Is a W123 300D automatic directly compatible with a W126 300SD? - PeachParts Mercedes-Benz Forum

Zacharias · #1 03-16-2013, 12:02 PM

Quote:

Originally Posted by Stretch

I think I'm correct in saying that the "swap the tail ends" myth has been busted by the likes of mach4, rollguy and deliveryvalve.

x2.

I was about to get a trans from another member to go 126 -> 123 and decided to run it by my local indy Mercedes shop first.

The owner showed me the exploded parts diagrams for both. No way in hades I can see it working, from difference in the shape/footprint of the tail shaft housings alone. I was looking at the swap for a 1980 300td.

vstech · #2 03-16-2013, 10:33 PM

Quote:

Originally Posted by Stretch

I think I'm correct in saying that the "swap the tail ends" myth has been busted by the likes of mach4, rollguy and deliveryvalve.

Have a look for mach4's diesel SL (107) conversion thread - I think there's evidence somewhere in that mega thread.

nope, not TOTALLY busted... a 123turbo auto trans will work in a 126 if the tail shaft and sender ring is swapped. however, it will NOT work the other way around.

this is assuming both trans are the 722.3xx the 2xx and 4xx will not fit parts to the 3xx or each other.

the 123 mechanical sender fits on the 126 output shaft, but there is no provisions for oiling the parts... so only the electronic sender can be swapped...

Quote:

Originally Posted by Zacharias

x2.

I was about to get a trans from another member to go 126 -> 123 and decided to run it by my local indy Mercedes shop first.

The owner showed me the exploded parts diagrams for both. No way in hades I can see it working, from difference in the shape/footprint of the tail shaft housings alone. I was looking at the swap for a 1980 300td.

your 1980 722.2xx trans is totally different from the .3xx in the 126's...

Stretch · #3 03-17-2013, 03:04 AM

Quote:

Originally Posted by vstech

nope, not TOTALLY busted... a 123turbo auto trans will work in a 126 if the tail shaft and sender ring is swapped. however, it will NOT work the other way around.

this is assuming both trans are the 722.3xx the 2xx and 4xx will not fit parts to the 3xx or each other.

the 123 mechanical sender fits on the 126 output shaft, but there is no provisions for oiling the parts... so only the electronic sender can be swapped...

So in the context of this thread you are saying yes then?

You could use a 722.315 - remove the tail cone and the mechanical speedometer part and put the tail cone part from the 722.303 in its place.

mach4 · #4 03-17-2013, 10:23 AM

Quote:

Originally Posted by Stretch

So in the context of this thread you are saying yes then?

You could use a 722.315 - remove the tail cone and the mechanical speedometer part and put the tail cone part from the 722.303 in its place.

That's exactly what I've done on my 617->107 swap, although I used the tail cone from the 722.3 out of the 380SL. I also swapped the yoke in order to keep the SL's larger flex disks and driveshaft. It works perfectly.

Stretch · #5 03-18-2013, 04:16 AM

Quote:

Originally Posted by mach4

That's exactly what I've done on my 617->107 swap, although I used the tail cone from the 722.3 out of the 380SL. I also swapped the yoke in order to keep the SL's larger flex disks and driveshaft. It works perfectly.

Well it looks like I'll have to read through that thread again!

Confused - that's me...

mach4 · #6 03-18-2013, 10:29 AM

Quote:

Originally Posted by Stretch

Well it looks like I'll have to read through that thread again!

Confused - that's me...

I went back and checked the various threads and i don't think I ever detailed that part. When I replaced the 722.4 with a 722.3 I took the tail cone from the SL's 722.3 and swapped it to the 722.3 of the 300D. This is what gave me the electric speedo and the option to keep the larger yoke.

I considered this fixing a problem not part of the swap. Guess I should have documented it in the thread.

Stretch · #7 03-18-2013, 02:53 PM

Quote:

Originally Posted by mach4

I went back and checked the various threads and i don't think I ever detailed that part. When I replaced the 722.4 with a 722.3 I took the tail cone from the SL's 722.3 and swapped it to the 722.3 of the 300D. This is what gave me the electric speedo and the option to keep the larger yoke.

I considered this fixing a problem not part of the swap. Guess I should have documented it in the thread.

Hey that's fine - at least I'm not loosing my marbles faster than I thought I was!

Zacharias · #8 03-18-2013, 12:44 PM

Quote:

Originally Posted by vstech

your 1980 722.2xx trans is totally different from the .3xx in the 126's...

Do you mean the Bowden setup or something else? I was doing a complete linkage swap to use the Bowden setup on the earlier car.

Actually my '80 has a vacuum-control-only trans -- .117>? if I recall correctly.

When I saw the parts diagrams it was apparent how completely different the shape of the housing is in the tailshaft area. I could see a difference by looking at the pic of the trans I was supposed to get, but for some reason I still thought the other tailshaft housing would bolt up....