear locking diff but I am still no closer to figuring out if 4x4 is only engaged when either using the center diff lock (that should go without saying) and/or as some have been saying while engaging the low range box..

 

[palebluewanders]

@Sitec Great tip about doing a live simulation of our layout! I'm currently living in a campervan but maybe during our next house sit we'll try this exercise (maybe without moving the homeowner's furniture and appliances around though ?).

Sorry I meant mine would be 8t including the truck, water, and diesel! I believe the 1120s/1124s are probably around 5t (maybe?), so the habitat should only be 2.5 - 3 tons I think. All of that is pure conjecture at this point though; we haven't even figured out what kind of habitat it's going to be. At first I was leaning toward a custom build but saw in @Geo.Lander's thread the crazy lead times and/or prices so now I'm considering a refrigerated truck body but they're not that easy to find! So who knows on this.

Good luck trying to shave some weight off of yours, if you're really aiming for the 10t mark!

 

[palebluewanders]

@Maxoden Amazing build thread! It's so great that you and so many others here have gone into such detail with the process. There are so many things I'd have no idea I'd need to do/consider otherwise. And that 1835 sure looks huge, bet she'll be a real luxury when she's finished (and definitely more pretty than ugly)!

 

[Geo.Lander]

@Sitec Great tip about doing a live simulation of our layout! I'm currently living in a campervan but maybe during our next house sit we'll try this exercise (maybe without moving the homeowner's furniture and appliances around though ?).

Sorry I meant mine would be 8t including the truck, water, and diesel! I believe the 1120s/1124s are probably around 5t (maybe?), so the habitat should only be 2.5 - 3 tons I think. All of that is pure conjecture at this point though; we haven't even figured out what kind of habitat it's going to be. At first I was leaning toward a custom build but saw in @Geo.Lander's thread the crazy lead times and/or prices so now I'm considering a refrigerated truck body but they're not that easy to find! So who knows on this.

Good luck trying to shave some weight off of yours, if you're really aiming for the 10t mark!

I think the raw base truck of the 1120 are just over 4100 kgs depending on your cab configuration/options (this is based on youtube). I was told a normal 5m 6 point subframe was about 6-800kgs. So at this point a lighter GRP kit or ex-military aluminium body might be your choices the later being quite a bit heavier but much stronger.. We just moved house and are making some connections in the local community and there are significant resources for box building (SKAB Norge AS) and other truck facilities within walking distance. We are aiming at under 7500kg, the rest of the calculation comes down to fuel, water, interior construction and what toys you are bringing along ??.

We have sort of decided on a few design principles already:

• Internal framing mixed with 2020 aluminium extrusion system and poplar plywood (which we will later veneer using the 3M PSA system)
• Lighter fuel (300l), battery (200-300Ah) and water capacity (220L) but with space to add another water tank
• We are going for a 4.9m long ex-danish military radio box, we will try and strip out as much weight as possible and have the subframe and painting done in Germany (that is the plan for now anyway

 

[palebluewanders]

Hmm, I saw (also on YouTube) that the 917 is 4.25t so I just arbitrarily rounded up to 5 in my head for the 1120/1124 haha. If they are basically the same as the 917 that's good news for me!

Those truck facilities sound like perfect connections! What a great resource.

What is the radio box made of? Is it insulated already?

 

[Geo.Lander]

Hmm, I saw (also on YouTube) that the 917 is 4.25t so I just arbitrarily rounded up to 5 in my head for the 1120/1124 haha. If they are basically the same as the 917 that's good news for me!

Those truck facilities sound like perfect connections! What a great resource.

What is the radio box made of? Is it insulated already?

Yes, they are supposedly very well insulated, full aluminium construction. They are designed to be shipped as containers for logistical purposes, so they are very strong indeed. I see a lot of people using these boxes on their builds including some "famous" trucks like the one Ulrich Dolde has. But there is very little info I have found regarding sourcing and building them out (what to expect, how well insulated are they, etc, etc).. So I am little in the dark too..

 

[Geo.Lander]

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! ?

Thanks! I totally missed this post! I knew the ratios just didn't know how to read them!

Right, im not sure why I have a mix of axles but I am sure someone here can explain that, if it is not normal etc. I am also adding the bigger 385/65/22.5 wheels in the spring time so ill have to see how much of a difference that makes to highway speeds (on most main roads we will be traveling on the limit is 80km/h anyway).

Yes, if you could post the link that would be great! I was not planning and changing to fast axles but good anyway!

I am thinking that the reason there is a mix of axle ratios now might be because of the 4x2/4x4 we have been discussing. Maybe my truck is 4x2 when the center diff lock is not engaged? that would explain quite a bit...?

 

[palebluewanders]

Yes, they are supposedly very well insulated, full aluminium construction. They are designed to be shipped as containers for logistical purposes, so they are very strong indeed. I see a lot of people using these boxes on their builds including some "famous" trucks like the one Ulrich Dolde has. But there is very little info I have found regarding sourcing and building them out (what to expect, how well insulated are they, etc, etc).. So I am little in the dark too..

Oh! I have that book too and knew Ulrich went for a Zeppelin shelter but didn't realize that was the same thing as a radio box, heh. Seems like a good choice.

 

[palebluewanders]

Thanks! I totally missed this post! I knew the ratios just didn't know how to read them!

Right, im not sure why I have a mix of axles but I am sure someone here can explain that, if it is not normal etc. I am also adding the bigger 385/65/22.5 wheels in the spring time so ill have to see how much of a difference that makes to highway speeds (on most main roads we will be traveling on the limit is 80km/h anyway).

Yes, if you could post the link that would be great! I was not planning and changing to fast axles but good anyway!

I am thinking that the reason there is a mix of axle ratios now might be because of the 4x2/4x4 we have been discussing. Maybe my truck is 4x2 when the center diff lock is not engaged? that would explain quite a bit...?

Sure thing, here is the report about changing the front axle ratio.

@Sitec's explanation above about hub reduction axles sounds like it's related to your different axle ratios but more research is needed on my end to figure out what that really means, heh.

 

[Geo.Lander]

Sure thing, here is the report about changing the front axle ratio.

@Sitec's explanation above about hub reduction axles sounds like it's related to your different axle ratios but more research is needed on my end to figure out what that really means, heh.

Thanks for those links, the PDF report is very detailed indeed… I am not planning such a task at present until I get to know my vehicle a bit more.

Regarding my mixed ratio axles, i have some musings... I think it's the central differential that compensates for the ratio difference with primary/most power being sent to the rear axles unless the centre diff lock is engaged. Still permanent 4*4 but the difference in axle ratio is actually what determines the rear power bias.. this would make sense to me at least

I'm just making assumptions here, so please correct me, I also don't think (1120) the transfer case engagement enables 4*4 as some have stated about their particular trucks..

 

[VerMonsterRV]

I "think" our 1120 is full time 4wd with all open diffs. We have lockers rear and center. I think low range is just low range. While the front wheels are jack off the ground, if you spin them the front drive shaft spins.

Our 1120, fitted out with a rail on subframe, composite habitat and motorcycle lift etc, we weigh in at just around 20,000lbs fully loaded. Now without the motorcycle/lift we could likely shave off 1,000lbs, so getting lighter will mean just less equipment or smaller habitat.

 

[Neil]

. While the front wheels are jack off the ground, if you spin them the front drive shaft spins.

Mine does this in 2wd mode. Its tge easiest way to get tgevright angle on the prop shaft joints to line up the acces to the grease nipples.

You only need to raise one wheel of the ground to spin the prop shaft. Same for the rear one.

Not sure this is conclusive proof that its permenant 4wd

I think if you were to raise both front wheels and put it gear ( engine off ) then try and spin the wheels and se if they spin freely might be more of an indication.

Neil

 

[Joe917]

Mine does this in 2wd mode. Its tge easiest way to get tgevright angle on the prop shaft joints to line up the acces to the grease nipples.

You only need to raise one wheel of the ground to spin the prop shaft. Same for the rear one.

Not sure this is conclusive proof that its permenant 4wd

I think if you were to raise both front wheels and put it gear ( engine off ) then try and spin the wheels and se if they spin freely might be more of an indication.

Neil

I find driving forwards a foot turns the prop shaft to the right spot, it never seems to be right for all 9 grease points! Easier than jacking a wheel.
Neither one of those tests indicate permanent 4wd. Repeat it next time with the transfer case in high in gear and then in neutral, repeat in the low position. A free wheeling front wheelin transfer case high and transmission in gear would be an indication of 2wd. You should not be able to turn just a single wheel in 4wd unless you are in neutral.
I'm sure I have seen somewhere bump starting the engine by spinning a jacked up wheel in neutral then putting it in gear, I think it was a Land Rover.

 

[Kurben]

Thanks for those links, the PDF report is very detailed indeed… I am not planning such a task at present until I get to know my vehicle a bit more.

Regarding my mixed ratio axles, i have some musings... I think it's the central differential that compensates for the ratio difference with primary/most power being sent to the rear axles unless the centre diff lock is engaged. Still permanent 4*4 but the difference in axle ratio is actually what determines the rear power bias.. this would make sense to me at least

I'm just making assumptions here, so please correct me, I also don't think (1120) the transfer case engagement enables 4*4 as some have stated about their particular trucks..

Front and rear axle ratios are always the same. What is printed on the labels on front and rear axles? What does the Mercedes Benz parts catalog show when you check your VIN? What are the SA codes starting with A..?

 

[charlieaarons]

Front and rear axle ratios are always the same.

Actually not completely true. There’s many examples of 4wd vehicles with front diff slightly faster (~1%) than rear e.g. front 4.27, rear 4.30. This actually can have a stabilizing effect on surfaces like ice. Conversely the opposite (rear faster than front) can contribute to tendency to switch ends on ice.