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Description of the
Ventilation System of the front intermededia gearbox

The HPH-VENTILATION no. 8001 is for the front axles of the UNIMOG with the

nos. 737
.1xx  737.2xx and 437.5xx

for the rear axel is the Ventilation set 8001HA

nos. 447.1xx  347.3xx and 347.5xx

This concerns the Unimog models from 406 up to 437

For the front intermedia gearboxes of the axles version 737 --- the outflow of the oil is possible via the ventilation system from
the front intermedia gearbox to the axle tube and further on to the differential. 

This concerns the above mentioned axles of the Unimogs with 6-hole—rims and axles from 406 up to 437.

This is particularly the case for longer and faster drives on motorways and the therefore higher temperature of the oil.
The higher the speed is to be driven, the higher is the temperature of the oil and all the more oil flows into the axle tube.
That is why the front intermedia gearboxes loose oil and get damaged.

On my Unimog after driving 1.000 km on the motorway (90 km/h) 50 to 70% of the oil had flown to the axle tube.
When driving fast on a motorway too little oil can be in the intermedia
gearboxes already after 500-700 KM.

Which effect has the HPH-VENTILATION system with compensating reservoir?

By the now modified ventilation system the rising oil mist condenses in the compensating reservoir
and the oil flows directly back to the intermedia gearbox and is not pressed further into the axle tube.
 In this way the loss of oil from the intermedia gearbox is minimized.
Even after 5.000 km there was only a small loss of oil
with the integrated ventilation system with compensation reservoir.
It was less than 10% at my front intermedia gearbox in my Unimog 435.


The assembly is practicable without change.
All necessary parts are included in the mounting kid
including seals and hose clamps.



Unscrew hollow screw 3. of the original existing ventilation system (wrench size 12) and remove the ventilation tube from the hose 1. from the top. We no longer need the tube, only the hollow screw.

Unscrew or turn off the bolt 2.
with a spanner no. 19.

Turn off filler screw 4.
We do not need it anymore.

Take the new ventilation system and insert the screw 2.

Place the ventilation system and screw the bolt 2.
But do not thigten the screw now.
Maintain mobility of the ventilation system.



Equip hollow screws with sealing ring.


Insert hollow screw 4. with sealing ring via ring connection. Then insert the second sealing ring between ring connection and intermedia gearbox.


Tighten hollow screw.
Make sure that the tube  does not touch the screws. Without being too tense.


Position the ventilation pipe / tube 3., insert hollow screw and sealing rings and screw them together. Wrench size 12.

Only now tighten the screw 2. securely.

Connect the upper ventilation pipe/tube with the hose to the axle an tighten well with the hose clamp.

Here the ventilation of the left side was described.

The right hand side is the same.


To order here

Here is on YouTube a video where is to see how it is to do.


Mercedes, Unimog U 1300L U 1700 front axel, reduction gear gearbox oil


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