gearbox ,fwd seal replacement
GEARBOX,FWD seal replacement
 
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On this page I will try to explane how to replace the fwd outputseal from the
gearbox.
As you can see on the pictures, I was lucky to have acces to the original unimog special tooling , wich is designed for this
repair

because of this it was quite an easy job and if you know wat to expect it should be posible to do it in one day.
I like to take it easy( 2 days.)



I think the parts catalog calls it a control rod.


the rod should be disconnected to be able to roll the axle fwd .
the rod is the only thing that keeps the fwd axle from swinging from left to right while driving.



this is where it all must happen.


after a 70 km drive the mog was leaking 1 or 2 drips every second , at that time the tube to the fwd differential was already
filled.
the oil in the tube will eventually end up in the fwd diff (check oil level of fwd diff and you know if you have output seal
leakage).
previously I desided that I would leave the leakage for what it was untill it was dripping on the ground,I diddn't mind draining
the
diff from time to time .
I put thicker oil in the gearbox to reduce leakage ,but as described above,at a certain point it diddn't help anymore and
repair was unavoidable.



Here you can see the housing removed.
before you loosen the housing, disconnect the fwd axle springs,the control rod,the diff lock rod(gearboxside) and the brake
line T-piece on the fwd diff.
also remove the brakeline connection retaining clip on the cardan(take your pliers and pull out the plate ,the brakeline can
now pass up an down the hole as required.
if you just loosen the bolt in the T-piece(on fwd diff) and bend the clips which hold the brake lines on the fwd axle, you
will not have to interupt the brake fluid system.
make sure if you deside to work this way,that you put chocks 10cm in front of the fwd wheels.
this to prevent the line from snapping when you pull the axle fwd and away from the gearbox.
also be aware that the axle is very heavy and that it will fall down after the last bolt of the U-joint (inside the housing)has
been removed.
so make sure its supported!
IT IS VERY IMPORTANT,that ,when you reinstall the U-joint ,you put the housing already 3 cm from it mounting position,and
put the 2 bolts located between housing and gearbox already in the housing .
if you don't do that you will have to start all over because the housing can't get past the gearbox.

I received a tip from someone who has performed the repair,he says it is a little bit easier when you remove the plate (lid)
from the side of the gearbox
to provide a bit more space.


Here the plastic piece that functions as outer bearing half is removed,its posible to bend it open but be carefull that it won't
break!


Its a bit hard to see but here the tool for loosening the nut is installed
(toolnr401589000700),its a tube with a castelated shape on the end to fit the nut.
you can also see the long arm atached to the tool to apply huge torque.
before installing the tool and loosening the nut ,bend away the the lock washer from the nut.


After the nut has been removed ,you need to get the lock washer out , it might take some time (I did it with two small screwdrivers).
now the puller can be installed (toolnr401589013300),it will pull out the flange where the U-joint was mounted on.(inner flange)
with the original tooling ,you first screw a bushing on the thread where the
nut came off.
that bushing is used by the puller to push on.
the puller is atached to the mentioned flange by 4 bolts.
you better put some bolts into the holes from the housing (outer flange)
before you start pulling,otherwise you will not only pull out the (inner) flange .
you end up with a still assembled part of gearbox.



here the flange has been pulled out but the bushing (part of tool nr401589013300)is still on the gearbox output shaft.
you can also see the temporary installed bolts in the outer flange.



when the U-joint bolts are loose and the axle is tied up to the chassis you can pull out the U-joint and a piece of shaft
out of the axle.
you dont have to but if you want to check the joints condition it might be handy.
after the flange has been removed I removed the 1cm thick plate wich keeps the seal and the bearing.
you can see it next to the joint.
it is sustained by 2 countersunk screws.
on the lower picure you can see toolnr4015890091, it has been designed to put the 1cm thick plate on and put the new seal in.
I did remove the bearing from the plate first to have the old seal removed easier.
removing the bearing is not a big deal.


The U-joint is lubricated by the gearbox oil thru the hollow bolt in the end of the shaft sticking out of the gearbox.
This hollow bolt contains a piece of felt to reduce/regulate the amount of oil flowing to the U-joint.
On the picture you might be able to see there are 2 holes in a ,kind of canal,
on the inner surface of the U-joints flange.
thrue these holes oil is directed to the U-joints bearings.
seems logical that a oil tight connection between the flanges is neccesary!



thanks to eric for lending me the unimog tooling.
thanks to frans for all the info and additional tips and tools.
these are the lockplates wich are used to lock the 6 or 12 bolts from the U-joint to gearboxflange connection.
I used them again when I assembled it again but maybe it would have been better to install new ones p/n 99.2905.1012.00




nice jack ,don't you agree?


Of course it is too dangerous to have just the jack holding the mog up so I used 2 axle stands.
(if they can carry a scania and a mog 406 ,they must be able to hold the 404).
during the repair the stands where used as a pivot point when the front wheels needed to touch the ground or when they needed
to hang clear.



the axle stands


Thats what I call accesability, take your camping chair and take place!