Turbo Swap into '78 300D
 

I have a 1978 300D with only 153k miles and the body/interior is in fantastic shape.
Unfortunately the motor is bad (guzzling oil, lots of blowby) and I'm not so sure about the transmission either.

The only good motor I have is a CA turbo motor from a 1985 300SD.
I have another bad turbo motor (crack in the crankcase) and I'm planning on swapping over the air parts from that one onto the 85 so I don't have the trap oxidizer and such.

I'm planning on swapping in a good low miles transmission from an 83 300CD and a 3.07 rear end to replace the 3.46. Also need to swap in the exhaust.

Are there any other complications with doing this swap? Anything else I should be prepared for?
I know the speedometer will be off, I might replace that too.

Throttle linkages will be a challange

They won't swap directly from a turbo W123 coupe/sedan?

I don't think so, the early w123 linkage goes under the exhaust manifolds and over the valve cover....the w123 from the 80s there is a throttle pivot busing on the firewall that runs the linkage right near the IP and valve cover....not positive but you may be able to get the linkage you need from a w116 300sd...

Just swap over the firewall bracket from a later model donor car like I did. You can drill out the spot welds to remove it, and either weld it on the recipient car like I did, or attach it mechanically with rivets, screws, etc..

Many details in this swap.

- Another reason you have to swap the entire linkage setup from the turbodiesel donor car as the trans in the later car has its shift points controlled by a Bowden cable, which the '78 doesn't have.

- The turbo has a radiator with no cap, and an overflow tank. The NA has a rad with the cap on top.

- Unless you choose to delete it, the overboost protection switch.

- The oil filter canister assembly will have to be changed to a w123 one. The w126 one is different and won't fit.

- Ditto for the 'horns' (brackets) from the block to the engine mounts.

- The '78 is wired for the old series glow setup. Unless it happens to have an updated glow system installed, you will have to investigate how to integrate the later style preglow relay (under the hood) into the harness from the keyswitch, or simply install a manual controlled preglow relay using a pushbutton or momentary switch.

Good news is that splicing a later model glow system in to the earlier car is pretty straight forward, as is adding the turbo radiator overflow tank. (Personal experience speaking on both counts.) Feel free to ask me about it if you need to.

are you sure you're not sucking oil into the engine via a bad vacuum pump diaphragm? 153k is low miles for those kinds of problems.

there is a different sized pilot bearing in the CA 85 engines, or at least i've heard so. the mechanic who did my swap had to have some machining done to fit it all together.

Your early chassis will have the engine dampers (shocks) in a different spot, and you may only be able to use one side (Driver side I think). Other than fabbing a mount, just having only one may be your only option. On my '81 300D, I think I just left them both off (don't exactly remember), and it has not been a problem.

I agree! It may also be a bad lift pump, there has been issues with the pump going bad and oil getting sucked into the fuel...

I may be wrong, but I think the 126 oil filter stand is just a little further forward (great for a 617 in a 107 chassis like the one mach4 did), so it should not be a problem in a 123. However, it would be a problem the other way around (123 stand in a 126), as it would hit the PS box.

That may well be. I am repeating what comes to mind from the laundry list of things to watch for that I got when I considered a w126 drivetrain for my early CD.... :eek:

Wow this is lots of great info, thanks everyone!

Just put a new diaphragm in it. Haven't checked the lift pump. The blowby is awful, however. Could that be caused by the oil getting sucked into the fuel?

I started rethinking the swap plan. What about staying with the 722.118 mechanical-modulated tranny and only swapping the diff? I have another good one from a 1980 300D with only 160k miles (I don't trust the tranny that's in there) Then I wouldn't have to mess with the linkage coming out of the firewall.
Is the gearing way different on a 1980 722.118 versus a 1983 722.3x?

Have you checked the blowby since you put in a new diaphragm? Can you post a video of the blowby?