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Spezial-Forum zur Unimog-Baureihe U 404 S.

Moderatoren: stephan, krahola

Hi...new in forum.

So long story short...I receive message from space that I need 404 Unimog....and after month in research, I'm a happy owner of 1964 fire truck, which in some moment probably was converted to kipper.

The odo shows 28 550 km.
It has front PTO.
Kipper is probably from small truck with electric pump...not finished.

I have the truck from a week. I was more or less prepared that this truck is 60 year old and there should be some work done on some places....but not i such scale.

Have some experience with old vehicles ...but this too retro :sweat_smile:

I'll need some advices in the process, so fill free to help :respekt

SO...what I have done.

Fuel system

It's a complex one...two tank-selsctor -mechanical pump- electric pump. I decide to simplified the system:
- so I leave just one tank,
-make aluminum flange on place of electric pump whit suction, return and vent line
- place a fuel sender on place of old return line
-make a custom bracket with fuel filter and low pressure electric pump
-put a new fuel line

some how works...need more modification

24 to 12V

it's appear that 24V system is pain with the parts...everything is hard to find. I took a decision to switch to 12V system.

For now:
- I throw out the Generator with regulator and starter.
-Put a 12V starter...spins good.
- new + line between starter and some distribution joint

...need to source some old school alternator and to adapt it...and of course to change some bulbs. Blower and wisher will work at half speed...forever ..don\ plan to play with them.

Air system

too complicated...with air brakes for trailer

I cut it complete out.


Should solve problem with brake booster, as far as I remove compress air system

Zuletzt geändert von Andrey Nikolov am 09.04.2024, 16:18, insgesamt 1-mal geändert.
Welcome Andrej, (is this correct?

we use always sign all our comments with our first name at the end.

You have a nice project.
If you need any help you are free to ask for it.
But in case try to describe the specific problem as exact as possible.

Best regards
Hello All,

google translate version

Vielen Dank für die Begrüßung.

Soweit ich mich damit befassen muss:


Kann ich nur die Zündkabel durch alte Stecker ersetzen (der Teil, der mit dem Verteiler verbunden ist)?
Gibt es ein fertiges Kit im Angebot?

Ich habe vor, einen Transistorzünder/-kollektor zu verwenden.


Ich möchte ein Vakuum-Booster-System nutzen ... Ich recherchiere einige Optionen, aber es gibt große Probleme:

- OEM-Booster – schwer zu finden, nehme ich an?
- Der Hauptbremszylinder des Unimog ist etwa 32 mm groß, der größte, den ich finde (VW LT oder Boxer usw.), ist 25,4 mm. Also definitiv nicht genug Volumen.
- Der Bremspedalweg des Unimog ist klein – weniger als 30 mm (die mechanische Untersetzung des Pedals beträgt 7:1 ... die meisten Fahrzeuge sind 5:1) ... also nicht genug Weg

Thanks a lot for welcome.

As far as I have to deal with:


Can I replace just the ignition cables using old connectors (the part with is connected to Verteiler)?
Is there a ready kit on sale?

I plan to use some transistor ignitor/commutator.


I want to go vacuum booster system ...I research some options, but there is major problems:

- OEM booster - hard to find I suppose?
- Unimog main brake cylinder is around 32mm, the largest that I find (VW LT or Boxer etc) is 25,4mm. So definitely not enough volume.
-Unimog brake pedal travel is small - less then 30mm (mechanical reduction of pedal is 7:1...most vehicles are 5:1)...so not enough travel

Zuletzt geändert von Andrey Nikolov am 09.04.2024, 16:19, insgesamt 2-mal geändert.
Hello Andrej,
the ignition sparks, cables and the ignitiun distributor are a little special as all is shielded. But it is possibly to change this partly so you can use normal unshielded sparks and cables. You only hve to rework the distributor side of the cables.
See the pictures on the right: https://www.unimogfreunde.de/technik-ti ... ndkabel404

I still fight with brakes, electrical system etc.

Electrical system

I was able to change almost all bulbs to 12V and now I focus on creating rea lights...blinker, stop stand and rear. Original, it was just two tailer 7 pin connectors, so I remove them and put instead some old school BOSCH taillights. For now Blinker and standlichte are working and I just should solve the wiring of stoplight and reverse light

...so question:

I see some cables come from the gear levers...I pretty sure one is PTO switch ... I hope the second switch is rear/backup light? Can be?

Main question...Servolenkung on 404

I read a lot of post here and there....I even bought 406 Lenkgetreibe (it's a beast, maybe 50 kilos), but I think is not easiest swap.

I read that there is 3 times touch form the God... holly 404.0 Lenkgetreibe ...but this should be very rare.

from MB100 with some modes or G wagen ?

Zuletzt geändert von Andrey Nikolov am 09.04.2024, 16:19, insgesamt 1-mal geändert.
Hi Andrej,

the stoplight switch is on the backend of the brake master cylinder.
A reverse light was not installed on my 404 but you can test the cables with a small lamp connected one side to ground and other side to the cable to test. Than switch PTO / Reverse Gear etc.

On my 404 I had the 406 power steering installed. So this conversion is possible but some changes has to be done.
Hello All,

Tonight I was able to bleed out to some point the brakes...pedal become very stiff.

So question:

When I research the brake system variants on 404, there was at least 3 types:
- no booster
-with vacuum buster
-mit Druckluft, eigentlich wie meine.
- and maybe fourth variant - Druckluft just for the trailer and no booster.

I doubt that I'll load something heavy, but with my current set up - no booster, pure foot power....can Unimog brake ...let's say 'Satisfactory'???

Zuletzt geändert von Andrey Nikolov am 09.04.2024, 16:20, insgesamt 2-mal geändert.
Hello Andrey,
up to a total weight of 4750 Kg the 404 had normally no booster.
With a higher weight a brake booster was nessecary.
If the 404 had no kompressor in that case the vacuum booster was used. Otherwise as the kompressor was available the compressed air booster was used. On fire trucks 404.0xx this variant was normal.
Hello All,

Finally rebuild kit for the carb arrive (delay due to Estern....our is a month later..strange). It's cleaned via ultrasonic, new gasket installed and acc. pump renewed ... aaaaand I lose the spark. When manually ground the braker, coil is sparking, but some how not distributing...damm, first ride is no go again.

Zuletzt geändert von Andrey Nikolov am 09.04.2024, 16:20, insgesamt 2-mal geändert.
Hello Andrey,

is the breaker contact well installed. It need a opening gap of 0,3-0,4mm.
And is the distributor finger correct place. I had the same issue years ago. Had to change the breaker contact. In the hurry I forgot to put the distributor finger back in the ignition distributor. Shit happens sometime
Hello All,

I deal with kipper hydraulic. It is 12V, its work good. I make a new power wiring and even small remote with up/down buttons....some kind of distraction of the problem with ignition. Anyway i notice there is spark just before starter start turning and when I release the button. I measure the voltage drop and it\s a severe 7-8 Volts. At the battery is just 10,5V....so a lot a drop thru 60 old electrical system of Unimog...probably 12V conversion helped a small.

I wonder should I put some Ignition relay directly from battery thru some fuse

Zuletzt geändert von Andrey Nikolov am 09.04.2024, 16:20, insgesamt 2-mal geändert.
Hello Andrey,starts tuning
Where you see a spark just before the starter starts turning, the ignition is only working and producing sparks if the motor and the ignition distributor is turning.
Where you measure the voltage drop?
When is the battery voltage only 10,5 V?

The normal 404 wiring has no ignition relay. The ignition current is directly routed from the ignition switch. You can use a relay but any additional component is a possible point of failure. As the 404 was mainly a military truck all electric is kept as simple as possible. If you have a large voltage drop across the wiring it means mostly that some contacts are corroded. So general it is better to find this points and rework them as to build work arrounds.

Just my oppinion
Hello Jurgen,

So general it is better to find this points and rework them as to build work arrounds.

You are completely right....I'll check some points, for now it's not clear where exact main '+' cable goes. I connect existing '+' to starter solenoid , then '+' is going to some connection that are covered with double plate. Checking the diagram probably goes:
- simultaneously to main switch and some kind of dynamo/generator cut off relay .. probably this relay cutting power to dynamo till it's not start to charging???
- from cut off relay again to .....main '+' line

I should remove this plate which cover the wiring....but this means to rework entire electrical system
I even bought a modern fuse holder with blade fuses.

But it looks like a lot of work and I'm very slow with this stuff (during the years a convert couple of bikes to EFI and turbos and it take me a lot time to set up wiring... with lot of goes and backs)

Zuletzt geändert von Andrey Nikolov am 09.04.2024, 16:21, insgesamt 2-mal geändert.
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