3.46 Rear Axle Rebuild

[DavidBrough]

I am in the process of re building a 3.46 axle from a 1971 280SE 3.5 and now need to order some new seals and rubbers and confirm which SL bits will just transfer across. Does anyone know which parts are not interchangeable with the SL axles. I know the wheels bearings are both taper rollers on the SE and whilst the diff casing and internals are different it seems that all other parts should be the same as for the SL i.e. disks, callipers, Diff carrier, handbrake parts, trailing arm mounts, bearing seals etc. Does anyone know if this is correct?

David Brough
1969 280SL Auto with A/C

[ja17]

Hello Davic,

Everything should be the same except the handbrake cables. You will need to get plugs to close the connection for the cooling tube.  Two oil pan drain plugs (14mm allen style) will work nicely. The expensive barrel roller wheel bearing was desinged to be able to hinge along with the axle casting on the right side. I always use one of these on the right side. I have never seen one of these fail. They are very durable. On the other hand I have replaced many standard roller ball bearings on these axles.

Joe Alexander
Blacklick, Ohio

[DavidBrough]

Thanks Joe, it's nice to know for sure. I have already purchased two drain plugs and sealing rings to replace the breather pipe.

David Brough
1969 280SL Auto with A/C

[DavidBrough]

I've now ordered the new parts I need from SLS in Germany and they say the only other difference between the 108 and 113 axles is that the brake caliper pistons are larger in the 108.

David Brough
1969 280SL Auto with A/C

[ja17]

Hello David,

That is new information for me on the brake calipers being different. It would be nice if someone could verify different part numbers for the W113 rear caliper and a 250S (W108) rear caliper so this doesn't keep me awake tonight!

Its nice to know these things.

Joe Alexander
Blacklick, Ohio

[ja17]

Hello David,

I Had to do a little research on the matter of rear brake calipers. It appears that all the W113 cars with disc brakes shared the same rear calipers as all the W108 sedans with six cylinder engines. These had rear caliper pistons which were 42mm diameter. See page 444 of the 1969 Technical Data Booklet.   However the W108 sedans with V-8 engines had rear calipers with pistons having 35mm diameter! see page 452 of 1972 Technical Data Booklet for this information.

Joe Alexander
Blacklick, Ohio

[Naj ✝︎]

quote:Originally posted by ja17

Hello David,

That is new information for me on the brake calipers being different. It would be nice if someone could verify different part numbers for the W113 rear caliper and a 250S (W108) rear caliper so this doesn't keep me awake tonight!

Its nice to know these things.

Joe Alexander
Blacklick, Ohio

113 Rear Calipers (Same as 250S, 280SE...)
000 420 4683 left
000 420 4783 right

280SE 3.5:
002 421 5498 left
002 421 5598 right.

The good news is that the mounting holes on the axle tube should be the same. All use the same mounting plate with the 2 captive nuts: 108 420 0286.

Now, the W100 rear axle - thats something else!!!

Picture to follow.



naj

[DavidBrough]

Work is progressing with my axle rebuild but I think I may have hit a snag. On close inspection I find that the RH carrier race has wear lines on its edges and moves freely in the diff casing and I assume it’s supposed to be a tight fit. On the basis that I have to replace the bearings does anyone have the specification for the carrier bearing pre load and backlash. I intend to get a local specialist to do the work but I would like to be armed with the correct data if anyone has it.

I attach a picture of the bearing race and the large castellated ring nut which I assume is used to apply the bearing pre load to the right hand side with shims to the left hand side providing the correct mesh pattern with the pinion. Dose this sound correct?



David Brough
1969 280Sl Auto with A/C


Download Attachment: Diff Inner Bearing.jpg
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Download Attachment: Bearing Retainer.jpg
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[DavidBrough]

Making continued progress on the axle rebuild but I’m having a bit of trouble with the detail of final set up and torque settings and hope someone can enlighten me.
 
Firstly, I am looking at setting the distance “A” of the diff carrier at 158mm +/-1mm but am not sure where exactly to take the measure as fig 35-5/7 of the BBB shows the measure to the body of the carrier below the machine top locating portion whereas fig 35-5/8 shows the measure to the machined top portion itself. As mine shows a difference of over 1mm between the two possible measures could anyone let me know which is correct.

Secondly I am finding some of the descriptions for the torque settings in 35-0/8 a bit confusing, it states:-

Hex bolts for attaching strut to supporting tube   20mkp
Hex nut for attaching strut to chassis frame      10mkp

I understand the strut to be the cross strut as per photo but this attaches to the diff carrier not the supporting tube and 20mkp seems far too tight for any of the nuts. Does strut mean radius arm in this instance or should the cross strut nuts really be that tight?




David Brough
1969 280SL Auto with A/C



Download Attachment: Carrier35-5-7.jpg
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Download Attachment: Carrier35-5-8.jpg
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Download Attachment: Cross Strut.jpg
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[jeffc280sl]

Figure 35-5/7 shows a reference line from front edge of the machine top extending down through the carrier arm.  I believe thios line is supposed to represent the same location as used in figure 35-5/8.  Any variance can be set when you check the alignment of the axle after mounting.

My understanding of the torque settings is the same.  I hope someone else can help.

Jeff C.
1970 280SL 4-speed

[DavidBrough]

Thanks Jeff, hopefully someone can enlighten us regarding the torque settings.


David Brough
1969 280Sl Auto with A/C

[DavidBrough]

Well I suppose our typical Bank Holiday weather has a lot to answer for as I took the opportunity to spend three days in the garage and swap over my axles. I did the job on my own and everything was quite straight forward once you put your mind to it. I’ve only had chance for a quick spin round the block at this stage to check for any funny noises and make sure nothing fell off but it doesn’t half feel good, much quieter and no discernable difference when pulling away, I will have to test hill starts though. Will let you know how I get on when I’ve had chance for a proper drive. I now have a good 3.92 axle going cheap if anyone needs one.

David Brough
280SL Auto with A/C & 3.46 axle

[DavidBrough]

Unfortunately I seem to have an issue with my new axle as whilst it runs very well it is pushing oil out of the breather on top of the diff. When returning from a fast run I noticed some drips of oil on the floor and there was a clear line of oil down the back of the diff and the top of the breather had clearly visible oil all over it, there were no apparent leaks from anywhere else. I have removed and plugged the large breather pipe as others have done and the oil level is correct being just below the level plug hole. Could this be something to do with the removal of the large breather link pipe or may there be some other issue. At this stage I can only think of having a section of the rear chassis re shaped and refitting the link pipe to relive what appears to be a build up of pressure in the diff. I have removed and checked the small breather which is clearly the culprit and the felt pad is in place and I have applied sealer to the threads but to no avail.

Does anyone have any ideas or suggestions.


David Brough
1969 280SL Auto with A/C & 3.46 axle

[Naj ✝︎]

David,

 

quote:...the oil level is correct being just below the level plug hole.

With the car level on the ground too?

I'm thinking you may have too much oil in there...

naj

[DavidBrough]

Hi Naj,

That was my first thought but I have checked it several times on the level and no oil comes out with the level bolt removed. Do you know if it's possible for excess oil to remain in the axle tubes even when on the flat?

David Brough
1969 280SL Auto with A/C & 3.46 Axle

[paulr]

David,

I had this same issue with mine and even found a little oil on the rear under the bumpers but it has now settled down and having had it checked at Roger Edwards, it's all fine .Along with my 123 ignition it's the best thing I have done to the car. I hope you don't worry too much and enjoy it.

p.

[DavidBrough]

Hi Paul,

Do you have the link breatehr pipe in place as I know the boys at Roger Edwards do advocate this? This axle ratio is terrific though it turns the SL into the car I always wanted it to be.

David Brough
1969 280SL Auto with A/C & 3.46 Axle

[Naj ✝︎]

Hi, David,

quote:Originally posted by DavidBrough

Hi Naj,

That was my first thought but I have checked it several times on the level and no oil comes out with the level bolt removed. Do you know if it's possible for excess oil to remain in the axle tubes even when on the flat?

David Brough
1969 280SL Auto with A/C & 3.46 Axle

I think it was A Dalton who suggested that the level of oil shud be just below the filler plug' so you can 'feel' it with your 'pinky'!!

Were you able to get the correct oil for the LSD?

naj

[DavidBrough]

Hi Naj,

Mine’s just the standard one, no fancy LSD tricks like yours I’m afraid. I did use Arthur's “pinky” trick to check the oil level by the way and used straight EP 90.


David Brough
1969 280SL Auto with A/C & 3.46 Axle

[paulr]

blimey, I have no idea. They have carte blanche to do what is necessary, so only they know. Why not phone them and ask. Paul does my car and he is very helpful.

p

quote:Originally posted by DavidBrough

Hi Paul,

Do you have the link breatehr pipe in place as I know the boys at Roger Edwards do advocate this? This axle ratio is terrific though it turns the SL into the car I always wanted it to be.

David Brough
1969 280SL Auto with A/C & 3.46 Axle

[DavidBrough]

Hi Paul,

As Roger Edwards did yours you will have the breather in place as I know they always cut out a portion of the left hand chassis so it will fit and that’s what I’m thinking of having done in an effort to relieve what seems to be extra diff case pressure. However, there are a lot of people who have fitted the 3.27 axle which is similar and just removed the link pipe and plugged the holes.


David Brough
1969 280Sl Auto with A/C & 3.46 Axle

[jeffc280sl]

My 3,27 rear axle has plugs in place of the cooling tube ends.  There is no gear oil leaking from the breather outlet.  Is your breather located in the same place?

Download Attachment: 327 breather.JPG
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[DavidBrough]

Hi Jeff,

Yes, mine's in the same place as yours and I'm at a bit of loss to understand why the axle should show signs oil being forced out of it when the level's correct.


David Brough
1969 280SL Auto with A/C * 3.46 Axle

[Naj ✝︎]

Hi, David,

quote:Originally posted by paulr

blimey, I have no idea. They have carte blanche to do what is necessary, so only they know. Why not phone them and ask. Paul does my car and he is very helpful.

p

quote:Originally posted by DavidBrough

Hi Paul,

Do you have the link breatehr pipe in place as I know the boys at Roger Edwards do advocate this? This axle ratio is terrific though it turns the SL into the car I always wanted it to be.

David Brough
1969 280SL Auto with A/C & 3.46 Axle

Paul has a 3.69 which uses the normal (smaller) Pagoda type casing.
No cooling tube fitted.

Jeff's comment is interesting:
Where is the breather?

naj

naj

[jeffc280sl]

The breather is circled in red.  

Download Attachment: 327 breather.JPG
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I can't understand why it is leaking.  I'm sure the spinning gears kick up a lot of oil and splash it all around inside the diff case.  The gear oil is not otherwise under any pressure so as to defy gravity.  It must be the felt is too thin and what oil force is created by the spinning gears is sufficient to soak it through.