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404 front axle seal

10K views 25 replies 9 participants last post by  mhame 
#1 ·
I had a front axle seal leaking so a week or two ago so I bought a new seal, bronze bushing and outer retainer washer and installed them. Halfway through my wheeling weekend I start pouring fluid out the same side again. I checked it out and the seal had popped completely out.

I did not have another seal so I drove 200 miles round trip home to grab a spare knuckle that had a seal in it and removed the leaking knuckle. Thanks Thiemen, that spare front axle saves me again! Upon removing the leaking one I found the bronze bushing had slid inboard out of the knuckle which allowed the shaft to drop which destroyed the seal.

This is not the first time this has happened to me after replacing a seal... Is there a special trick to getting the bronze bushing to stay in?

Apparently just pressing it into the knuckle from the inside is not enough... :frown
 
#2 ·
Are you using the special tool that flares the bronze bushing into the housing? Most of the time I do not see people do this.

33-2/3 #18

"Carefully force in new bushing by means of installation mandrel 401 589 01 15 00"

If you've ever seen the factory tool it's quite a work of art.

There are 2 styles of bushing. The very early version where the bushing goes in from the inner steering knuckle side, and the more common later version where the bushing goes in from the CV side. I do not think it is possible for the later version to work it's way into the housing as it is flared....

Picture of New style bushing to be be installed from CV side. The repair manual pictures the old style bushing.......

Axle Bushing

Cheers,

Scott
 
#3 ·
A special tool to flare the end....huh.... yep don't have one of those.

Yeah that one you have a link to is the one I bought from you the other day. So that one goes in from the outside?

The one I removed went in from the inside and it tapped out with a hammer and a large socket pretty easily. Do not recall seeing a flare to it except on the inside that stopped it from sliding outwards. Looked like it jsut pressed in and stayed....
 
#6 · (Edited)
Bronze bushing notes......

This is a difficult one as I cannot find any direct reference to the 4063321050 Axle Bushing's "installation direction" being changed when this bushing superceeded the original bushing. However, for the last 15 years our workshop has installed the bushings from the "outside - In" and have never had a failure.

What is CERTAIN......you MUST "calibrate" the bushing as the calibration process helps to "flare" the bushing in place."

404 Repair Manual - #19 - "Calibrate installed sinter bushing with tool number 401 589 00 15 00 - Fig 33-2/10"
Of note - Fig 33-2/10 Clearly shows the old style "large shoulder" bushing being flaired from the inside out.

Tools Manual - 33B - Application 403, 404, 406, 411 etc.,etc.
Figure 33-0077 - Clearly shows a 404 knuckle with the new style bushing being installed/flared from the Inside Out.

Directly below this figure shows UR33-0630 - A 406/416 style axle with the bushing being installed from the Outside - In.

MB parts systems do NOT stipulate use of 1 bushing "up to" or "as of", they simply show a direct replacement - Old Style for New.

Why does EI install from the Outside In?

#1 - The steering knuckle has a matching bevel perfectly machined at the same angle as the shoulder of the new bushing....From the outside.
#2 - Installed from the Outside in - it is Impossible for the bushing to come loose and work it's way into the axle housing as it is sandwiched between the shoulder and the seal.
#3 - When we install we use "bearing retainer" - Locktite for bearings.
#4 - After bushing install we run the "calibration tool" thru from the outside in.
#5 - If you examine the bushing there is a slight shoulder inside the bushing at the end opposite of the exterior shoulder.. I believe that is designed to capture gear oil and help to work it into the sintered brass. This would only work if it is installed with the shoulder on the outside of the knuckle.

Some pictures and notes below.
 

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#7 ·
In regards to the "calibration tool"

401 589 00 15 00 Replaced by 406 589 02 15 00

One heavy very precisely machined tool. This tool is tapered and gets larger as it pushes thru the bushing. I believe that this is one of the primary things that "locks" the bushing in place.
 

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#8 ·
Wow. That is a tool my wife would be proud of... ;)

Joking aside, where can I get one of those?
 
#11 ·
Hi Guys,

I'll check current availability from MB, I've found quite a few of the 406/416 specialty tools are being discontinued. I do have 2-3 of these available for rent/use. I'll be honest, we are a bit discouraged in regards to tool rental......

Please do not take this the wrong way, but we have a lot of people that are not mechanically inclined trying to do repair jobs that are out of their skill set...IE they shouldn't be attempting. The end result is that we are getting a considerable number of tools broken/destroyed. The problem is, few users that break the tool are willing to accept responsibility for replacement cost......(how do you know I broke it/mis-used it, or the guy prior to me did and I am now responsible.....?) Originally I had priced replacement into the rental. IE I expected to get 10-12 rentals out of X tool and therefore I could replace as needed. The problem hits when we are getting 2-3 rentals before breakage, or 1 use before breakage..... The hub removal tool is a good example of this. To add insult to injury the real let down is to find out the original tool is no longer available to get a replacement.

Anyways, I'll update with MB availability on this tool. I don't currently have a kit for this job, but I'll take a look at what is involved. Normally it would be the tools to do the steering knuckle rebuild at the same time. Alternatively, we do not use the factory puller with this tool as I prefer to do it with the steering knuckle in place.....that requires a bit of a 1 off fixture.

Cheers,

Scott
 
#12 ·
Well if the price is right I'd be interested in purchasing one. I seem to be in an axle seal replacement scenario often and now that a buddy also has a buggy that is running 404 axles my 404 axle workload seems to have doubled :) Somehow though I seem to be the spare parts guy on all our adventures.... maybe I should get him to buy the tool ;)
 
#13 ·
Scott,

If they are discontinued and the existing stock is disappearing, can we get some exact measurements on the ones that are still around/in good condition? Those of us with home shops could start making some as needed for repairs. I still haven't gotten around to disassembling my transmission for repair, but at some point I'll need/make the necessary tools.
 
#14 ·
You wanna see cool tools? There's a list of "workshop" equipment for repairing Unimogs. Some/most that stuff you don't actually need, but it's cool to see, they have a Jig for example just for axle repair, to be self made with plans from the plant (by request) for pulling out the axle and holding it up to do repairs, need it? no. Cool? yup :wink
 

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#15 ·
Scott, any word from MB if the tool is still available?

Is this something we to research having some fabricated?
 
#17 ·
Well since we could not find them domestically I went with the eBay find: Mercedes Benz Unimog Axle Special Tool 406589021500 | eBay 3 out of 5 left!

Just got mine today.. I'm out of town till Wednesday so I haven't gotten to mess with it to verify fit and such but the part number was right. Hopefully my wife relinquish it when I get home ;)
 

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#19 ·
I have yet to use mine as the last leaker I had I just swapped the whole knuckle for a spare with a good seal so let us know how it works out. I should order a spare seal soon to get my spare knuckle back in action so I have one with me during the plethora of Mog-Tastic events coming up this summer. I don't want any down time for any reason :)


I don't have the rest of the pusher mechanism but assuming putting it in a press would work just as well.

Those things are almost gone. One left when I looked today...
Mercedes Benz Unimog Axle Special Tool 406589021500 | eBay
 
#22 ·
The few the eBay guy had seem to be gone now. Haven't seen them anywhere else so far. I have yet to use mine I bought on eBay. My Unimog has been on flat and level ground since our move on tractor duty so the offcamber situations that would cause oil leakage haven't happened been a priority for the last few months. :(
 
#26 ·
There is an service information - dated September 1970 - with regard to the special calibrating tool from Mercedes Unimog. The former tool 401 589 00 15 00 (five steps) shall no longer be used. It was replaced by 406 589 02 15 00 (three steps).


The calibration must be by forming without swarf. The sinter metal pockets which keep oil after dipping in warm oil. These pockets shall not be closed by swarf or abrasion.
 
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