W108 engine & drivetrain transplant

[Dawie]

Hi Guys,

I am from South Africa and new to this forum and I hope to gather valuable information from all the experienced owners of these amazing cars!

I have recently acquired my first old Mercedes Benz. It is a 1968 W108 280SE body that the previous owner fitted with a 1982 380SE V8 engine and auto transmission. The original differential is still in the car and the final drive ratio needs to be changed. The original diff's ratio is 3.92 - I think. I think that the final drive ratio of the 380SE M116 engine is 2.47 but I am not sure. So - obviously not a good match!

What would you advise me to do? Try to find a replacement diff? Which models would work? Or what other solutions?

Thanks in advance!

[JeffreyNMemphis]

You should send a message to a member who uses MercMad as his forum name. He has much experience with various engine and transmission swaps. He probably can tell you what options are compatible. Wish I could be more helpful.

Welcome to Peach Parts!

Upload some pictures of you car. We love pictures!

[Dawie]

Thanks, I have send a mail to MercMad63.

Will post some pictures soon.

[JeffreyNMemphis]

I like the idea of swapping in a V8 Mercedes engine. The last year of the W108 chassis had a 4.5 liter V8. My first MB was the 1973 280SE 4.5. It ran like a scalded cat. I wish you great success and look forward to pictures and video of your running project.

[Dawie]

I got a reply from MercMad63 and thought to share it.

First my e-mail to him:

I am from South Africa and new to this forum and have recently acquired my
first old Mercedes Benz. It is a 1968 W108 280SE body that the previous
owner fitted with a 1982 380SE V8 engine and auto transmission. The original
differential is still in the car and the final drive ratio needs to be
changed. The original diff's ratio is 3.92 - I think. I think that the final
drive ratio of the 380SE M116 engine is 2.47. So - obviously not a good
match!

I have been advised to try and find replacement axles from a W108 4.5 or a
W109 6.3 lt. But here in South Africa they are like hens teeth....

What would you advise me to do?
(a) Send the diff to an engineering outfit and have the final drive ratio
changed to 2.47? (Quite costly.)
(b) I suppose an axle / diff from a later model 380SE would not fit the W108
body?

Or what other solutions?

His reply:

Hi, I have done this xswap a few times . Yes you need to up the final drive.
Your other option is to buy a diff from a W108 280SE 3.5 whyich 3.25:1 and
bolts in or import the crown wheel and pinion from the USA for the 4.5.
If tyou want tyo save a bit of money swap in the whole rear end from a W126
(380SE) . you will need to weld in a brace for the diffs rear mount. Weld in
a bracket for the two front mounts and get the springs remade because the
originals are too soft and the W126 springs will not fit. It sounds like a
lot odf work but it's actually quite simple.

My questions:

@ MercMad63: Have you got some photos of the modifications of fitting the W126 axle on a W108 chassy?

@ Every one else: Do you know of a crown wheel and pinion for sale as suggested above? What other parts do I need to replace when changing the crown wheel and pinion in the W108 diff?

Thanks in advance!

[Frank Reiner]

Dawie:

As an alternate to the V8 W126 cars (2.47), the 4.5L V8 W116 cars were equipped with 3.07 rears, and are effectively the same swap as the W126.

We should note that some 5 and 6 cylinder cars in both W116 and W126 series were equipped with 3.07 (and possibly 2.88) rears, but although the ratio may be the same , the crown wheel diameters are different. V8s-215mm, 5&6 cyl.-185mm.

The 2.47 ratio can feel rather tall geared and sluggish for some tastes, but economical.

[Tony H]

I could not tell if it had been suggested to install a 3.27 axle from a 280SE 4.5-it should be plug and play with the exception of possibly removing the oil tube.

[Dawie]

I could not tell if it had been suggested to install a 3.27 axle from a 280SE 4.5-it should be plug and play with the exception of possibly removing the oil tube.

Yes, thanks also a possibility.

Considering the fact that I am in South Africa and the high shipping cost from the US, can I just get a crown wheel and pinion from W108 / W109 cars (4.5 or 6.3) and swap it with my original 280SE 2.8 crown wheel and pinion?

[Tomguy]

You can likely do this, but not likely yourself. Setting the proper specs in a gear can be difficult for even a good tech to get right, and is very tricky for someone even fairly advanced in terms of mechanics. Get it wrong and the gears will wear out very quickly!

[Dawie]

You can likely do this, but not likely yourself. Setting the proper specs in a gear can be difficult for even a good tech to get right, and is very tricky for someone even fairly advanced in terms of mechanics. Get it wrong and the gears will wear out very quickly!

I know of a very good engineering shop specialising in diffs that could probably do the job. I have also asked him if he could change my current diff's ratio and he said he could. The cost would be around ZAR5000 (USD430) he said. All this over the phone...

What can I expect to pay for a crown wheel and pinion in the US (if I can find one)? I just want to see if it would make sense trying to source it abroad.

[Tony H]

This thread might give you some insite to the process of changing R&P gears. It's doable if you have the correct tools, press and shims. I was ready to install a new locking differential on my Tacoma until I found it was only $120 if I removed and brought the diff in to the shop.
3,27 axle checkout, reseal, repair & install

[Dawie]

http://www.peachparts.com/shopforum/attachments/vintage-mercedes-forum/127054d1421937103-w108-engine-drivetrain-transplant-mercs.jpg
At last, here is a photo of my cars.

The blue one is a 1972 280SE with a lot of rust at the bottom of the doors and would probably be a donor car. The engine was overhauled in 1997 and is still OK. I do not know about the automatic gearbox though. It does not start in P (probably just a switch) and the car rolls when in P. Floorshift.

The black one is a 1968 280SE with the 1982 380SE engine and gearbox. Column shift. Have to change the final drive ratio in the diff.

[JeffreyNMemphis]

Nice picture!

The W108 automatic transmission does have a switch that won't allow you to start car in reverse or drive. I know I have read a thread on this forum on that subject.

Column shift versus floor shift seems more likely to be an issue of linkages rather than vastly different design and compatibility.

Thank you for sharing your project with us. I have faith that you will get this sorted out. I am subscribed and interested in your success.

Best regards,

Jeffrey