3.46 Rear Axle Rebuild

[DavidBrough]

Hi Jeff,

I did dismantle the breather and replace the felt pad and my replacement was a little smaller so the first time it leaked I took it apart and put the original one back but no joy. I don’t think the breather had been dismantled before so I think the pad is original.


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

[jeffc280sl]

I remember taking mine apart also.  Just can't recall the specifics internal to the breather.  We know this is where the leak is comming from so I would try different size felt filters to stop the flow while permitting some air in or out as required.

[DavidBrough]

Oil leak update.

After much messing around with the breather I seem to have failed in my attempts to stop or even stem the leak so I decided to have a flexible pipe made up to replace the old cooling tube. This seemed like a good idea at the time but there was still insufficient room and I couldn’t entirely keep it away from the chassis or prop shaft, however, whilst it was briefly fitted the axle didn’t leak. As a result I decided to talk to the UK Pagoda Gurus Roger Edwards Motors who said that they had fitted quite few 3.46 axles and had found that some leaked and some didn’t with no apparent reason as to why. Their initial fix was to extend the breather on the back of the diff into the boot/trunk with a brake hose and a small catch tank to collect any oil and allow it drain back. Whilst this seemed to fix the problem they had decided that the best solution was to always leave the cooling pipe in place by modifying the chassis slightly. My car is now booked in for the chassis mod and I will let you know how I get on with it.


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

[Naj ✝︎]

Hello, David,

Having to mess around with the structure of the car seems to me to be too drastic a measure....

I wonder if its worth trying a different brand or spec of oil (after flushing)? I think your current oil may be foaming too much?

I just took some pictures of the diff casing. There is plenty of room in there and the crown wheel is turning CCW but the breather outlet is facing away from the oil spray...



naj

[DavidBrough]

Hi Naj,

I know what you mean but I don’t think the mod is that drastic as only a small corner of the rear left side needs to be relieved a little to allow suspension movement and Roger Edwards Motors seem to think that should cure it.

David Brough
1969 280SL Auto with A/C & 3.46 Axle (still leaking)

[Naj ✝︎]

quote:Originally posted by DavidBrough

Hi Naj,

I know what you mean but I don’t think the mod is that drastic as only a small corner of the rear left side needs to be relieved a little to allow suspension movement and Roger Edwards Motors seem to think that should cure it.

David Brough
1969 280SL Auto with A/C & 3.46 Axle (still leaking)

OK.

Can you do 'before' and 'after' pictures please?

naj

[DavidBrough]

Here’s a few before photo’s, the area in question is the inside of the left hand chassis rail just after it curves forward, the square section of the corner needs to have a slight angle  to allow travel of the cooling pipe during suspension movement, it will actually fit whilst static but catches during suspension movement.


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


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[DavidBrough]

Success, axle oil leak now cured after fitting the large breather/cooling tube, pictures of chassis modification attached. Quite why it should leak in the first place is still a mystery but at least it’s cured now.


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



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[JamesL]

So trawling this thread, and the SLS site, would I be right in saying that:

 

• a 3.69 is an internal gear change  
• a 3.46 requires a bigger casing and therefore some mods under the car?  
• essentially, the difference will be about 250 rpm for the same mph?

Thanks

[DavidBrough]

Hi Tosh,

Yes, that’s about it. However, an internal gear change is a whole lot harder than an axle change and I would say you’re much better off swapping axles either way.

I thought about getting a 3.69 but decided that if I was going to do all that work I may as well go for the 3.46 on the basis that the 3.69 is much better than the 3.92 and the 3.46 is the same again on  the 3.69.


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

[Garry]

Hi David,

I have been reading with interest the change over of youraxle.  Whilst I am waiting to find a ZF 5 speed to replace my 4 speed and match my data card, which will probably take me years, I wouldnt mind changing over the rear axle.  Is it only the early 70's 280SE 3.5 that had a suitable 3.46 axle or are there other models that could do the job?

 Whilst I really would like to use a 3.27, that model was never sold in Oz (and I suspect the cost of shipping one from USA does not make it worth while) and the 3.46 appears to be the alternative I guess.

Thanks
Garry

[DavidBrough]

Hi Garry,

I’m fairly sure you will have to look for a 108 or 109 body 280 V8, not a 300 which had air suspension. I think Joe JA17 has posted a comprehensive list at some stage. You might want to try a search and see. I would highly recommend the change which isn’t that difficult to do once you put your mind to it.


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

[Garry]

Hi David,
Thanks for info.
I have located a  3.46:1 from a  280SE 3.5. and think I will go down this path at this point whilst waiting waiting for a ZF gear box to become available.

 Can I asume that the 280SE 3.5 is the one that will have the different brake caliper sizes that you discussed with Joe .  Did you have to change them over?
I am going to give a local mechanic that has done some of the work on my car, the whole screed that you wrote on the rear axle rebuild and see if he is happy fitting it and also doing the minor body mod.

Any further comment I should tell/ask him?
Thanks
Garry

[DavidBrough]

Hi Garry,

The difference in brake calipers is purely internal and any issue should only arise if you need to replace any of the parts. In that case you will just need to order 108 parts not 113. I assume the larger pistons give greater braking pressure. In my case the 108 calipers were scrap so I just used my existing ones.

The only real issue to consider is whether to go for the chassis modification and fit the cooling tube from the off as this is certainly much easier to do with the axle out. Many others who have fitted this type of axle found no problem with removing the cooling tube and the advice I had was that some seem OK without it and some don’t. Unfortunately you won’t know until the axles fitted and running although it is still possible to do this afterwards, as I did, but you will need to find a confident Pagoda mechanic.

Good luck, it’s certainly a change well worth doing.


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

[Garry]

Thanks David,

Am seeing the mechanic tomorrow.
I note on some of the 3.27 mods that they put a plug in the breather tube outlet.  Is the breather tube critical in a 6 cylinder car vs the V8 thus if finding that it doesnt fit, you could then plug it?

Garry

[DavidBrough]

Only if you have one of the axles that leak without it.

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

[JamesL]

Yeehah!

Have found a good 3.46 limited slip diff from a W108 220SE. I know, wrong car. The guy I am buying it from sold the original axle to a customer with a broken Pagoda axle. Found a w108 for parts, re-furbed the axle and put it under his 220. And now I have bought it as he will swap my axle into his 220.

Anyhoo... once I have it, do I need to recalibrate the speedo?

[waqas]

quote:Originally posted by Tosh

Anyhoo... once I have it, do I need to recalibrate the speedo?

Yes, I believe so.  Good time to have it serviced (lubricated, etc).

[Garry]

Hi James,

My 3.46 now fitted is fantastic and really makes the driving much better especally first and top, then again mine is a 4 speed manual. I have fitted 215.60.14 tyres and I am finding that at 52mph reading on speedo I am doing 100kph or 62mph actual and the revs are running around 2750.

I have noticed on the floor of the garage that there are a couple of drops of oil but I have not had time to get it up on a hoist yet to see if I can fix that.

Good luck with fitting it.  ps Try to avoid replacing the brake cables they are very expensive. I had to get some in from Germany and got stung AUD$700.

[DavidBrough]

Hi Garry,

That price for the brake cables sounds very excessive as SLS list them at Euro 40 each. When I fitted mine I had a devil of a job removing the cables from my new and old axle as they were completely rusted in but decided to persevere and eventually got them out with lots of heat, I even melted the cable on one. Thankfully I managed to get two good ones from the four. If you have to order new ones be careful as the ends differ where they meet the actuating lever at the wheel hub, if in doubt get the actuators to match the cable at the time as they are only Euro 6 each



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