Frame Stretch
- Thread starter dzzz
- Start date
dzzz
™
So, here's my take after research.
I can see a u500 stretch costing $15K if using Mercedes parts to maintain the warranty. Especially if these parts are shipped air freight.
But I'm not going to do the Mercedes parts on a truck out of warranty. I'm going to have the fabricator have the parts made in his usual way. Either way going from 3900 to 4800mm wheelbase requires an intermediate bearing.
Mercedes-Benz Special Trucks (Germany) was extremely prompt and helpful with advice. In this instance I'm not taking their advise, but I'm still impressed. For the record here is their recommendation:
A wheelbase extension of 900mm (3900mm to 4800mm) can be realized but I would not recommend it rather you need it necessarily.
The longer the wheelbase of the Unimog gets, the larger is getting the
negative impact on the excellent offroad-capabilities. For example the ramp
angle (when driving over a crest after an incline) is getting significantly
smaller and the turning circle is getting larger.
The turning circle of a Unimog with 3900mm wheelbase varies between 16.8m
and 17.6m depending on the tires. The turning circle of a Unimog with
4800mm wheelbase will be approx. 21.6m (4600mm wb: 20.7m).
Another point is the drive shaft of the rear axle. With a wheelbase
extension of 900mm to 4800mm, you will need a drive shaft with an
intermediate bearing, which results in a higher chassis empty weight as
well as a more expensive modification. In case of a 4600mm wheelbase, you
can use a MB-drive shaft without an intermediate bearing.
Also an important point is the payload distribution between front axle and
rear axle. The rear axle of a vehicle with a long wheelbase can easily be
overloaded. So when designing the body (e.g. RV, flat bed etc.) a detailed
axle load calculation need to be done to avoid overloading the rear axle
and under-running of the minimum front axle load of 33% of the actual
vehicle total weight (e.g. Total weight: 20,000lbs; Min. front axle load:
20,000lbs x 0.33 = 6,600lbs).
Please let me know, which kind of application you thinking about to realize
with the Unimog with extended wheelbase. In case you already have done an
axle load calculation, I would appreciate to take a look at it. I attached
an axle load calculation form to this email.
Further on, I would like to know, if a wheelbase of 4600mm fits your needs.
You should have the Unimog Body & Implement Mounting Guidelines on hand for
designing a body for the Unimog and doing a wheelbase modification. The
guidelines contain important information, which must be considered.
I can see a u500 stretch costing $15K if using Mercedes parts to maintain the warranty. Especially if these parts are shipped air freight.
But I'm not going to do the Mercedes parts on a truck out of warranty. I'm going to have the fabricator have the parts made in his usual way. Either way going from 3900 to 4800mm wheelbase requires an intermediate bearing.
Mercedes-Benz Special Trucks (Germany) was extremely prompt and helpful with advice. In this instance I'm not taking their advise, but I'm still impressed. For the record here is their recommendation:
A wheelbase extension of 900mm (3900mm to 4800mm) can be realized but I would not recommend it rather you need it necessarily.
The longer the wheelbase of the Unimog gets, the larger is getting the
negative impact on the excellent offroad-capabilities. For example the ramp
angle (when driving over a crest after an incline) is getting significantly
smaller and the turning circle is getting larger.
The turning circle of a Unimog with 3900mm wheelbase varies between 16.8m
and 17.6m depending on the tires. The turning circle of a Unimog with
4800mm wheelbase will be approx. 21.6m (4600mm wb: 20.7m).
Another point is the drive shaft of the rear axle. With a wheelbase
extension of 900mm to 4800mm, you will need a drive shaft with an
intermediate bearing, which results in a higher chassis empty weight as
well as a more expensive modification. In case of a 4600mm wheelbase, you
can use a MB-drive shaft without an intermediate bearing.
Also an important point is the payload distribution between front axle and
rear axle. The rear axle of a vehicle with a long wheelbase can easily be
overloaded. So when designing the body (e.g. RV, flat bed etc.) a detailed
axle load calculation need to be done to avoid overloading the rear axle
and under-running of the minimum front axle load of 33% of the actual
vehicle total weight (e.g. Total weight: 20,000lbs; Min. front axle load:
20,000lbs x 0.33 = 6,600lbs).
Please let me know, which kind of application you thinking about to realize
with the Unimog with extended wheelbase. In case you already have done an
axle load calculation, I would appreciate to take a look at it. I attached
an axle load calculation form to this email.
Further on, I would like to know, if a wheelbase of 4600mm fits your needs.
You should have the Unimog Body & Implement Mounting Guidelines on hand for
designing a body for the Unimog and doing a wheelbase modification. The
guidelines contain important information, which must be considered.
charlieaarons
Explorer
Acutally, lengthening the wheelbase by 700mm but only putting a 400mm longer camper on would transfer a bit of weight to the front. Except it would also allow a square cut rear compartment, instead of tapered. Which would allow a packrat like me to put more heavy junk in it.
Charlie
Charlie
dan johnson
New member
Doing a frame stretch on a straight framed truck if fairly common. I had a 18-wheeler that I used to haul my unimogs around the country with. Getting tired of having to stop at weight stations and filling out log books I decided to have it made into a camper. I checked around and there were many places that would stretch a frame. I had one estimate for $1800. You can see the process at http://www.dansunimogs.com/ under the unimog hauler. Would have make a great expedition vehicle except for the 4 inches of ground clearance and 2 wheel drive. Looking under my U500 it looks like a frame stretch behind the transmission just before the supports for the rear axle would be the logical choice. You would only have cut and add to the frame, the drive shaft, the support arm that goes from the rear of the transmission to the rear axle support, air line for the brake and some wiring for the rear lights. Any good truck frame shop should be able to do the frame. I have had numerous drive shafts lengthened and shortened at a good drive shaft shop. Sounds like if you keep it under 700mm you do not need a carrier bearing but if you decide to go over that you should use one. Carrier bearings are an off the shelf item most 18 wheelers have them and all school buses. The transmission support looks to be about a 1 inch piece of steel tube and you could up size that a bit and just make a new one. The air line and electrical wires should be no problem.
Dzzz I think you should go for it. Keep us posted on how it goes.
Dan
Dzzz I think you should go for it. Keep us posted on how it goes.
Dan
dan johnson
New member
Any pictures of the stretch. Where did you cut the frame.
Dan
Dan
dzzz
™
The frame is cut roughly half way between the cab and the rear axle. The steel is not typical (for the U.S.) frame material, so it's probably best to not let the shop use whatever material they usually use. Unimog U.S. and Germany are very helpful and have specs on how it should be done.
A large number of cab chassis are stretched or shortened. What I learned is that this is a specialized business. What needed with the U500 is finding a vendor that will do the research to do it right. My guy is also putting in two 100 gallon fuel tanks. Except for the tank itself he's using all Unimog parts.
A big reason I stretched the fame was to have the room in front of the rear axle for 200 gallons of fuel.
It surprised me that my vendor wanted to use all unimog parts. But I'm glad he researched it enough to reach that decision.
I'm only referencing the U500 straight frame. I don't know if the other mog frames can be modified.
A large number of cab chassis are stretched or shortened. What I learned is that this is a specialized business. What needed with the U500 is finding a vendor that will do the research to do it right. My guy is also putting in two 100 gallon fuel tanks. Except for the tank itself he's using all Unimog parts.
A big reason I stretched the fame was to have the room in front of the rear axle for 200 gallons of fuel.
It surprised me that my vendor wanted to use all unimog parts. But I'm glad he researched it enough to reach that decision.
I'm only referencing the U500 straight frame. I don't know if the other mog frames can be modified.
charlieaarons
Explorer
There will be some extra room on the right side in fornt of the rear axle.
What are you going to put there?
Charlie
What are you going to put there?
Charlie
dzzz
™
Storage box
132" frame stretch
I came across an 2002 132" wheelbase fully loaded, but I`m also interested in stretching the frame.
Does anyone know if it would be feasible to stretch this size frame?
I`ve been looking for the 154" and come across one, but it`s been well used, i.e., somewhat abused. I would rather find one in the best condition possible.
I came across an 2002 132" wheelbase fully loaded, but I`m also interested in stretching the frame.
Does anyone know if it would be feasible to stretch this size frame?
I`ve been looking for the 154" and come across one, but it`s been well used, i.e., somewhat abused. I would rather find one in the best condition possible.
dzzz
™
I'm sure it's feasible, but I don't know the differences between the short and long wheelbase.
Iain_U1250
Explorer
Charlie is probably somewhere in either Western Australia or the Northern Territory - with luck he will be back in range in a week or two,
I'm not sure either. Where's Charlie when you need him?