Frame Stretch

[dzzz]

Or where to place the rear axle.

The long U500 has the wheel base of a typical american pickup. Pretty short for a 16' box. As suggested in another thread adding 900mm (3ft for my fellow Imperialists) may be a good choice - 3900mm + 900mm. That puts the length at a standard size which seems particularly appropriate for a well organized German truck owned by a american of German decent.

But what is optimal rear axle placement for a given body length? I don't believe break over angle is as important as actual body clearance. But certainly it's possible to place the axles too far apart. If I don't care about keeping to a standard wheelbase, how do I place the rear axle?

 

[charlieaarons]

why don't you click on the different body lengths for the Terracross line of Unicats for suggest wheelbase to body length relations? The pictures of hypothetical vehicles are at the bottom of each page you link to:
http://www.unicat.net/en/index2-TerraCross.html
For example for a 4900mm camper and a 3900mm or 4200 wheelbase, a tapered rear body is recommended. For a 4500mm wb, a squared rear body is OK, allowing a LOT more storage space in the rear compartment (wish I had that!)
On the 5200mm camper click-link, he recommends a 4500mm wheelbase and a tapered body. A 4800mm wheelbase would allow a squared rear edge. That size camper in comparison with mine would offer larger water tanks and perhaps more batteries, or else a larger bathroom and over/under fridge/freezer, but not both.
I'd think with a 4800mm wheelbase a 5500mm body would be feasible. Allowing, in comparison with mine, an extra storage closet on the left or alternatively 600L of water capacity (I have 440L), and on the right a larger fridge over a freezer. and perhaps even more batteries (1260Ah instead of 840!)
Also, below the camper, the extra 36" would allow a 95 gal fuel tank even with the generator instead of my shortened 40 gal tank, and on the driver's side a ~60-70 gal "squared" Euro type aux tank. I'd make my rear behind axle tanks shorter for better ground clearance to ~50 gal instead of 61 gal for total tankage of ~260 instead of 162 gal. One could do the Canning Stock Route (1100 mi., hundreds of dune crossings) without worrying about extra fuel or even jerrycans.
But I probably wouldn't make the U-turn at Northern Lights and Lake Otis to get to work...

Charlie

 

[Allroader]

Hello Dzzz,

As you know we strechted our Truck.
We went with a 900mm extra, to fit our Box on. Which will is 4,60m (about 15') and the spare tire will be standing on the frame behind the box.
This leangth was original made by Mercedes, so the new driveline was a new original MB Part. We could have choosen any length and had a custom driveline made. Would have not cost any more. But being able to use a original MB Part, is a nice thing. Who knows if and where the thing might break someday.

Mike

 

[dzzz]

What I'm leaning towards is a 5200mm squared camper on a 4800mm wheelbase. Unicat only shows 4500mm wheel base on the U500. Perhaps they can get 4500mm from the factory.
I believe a 900mm stretch to 4800mm leaves enough departure angle without slanting the camper in the back. But I'm not certain.
This change allows me to keep the original fuel tank, as well as put a large black tank in the camper just aft of the rear axle.
As Charlie pointed out in another post the benefits of the stretch are significant, given the short nature of the longest U500.

 

[charlieaarons]

A squared off 5.2m camper will be fine on a 4.8m wheelbase.

Charlie

 

[alaskaboy]

Where would one find a composite list of shops that can perform Mercedes approved frame lengthening? Seems like experience would be highly desirable given differing design expectations of the Mog frame and potential catastrophic consequences of failure.

 

[charlieaarons]

You'd have to call Unimog NA and ask David Looney or Traian Grecu.
Do you really want to do it?
Do you live in Alaska with a U500?

Charlie

 

[dzzz]

Where would one find a composite list of shops that can perform Mercedes approved frame lengthening? Seems like experience would be highly desirable given differing design expectations of the Mog frame and potential catastrophic consequences of failure.

Be aware that the U3/4/500 are straight ladder frame with a driveshaft. Other types of mogs are more exotic.

I've only ever heard of a stretch on a U500.

Heavy duty trucks with a straight frame are good candidates for a stretch on a camper build. Personally I wouldn't consider it on a light truck like the small Fuso or an exotic like most mogs.

 

[alaskaboy]

You'd have to call Unimog NA and ask David Looney or Traian Grecu.
Do you really want to do it?
Do you live in Alaska with a U500?

Charlie

Do I really want to? Yes.

Do I Have U500? Unfortunately no.

I am really looking hard for an overlander for the whole family 2 adults and 3 kids, mostly domestic, but potentially foreign travel. I idealy envision a 22 to 25' maximum foot vehicle with a pop top on a stretched U500. There is a beauty of a used cabin on unicats second hand site but it is just too long (did I say expensive as well). I couldn't get a specific weight on the cabin, but they said it excluded the U500. I am keeping my eye out for a pre-emissons class 7/8 as weight would be less of an issue at the cost of length and preference for a coe. I plan to contact Avi with unicat to see if a scaled down version is possible. I know all things are possible at the right price.

I have spoken with GXV and plan to meet with them at the expo in April. They intimated they might be showing a different kind of vehicle (?).

Self build would be fun as well, but who has the time. Appreciate all your input on the forum.

mnb

 

[dzzz]

It's going to be tough to do a U500 with five people. There may be a doka extension in the U.S. that's unused. But integrating the doka into the camper is not easy. I did briefly look at adding a doka when one was available at a good price last year.

IMO the ideal medium size design for families would be one in which cab seating and camper seating are the same. Maybe a long Sprinter.

 

[alaskaboy]

It's going to be tough to do a U500 with five people. There may be a doka extension in the U.S. that's unused. But integrating the doka into the camper is not easy. I did briefly look at adding a doka when one was available at a good price last year.

IMO the ideal medium size design for families would be one in which cab seating and camper seating are the same. Maybe a long Sprinter.

I think you would just run out of wheelbase too quickly to have a Doka. The cabin dining area would have to do double duty as passenger seating which is a compromise worth considering to get the other benefits of the U500. An extended cab truck would be nice, but its not just the extra 3 feet of cab space, its the additional 3-5 feet of hood that comes with a conventional truck. Total cost of 6 to 8 feet!

The sprinter is just not up to extended stays where it is often wet and cold in our neck of the woods and everyone is inside reading and the like.

I'm open to any ideas or base vehicles. I suspect a class 6 truck is our minimum at 19k -26K GVW.

 

[charlieaarons]

.

I'm open to any ideas or base vehicles. I suspect a class 6 truck is our minimum at 19k -26K GVW.

A Western Star 4900SA 6X6 with DD15 engine and Roadranger 9ALL 11 spd with ultra low creeper gears; autoshifting version (like the U500) available.

Charlie

 

[Iain_U1250]

My build on a U1250 has a two seater bench seat in the camper section - whilst the two rear passengers can see through the large crawl through, it is a bit restricted due to the sideways set-up. I could fit and additional seat opposite the bench seat, but don't really have the need.

Having the two rear seats meant that according to our "Australian Design Rules" I have to have "approved seat and seat belt anchorages, and a " substantial structure" on the rear cab - I have a fully braced steel frame that acts as a roll cage strong enough that the certifying engineer considers it to to be "substantial".

Sleeping space for the two passengers will be a roof top tent over the cab or a tent pitched next to the truck- probably not so good where it is cold - but then people sleep in tents in the Arctic. My wife an I prefer our privacy and I think our kids or guest would feel the same - I could not stand having to bunk with other people in the truck - certainly not conducive to "good marital relations" anyway .

 

[michaelvanpelt]

Unimog Doka?

It is possible to still do a DOKA on a U500 however it is expensive. The frame strech to the recomended length is 181" and can be done by Fontaine or Tulsa Truck... Fontaine did our 181" wheelbase. It added approx $15,000 plus shipping and without the DOKA change allowed for a 16 to 17 foot body. The DOKA would add approx $45,000 to $55,000 possibly more and the expedition body would have to be smaller.

Western Star does not make a extended or crew cab however it can be done aftermarket. But again expensive.

Freightliner and International can do an extended or crew cab in a 4x4 or 6x6 version. Locking diffs can be added or ordered. In my humble opinion this is the better option as the 260 HP Unimog would get a bit slow with all the added weight of a DOKA and longer expedition body.

 

[Trausti]

frame stretch

Here are some useful information about frame stretch by MB Unimog.
https://bb-infoportal.mercedes-benz.com/portal/ar_unimog.0.html?&L=1

Best reg.
Trausti
Iceland