Unimog as a cross country RV.

Would a fast axle Unimog make a good cross country expedition RV?

thanks, J

"Fast Axle" is a misnomer that I wish would DIE! Yes it actually is a MBZ designation for a slightly higher ring and pinion. Super Fast Axles would be ring and pinion AND hub gears.

However, the devil is in the details. MB went to Fast Axles as standard equipment on the OM366A engines. The OM366A turbo charged engine are governed at about 2600 RPM. The older OM352 naturally aspirated engines are governed at about 2900 RPM. The difference in the Fast Axle gear Ratio is about the exact same difference of 300 RPM!

Therefore..........A naturally aspirated Unimog U1300 with standard axles has almost the same exact top speed as a turbocharged U1300 with fast axles.

More related to your question. With enough money and modifications, the Unimog can make a good highway cruiser if you are willing to accept 60 MPH as a good cruise speed. If you have visions of 75 MPH for extended periods, while theoretically attainable, you will be having hub reduction failures. Bottom line with few exceptions, the Unmogs were never designed to cruise at what we consider normal freeway speeds.

We have some good friends from the Netherlands. Built there Unimog camper and came to the United States. Showed up at my shop about 6 months in and asked if I would sell there truck as they were going home to build a new truck. We sold it, they went home and 14 months later arrived with a MAN truck with straight axles. There reasoning was straight forward....a vast majority of North America, the Unimog is overkill. They proceeded to spend the next 5-6 years running North and South America and taking their MAN thru places that would make most people cringe. His list of refined reasons...Better Mileage, less complex, 70 MPH cruise speed, and more reliable. Only an opinion, but some food for thought.

Cheers,

Scott

Thanks Scott, exactly what I wanted.

Joe

I have an 87 U1300L with the fast axle ratios the truck is well within all limits driving at 55 mph, the one issue you would have in driving one of these trucks for thousands of miles at road speeds is in the portal drives to each wheel, they are not terribly fond of continuous high speed hi-way driving, your going to have some excessive heat build up and there is going to be some premature wear in the portals. Is this a serious problem? I have a friend who runs a Unimog 1300 that used to be a firetruck and he has the Claas overdrive unit in his truck and he can drive the truck at 60 to 65 mph and he has never had a problem, and he has taken some pretty long trips with his truck, maybe he will chime in on this thread, his user name is Tennmogger, he is one the most knowledgeable Unimog folks I have ever met, and he has helped me out on numerous occasions. The other possible issue you would run into with a Mog is IF you ever did have a problem on the road in the US you are going to be waiting for parts!, the parts are in this country but they need to get to your location. As far as the truck goes, in my eyes there is NO BETTER truck than a Unimog bar none!
Good luck, and if you look into a MAN truck your going to be waiting for parts also!
Karl

Reviving an old thread as I am looking at rigs now:
MAN G90
Unimog U1300L NA with fast axles
FMTV M1083

All very different rigs, yes.
The FMTV, in the US, makes sense, as any big rig shop can help out, but it's HEAVY.
The other 3, I understand parts could be harder to find, longer to receive.
The MAN doesn't have portals but I don't know much about them.

A lot of real world info here.

When you add a large habitat that is heavy and raises CG, wide as or wider than the Unimog, maybe decreases departure angle, you just limited where the vehicle can go. The abilities of the vehicle, and the benefits of a Unimog have been negated.

Then consider the desire to push the Mog beyond it's designed speed parameter, the inability to have it towed (can't pull an axle or drop a driveshaft), no shops to do repairs, and somewhat of a parts procurement issue. Then the hub issue.

After putting over 100k km on our U1300, Om-366A turbo with faster axles (ex-fire truck) and overdrive, we moved our Alaskan camper to an LMTV and eliminated the breakdown concern.

But I miss the 14 mpg of the mog compared to 6 for the LMTV.

Best solution: get a Unimog, a lightweight shelter, and slow down.

tennmogger said:

When you add a large habitat that is heavy and raises CG, wide as or wider than the Unimog, maybe decreases departure angle, you just limited where the vehicle can go. The abilities of the vehicle, and the benefits of a Unimog have been negated.

Then consider the desire to push the Mog beyond it's designed speed parameter, the inability to have it towed (can't pull an axle or drop a driveshaft), no shops to do repairs, and somewhat of a parts procurement issue. Then the hub issue.

After putting over 100k km on our U1300, Om-366A turbo with faster axles (ex-fire truck) and overdrive, we moved our Alaskan camper to an LMTV and eliminated the breakdown concern.

But I miss the 14 mpg of the mog compared to 6 for the LMTV.

Best solution: get a Unimog, a lightweight shelter, and slow down.

Click to expand...

Thank you @tennmogger ..
I definitely want to keep the habitat lightweight. The LMTV/FMTV's are twice the weight of the other 2 I'm looking at before adding a camper/habitat.
I like that the U1300L (NA) and the MAN G90 (NA) are triple locked. Without spending a ton on portals from Jay Couch, and slowing down as you mentioned, is the OM352 NA with fast axles a good rig for expedition? Cruising at 55/65 would be nice. I don't need a fast rig, just a capable one.

Unimog 1300s have been very popular for off road camper conversions. I would suggest getting in contact with George at Unimog Center in NH as he has imported a lot of them. I am unsure how active he is these days. The German military versions are fairly stripped for a Unimog and that includes lacking an overdrive. Many folks just start with a ambulance box, It is very well built but the ceiling height is about 6 to 12" too low in order to make it able to be flown on cargo aricraft. Folks have raised the roofs, I think there are a few You Tube videos on that process. The trade off with the box is its heavy, it was designed to be occupied during travel and possibly to be removed for fixed use. BOxes made out of composite are going to be lot lighter. George brought in some "end of run" ambulances that were the last made when Mercedes was ramping up for newer models. They are mostly a 1300 but have a beefier transmission. Some folks prefer to bring in former municipal ambulances as many (but not all ) have Overdrives. There also may be a difference in tariffs) I am unsure why or how, but many of the municipal units I see have the OM 352, instead of the newer OM 366 engine. ODs can be bolted up to any ex German army 1300L unless it has been fitted with front PTO shaft. I saw discussion recently that the OD is up to $15 K plus shipping and add un money to have the driveshaft shortened.

The ambulances used a dropped rear floor which marginally drops the center of gravity about 4 or 5 inches compared to the cargo bodies which have flat floors. The wheel arches on the lowered floor of the ambulance intrude in the compartment under the stretcher racks. I think most builders use an Atlas Subframe built by a third party German firm, that is far lighter weight than the OEM mercedes platforms and i think it has the lower floor height. BTW, due to the Unimog flexible chasis, the box has to be supported off a intermediate suspension or otherwise it would get twisted the first time it went off road.

The portal issues can be managed, Vons Mogs builds a tubing adapter that bolts onto the portal fill ports to keep any liquid that may try to escape via the portal air purge system routed back to the portal. Synthetic lubricants also assist in portal life. The key thing is keep them filled. The ultimate fix for the portals is go with heavier duty axles used in the later series 1350 (belgium military). Unimogs do get scrapped out in Europe and the heavy axles could be sourced and shipped for a bundle. I expect Atkinson Vos could help you out. The standard axles used on the 1300 are reportedly interchangeable with the SEE axles. There are also folks who have retrofitted temperature sensors on the fill plugs to monitor bearing temps. Keep in mind, the heavier the build the more stress on the Portals. Some of the expedition rigs are quite heavy, probably over the original 2 ton cargo rating.

If you have some time, a person called Bill Caid documented his experiences with a 1300L camper and a subsequent Mercedes truck based camper. Its worth the read. Bill Caid LifeLog

The biggest thing to realize is once you step up to big custom expedition camper, cost is going to be steep. There are several firms (mostly european) that build drop in boxes, plan on 200K not including the 1300L. People build these out of passion, take several trips and then eventually sell them at a loss. I dont care what chassis you use, you will never ultimately get the money spent to build it out of it.

With respect to speed, one thing to factor in is tire design and speed rating. There really are no "road" tires for unimogs, all of the tires offered with adequate weight ratings are off road tires and they really howl at hihgwway speed. The Germans did use a Continental Mill spec tire with center rib and cleated sides that was somewhat better suited to highway use but they have been out of production for a decade. Every other tire I am aware of does not have center ribs and really howl on the highway and tire life is not great (although there are tricks). At best maximum tire speed rating is just under 70, so even with an OD, you do not pick up a lot of speed, you mostly reduce engine revs as unimogs are limited by engine redline. They really like to run a bit under redline.

Atkinson Vos will build you a 1300L and they can arrange to get it shipped. They are far closer to the center of the mog universe and have sources for a lot of parts that mercedes no longer makes. Unless you want to believe Jay Couch, there really are no comparable shops in North America.

I wonder if anyone has considered using helicopter or turboprop transmission oils in their gear hubs. Turbine transmissions operate at high speed and load continuously.

Recently I was presented with some large bearings that were overheating. Previous operators decided to use high temperature grease (Kendall Super Blue 427) because the bearings were overheating. High temp grease has higher viscosity oil
. This led to more overheating and bearing failures. The solution for sustained high speed operation was to switch to a lighter duty grease (Mobil Polyrex EM)

Thanks @peakbagger !
I wanna keep her lightweight and go anywhere. I have Starlink for the times that I’m out too. Have had that for about 1.5 years.
Cruising back roads, staying off the interstate, and being on dirt/4x4 trails as much as possible is the goal. Yes, there are other rigs out there but I’m pretty set in my mind.
Fast axles, maybe super fast, and overdrive, coupled with a turbo’d engine is what I think I want. Unsure on the super fast.
I’ve been chatting with Paul at Atkinson Vos.. Good guy!

flatwerx said:

Thanks @peakbagger !
I wanna keep her lightweight and go anywhere. I have Starlink for the times that I’m out too. Have had that for about 1.5 years.
Cruising back roads, staying off the interstate, and being on dirt/4x4 trails as much as possible is the goal. Yes, there are other rigs out there but I’m pretty set in my mind.
Fast axles, maybe super fast, and overdrive, coupled with a turbo’d engine is what I think I want. Unsure on the super fast.
I’ve been chatting with Paul at Atkinson Vos.. Good guy!

Click to expand...

I have bought a few large items from AV over the years, like soundproofing mats and a used cab tilting jack. Both came by air freight (not cheap) but they were willing to do it. With all the goodies you want, it makes sense for AV to source a base truck, recon it and install all the parts and ship it over instead of trying to get the parts shipped. The one caveat is that 1300Ls are not immune to rot and the german's use road salt, with what you are looking at for a build, I would fly over to see the donor truck before the rehab. See if they can source the Atlas subframe. BTW, make sure the engine you buy has the oil squirters that spray oil up under the pistons. I think the OM 352 block has to be machined for them but the OM 366 is at least machined and many have them OEM.

I bought my OD from EI, he had supplied it to someone and it was never installed so he bought it back and resold it to me. There were rumors that a mog owner that had installed a Laycock overdrive was working with Gear Vendors (who has rights to the Laycock design) were going to come out with an adaptor but never heard if they did. The mog owner (on Benz world) has had good luck with his custom installation. They are cheap compared to the Claas units.

87cr250r said:

I wonder if anyone has considered using helicopter or turboprop transmission oils in their gear hubs. Turbine transmissions operate at high speed and load continuously.

Recently I was presented with some large bearings that were overheating. Previous operators decided to use high temperature grease (Kendall Super Blue 427) because the bearings were overheating. High temp grease has higher viscosity oil
. This led to more overheating and bearing failures. The solution for sustained high speed operation was to switch to a lighter duty grease (Mobil Polyrex EM)

Click to expand...

I think a lot of approaches have been tried and the solution is stock weight synthetic oil filled to the brim (or even slightly overfilled) with Vons special tubing to recover any oil that tries to go up the purge tubing. If the oil is in there they seem to do well but eventually there can be rear seal leakage and once that starts, there just is not a lot of fluid to leak before the damage occurs. Most folks carry a cheap IR gun and check the temps of the portals at every fuel stop.

peakbagger said:

I think a lot of approaches have been tried and the solution is stock weight synthetic oil filled to the brim (or even slightly overfilled) with Vons special tubing to recover any oil that tries to go up the purge tubing. If the oil is in there they seem to do well but eventually there can be rear seal leakage and once that starts, there just is not a lot of fluid to leak before the damage occurs. Most folks carry a cheap IR gun and check the temps of the portals at every fuel stop.

Click to expand...

Appreciate the knowledge!
What are good temps for the portals? I read some people using cassette seals on the portals.

I’m talking with Paul about a U1550L (366LA) fire truck. Checking if it has fast axles and OD.

I have not seen a hard limit. I have seen 40 to 50 degrees over ambient. I think the difference between each portal is just as important as its likely that a leak would only be on one portal.