unimog 404 trolfs

UNIMOG 404 S Overview


Unimog 404 Specification Overview

The 404, or "Unimog S", is perhaps the most common Unimog among enthusiasts, especially in the USA. They tend to be the most affordable and have acceptable on-road characteristics. 404's (Unimog S) were built primarily for various armed services from 1955 until about 1973 as 404.1 and from 1971 to 1980 as 404.0 aka U82 - U110.

There are two major types of 404, aka "Unimog S", There is the 404.1 and the 404.0. The 404.1 is by far the most common and was primarily built for various armed forces, including the German, Swiss and Belgian armies. The 404.0 is much less common and was built primarily for the civilian market. It has a more modern cab which is a big improvement over the original 404.1 cab. The 404.0 also had options which were unavailable on 404.1's, notably a larger 2.8 liter engine and power steering. The frame, gearbox, axles and suspension are the same on both the 404.1 and 404.0.

Unlike other Unimogs which are diesel, 404's are powered by six cylinder gasoline engines. The 404.1 are powered by the M180 82 hp 2.2 liter engine while the 404.0 are powered by the M130 2.8 liter engine which produced 110 hp. These engines are based on Mercedes-Benz automotive engines, and other than some different specs and add-ons, they are essentially the same as the engines found in the old 220 or 280 sedans. As a result, parts are available and there is upgrade potential with these engines.

The 404's have a 2900 mm (114 inch) wheelbase. The drivetrain consists of a six speed forward, two speed reverse gearbox, coil suspension, portal axles, locking differentials and shift on the fly 4x4. There are a lot of variations between various 404's but for the most part, they all have the same engine and drivetrain configurations and wheelbase. There were short wheelbase French versions and diesel versions for Angola but these are both very uncommon.

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The 404 comes in many configurations including a dropside pickup (Pritshe), or with various types of enclosed rear bodies (Koffers) originally for radio vehicles or ambulances. The 404 was also converted into several types of fire engines with various cab and rear configurations.

The two door soft top is the most common cab configuration although two door hard tops and four door (DoKa) soft tops were also produced. Unimog 404's were built for various armies and for each country there were slight variations. For example, Swiss Unimog 404's have circuit breakers, German ones don't. However, many German Army 404's come with an auxiliary air brake system which includes a heavy duty engine driven air compressor which is handy for airing up tires on the trail. Belgian and Swiss vehicle normally don't have this feature. The 404.1 is probably the most "standard" Unimog, and German, Belgian and Swiss 404's are all very similar.

The 404.0 is the updated version of the 404.1 and has a more modern cab which is very similar to the U900/406 cab. Also the more powerful M130 engine was available as an option on the 404.0, hence the U110 sales designation. However, 404.0 were never built in the numbers of the 404.1 and are uncommon, especially in the USA. As a result 404.0 are more expensive and harder to find.

Unimog 404 General Overview

The 404 makes a great starter vehicle for somebody interested in Unimogs. They are the cheapest type of Unimog, are capable of 60 mph, and are extremely capable off-road. They come stock with all the features serious off-roaders want, including awesome articulation and ground clearance, low gear ratios and locking differentials. Furthermore parts are readily available and they are shade tree service friendly so anybody with reasonable mechanical skills can maintain a 404.

Off-road, the 404 is truly impressive. Few stock vehicles even come close to a 404 off-road and nothing the big three has made even comes close. The 404 has all the ultimate ingredients for truly awesome off-road capability, including unsurpassed ground clearance, an extremely flexible suspension, crawler gearbox ratios, locking differentials and a virtually bulletproof drivetrain. Because the 404 was engineered by Mercedes-Benz with these features as standard, Unimogs don't break on the trail like most heavily modified 4x4s which were never intended to run big tires, crawler gearboxes or diff locks.

On first impression, the 404 may seem big, especially compared to Land Rovers, Jeeps, etc. However, it is actually quite nimble and actually has a tighter turning radius then a Land Rover D90! Obstacles that seem huge in most 4x4s are just minor bumps for a 404. Finally, 404's are also just plain fun to drive on-road or off-road!

However, there are a few things to be aware of with the 404. They are spartan, and the interior is drafty and loud. If you drive a modern vehicle you might be in for a shock. The 404 is in the same league as an old Jeep or Land Rover, albeit a bit louder and a bit slower. Which brings up top speed... Despite what some may claim, stock 404's will not happily cruise down the highway at 60+ mph even though they maybe able to achieve that speed. Due to the low gearing and low horsepower, 404 Unimogs are really good for about 45-50 mph sustained cruising speed. They will go faster than 50 mph, but they will really be screaming and once you come to a hill, they will slow down pretty quickly. While this isn't a serious issue for someone who is primarily using a 404 as an off-road vehicle or as a hobby vehicle, it does limit their suitability as expedition vehicles or daily drivers.

Unimog 404 Improvement and Upgrades

Of course there are ways to improve the 404.1 to make it more suitable for road use. Two issue limit the 404.1-- gearing and horsepower.

Unfortunately there are no overdrives or high ratio gears available for the 404 so to a large degree the top speed is limited regardless of horsepower. However, 12.5R20 tires fit on a 404 and will bring the theoretical top speed up to 70 mph with a realistic (but loud) cruising speed of 55 mph. However, with the standard engine, the Unimog will struggle to maintain the higher speeds and the need to shift down on hills will increase. As a result, larger tires only give good results after the power has been increased to cope with the higher gearing.

With the standard M180 2.2 liter engine there are some areas for power improvements:

  • Upgrade the ignition using an 12v volt Mercedes-Benz automotive distributor, high performance ignition wires, a Pertonics unit and 12 volt spark plugs. This will make the engine much easier to maintain and diagnose, and will also slightly improve power and drivability. If the 24 volt system is retained, the Pertronix unit is available in 24 volt as well and is a highly recommended upgrade which provides more reliability and improved ignition performance. Upgrading the ignition system will give more reliable and consistent performance and help the engine reach it's full potential. However, actual horsepower improvements will be minimal unless the ignition already had problems (which is often the case).

  • Use higher compression heads from M180 automotive engines. There is really no benefit to using the low compression setup found on the Unimog. It was intended for use with very poor fuels (60-70 octane rating) often used by armies in the 60's. However, unless you plan on driving extensively in under developed nations, the low compression engine offers no benefits and saps power and efficiency from the engine.

    Upgrading to higher compression heads, either by modifying the original heads or installing automotive spec heads, is a relatively easy and straight forward modification that will improve the power and fuel efficiency. To realize the full potential of the high compression head, the ignition and carburetor should be tuned to match the new specs. The power gains from this modification will be noticeable and are worth the effort but they will not be a dramatic improvement that fundamentally changes the driving characteristics of a 404 - it will still be slow but a bit more drivable.

  • Upgrade to a M130 2.8 liter high compression engine
    In order to get a major increase in power, without radically modifying the entire vehicle, it is necessary to upgrade to a M130 2.8 liter engine. These were used on many Mercedes cars and can usually be found in junkyards. A rebuilt M130 with a good ignition and a well set up carburetor(s) will dramatically improve the performance of a 404, and with 12.50 tires it can actually achieve acceptable on road performance although it will still be slow by modern standards. Gas mileage should improve too, especially if Weber carburetors are used. Contrary to popular belief, many versions of Weber carbs do quite well in off-road situations and can tolerate off-road angles as well as the stock carbs - plus they don't leak like the originals!

    Various American V6's and V8's as well as various European petrol and diesel engines have been shoehorned into 404's with varying degrees of success. Anything is possible with enough time and/or money. However, don't count on the job being cheap or easy and the results are unpredictable. Also, even with lots of horsepower, top speed will not improve. If you want a lot more power than the 2.8 liter engine provides, you should probably consider another vehicle.

Unimog 404 Diesel Conversions

Finally there is dieselization of the 404. The 404 is the only Unimog that is not a diesel. Mercedes did build a limited number of diesel 404's but they are very rare. They were also pathetically slow due to the fact that they used the 2.4 liter naturally aspirated diesel. There are aftermarket kits available to swap in Mercedes or Peugeot diesel engines. Various Mercedes diesel engines, from the 2.2 to 3.0 liter engines, can be retrofitted into a 404 with these kits. There are some great advantages including better low end torque, better fuel economy and more reliability. The Mercedes units in particular are excellent engines and diesels in general are more suitable for serious off-road use. The drawback is that top speed will be effected and unless the 3.0 engine is used, the 404 will be even slower. By diesel standards, the Mercedes diesels are high revving engines. However, despite this, top speed will be limited due to the fact that regardless of horsepower, these engines can not run at as high RPMs as the gasoline engines. The 2.2 and 2.4 diesels do not produce enough power to make a 404 practical for road use and even the non-turbo 3.0 will slow a 404 down. The 3.0 turbo makes a great conversion and acceptable road speeds are possible with 12.5R20 tires but this engine is a tight fit in a 404 and the turbo intrudes into passenger legroom. It is also a complicated engine swap although there are some very good kits available.

For somebody who doesn't have a Unimog and who wants a diesel, buying a 406 or 416 makes much more sense than upgrading a 404 to diesel. The 406/416 costs more initially but will probably end up being a lot cheaper after a 404 conversion is completed. Furthermore, the 406/416 are much better vehicles in other respects and open up all sorts of other possibilities that are impractical in a 404. For those who already have a 404, a Mercedes 3.0 turbo is a great conversion and improves a 404 in almost every respect. However, it is not a direct swap and can be expensive.

Two common options on a Unimog 404 are the PTO and crawler gearbox. If one is fitted than the other can not be fitted since they attach at the same place on the gearbox. The reduction gearbox allows for two additional low gears, giving a crawl ratio of almost 350:1! The PTO allows for a front or rear PTO shaft and is commonly used for the Mercedes or Werner front mounted PTO winches. These winches are substantial units that can be used continuously under full load and make normal "heavy duty" electric winches look pretty pathetic. The PTO can also be used to power pumps, generators, etc. However, unlike other Unimogs, the 404 was not really intended to take a wide variety of implements. As a result, it does not run hydraulics and the PTO system is limited so there is not a large selection of "off the shelf" implements designed for the 404. If running agricultural implements is a priority, then a 406 or 416 would be a more practical and useful vehicle.