Year flexibility
 

Okay after months of working like no tomorrow I decided to revive my car, I found an eng/trans from a newer (1986 300SD) so I am told. What are the year flexibility to swap over the engine and trans, since I have a 1985 how old and new can I go and still be able to swap things over without any major modification or fabricating. I was thinking like so, 82, 83, 84, (my car 1985) 86, 87, 88 and so on. Thanks in advance.

The short (and probably incomplete) answer: '81 to '85 were essentially the same car. The '86 to '91 version was a fairly substantial update. While I'm sure it's possible to transplant a late drivetrain into an early 126, I'm going to make a semi educated guess that there's considerably more work involved than keeping with the '81 to '85 donor cars.

There is no '86 300SD. The 5 cylinder 300SD was offered from '81-'85 followed by the 6 cylinder 300SDL in '86 and '87 then the 6 cylinder 350 SDL in '90 and '91 and the 350SD in '91. If you have both cars, an engine swap won't be that difficult.

Sixto
87 300D

Did they not go to an aluminum head in 86? Inferior product.

6 cylinder Diesels from '86 have aluminum heads.

Sixto
87 300D

Answer
 

The 1985 transmission is unique better gear ratio = don't change it.

The engine range is:
* 300SD 1978-1985
* Any W123 chassis Turbo OM617.952 1981-1985 will work.



.