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"Modification of the 4-wheel-drive transmission case"


Just a short report about the places we have been visiting whilst a short trip before Easter. We preferred to be not too far away from home because our son stayed on his own at home and in a case of emergency we wanted to be able to be back quick. Because Anita forgot to take her camera we don’t have any pictures:

Monday, 10.04.2006: Bad Kreuznach – Sarreguemines (Shopping) – Bitche

Tuesday, 11.04.2006: Bitche - La Petite Pierre (Site Seeing: houses in the rocks) – Saverne (site seeing) – Wangenbourg – Nideck – Oberhaslach – Schirmeck – Le Struthof

Wednesday, 12.04.2006: Le Struthof - Kaysersberg (Site Seeing) – Colmar  (Site Seeing) – Rouffach

Thursday, 13.04.2006: Rouffach (Site Seeing) – Muhlhouse (Car Museum + Site Seeing) – Pulversheim (Ecomusée)

Freitag, 14.04.2006: Ecomusée Besichtigung– Selestat (Site Seeing) – Mackwiller

Saturday: Mackwiller (roman temple) – Sarreguemines (Shopping) – Bad Kreuznach




Modification of the 4-wheel-drive transmission case (4-WD-TC) VG500 to a separated 4-wheel drive from reduction and blocking


Unfortunately Mercedes has rated all documents with a copyright, so I cannot publish them here. Who still needs them: I have got copies available, which I can “loan” upon request. Besides that I hope that the photos and explanations are sufficient. Thanks a lot to Pirx (Klaus Petermann) for all his detailed and helpful information, which I am using here.


“Why the heck is he doing that?“ some of you may ask. Well, most of the trucks of this type the 4-WD is activated by a pneumatic switch and simultaneously the transmission is reduced plus the blocking between front and rear axle. For heavy terrain this may be OK but for many cases the normal 4-WD is sufficient – but WITHOUT loosing top speed! On the other side a reduction of transmission can be helpful for fine manoeuvring. But if on ground with good grip 4-WD and blocking of the axles is activated as well this can cause a lot of wind-up in the components, up to severe damages.


The “normal” gear-scheme of the 4-WD-TC is as follows (Note: the numbers refer to the pressure-connections in accordance with the numbers specified on the papers from Mercedes):


Reduction and blocking plus 4-WD connected, 11 & 13 bridged by tube

Street-use:                     11, 12 & 13 depressurized     --------------

Neutral:                           --------------                               11, 12 & 13 pressured

4-WD:                            12 depressurized                    11 & 13 pressured


When adding another pneumatic switch the above scheme can be changed. The pneumatic switch is identical to the one for the differential locking of the rear axle. The Reduction and blocking plus 4-WD connected, 11 & 13 bridged by tube

Street-use:                     12 & 13 depressurized           --------------

Neutral:                           --------------                               12 & 13 pressured

4-WD:                            12 depressurized                    13 pressured

Additional pneumatic switch:

Front axle engaged:       --------------                               11 pressured

Front axle disengaged:  11 depressurized                    --------------


Where do I find the connections? (Please refer as well to the photos further down!)

Connection 11 is on the front side of the 4-WD-TC, on the right hand side – seen in the driving direction. (In the original version here is a double air-hose connection which bridges to connection 13.)

Connection 12 is on the front side of the 4-WD-TC, on the left hand side – seen in the driving direction. (Here is as well the “original 4-WD-indication light.)

Connection 13 is on the rear side of the 4-WD-TC, on the left hand side – seen in the driving direction.


All required parts were till 2006 still available from Mercedes directly! Most of the items can be organized easily from a well equipped spares dealer, e. g. the hoses (Tecalan 6 mm, 10 meter is more than enough) and the pneumatic switch 001 997 5036 I got from a dealer for second hand parts much cheaper (original part 2006 approximately EUR 65 incl. VAT) which is identical to the pneumatic switch of the differential locking of the rear axle. The symbol for the pneumatic switch can be ordered by Mercedes under part-# 385 584 4324 for approximately EUR 6,-. Who wants to have an indicator in the dashboard should go for new parts from my point of view because these items don’t last that long. The “pneumatic activated light-switch” (e-switch) is connected by putting a T-hose to connection 11.



In the base-plate of the drivers-cabin are directly next to the switch of the differential locking of the rear axle 3 (!!!) more pre-drilled holes for switches. They can be seen when the drivers-cabin is tilted to the front. The holes are simply sealed by a plastic cap. So if you cut off the noise protection foam from underneath you can easily push out the plastic cap and than you only have to cut out the hole from the floor layer. Afterwards the pneumatic switch can be fixed easily.


The supply of pressurised air should only be from a hose, which is behind a safety valve. Otherwise a possible damage to the pneumatic supply for the transmission could cause loosing air required for the brake system! I have taken the air from the “rear-axle differential lock” by putting in a t-connection.


Then you need to pull a hose from the pneumatic switch to the 4-WD-TC. If you want to have a light indication in the dashboard as well you should add a double wire from the dashboard to the 4-WD-TC.


As already mentioned remove the double air-hose connection from 11 and connect the pressure-hose to 13.



A phot showing various spares: Electric Connector, Pneumatc Switch, T-Connection plus several parts for connecting the pressure hoses.



The new Tecalan-hose connect now to 11. If you want light indication put the T-hose in between and fix the e-switch to the one side, apply the connector and connect the cables.



For the dashboard you need a light-tray (I had a spare one from the formerly top-mounted yellow warning lights) plus an indicator-cover, which fits respectively which suits you – that’s it. I am now using the original red light for "front axle added" (to match the symbol of the pneumatic switch) and the additional white light for the blocking & reduction.



Mercedes has a number for this optional version, which includes all parts: SA 25 370. Only the light-tray and indicator-cover are not included.


Just in case that someone from you has the 100% fit indicator-cover order-# from Mercedes – I would appreciate very much your notes!

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Stand: 24. September 2010