2.47 Diff from Gen II w126 to Gen I: can it work?

[WDBCB20]

I'm getting conflicting reports on this e.g.:

"To clarify, I did the swap 84 300SD (W126) from a 87 420SEL. The SD has the wider differential so it required the axle half-shafts as well. It also required swapping the yoke from the SD."

vs

"Note that Generation II is not at all the same and the 2.47 uses the larger carrier.
Be very careful regarding Gen I versus Gen II. They do not exchange."

So which is it?!?

[vstech]

The gen 2 can be used ... if you swap the subframe.

[Frank Reiner]

Apples: The width of the center sections, also known as differentials.

The '84 SD originally had a 185mm ring gear diff, which is a narrow one.
After installing the 210mm ring gear diff from the '87 SEL, the '84 then had the wider one.

Originally Posted by WDBCB20

I'm getting conflicting reports on this e.g.:

"To clarify, I did the swap 84 300SD (W126) from a 87 420SEL. The SD has the wider differential so it required the axle half-shafts as well. It also required swapping the yoke from the SD."

Oranges: The mounting of the center sections, irrespective of width, was changed for the Gen II. As noted by vstech.

"Note that Generation II is not at all the same and the 2.47 uses the larger carrier.
Be very careful regarding Gen I versus Gen II. They do not exchange."

So which is it?!?

Originally Posted by vstech

The gen 2 can be used ... if you swap the subframe.

[WDBCB20]

Originally Posted by Frank Reiner

Apples: The width of the center sections, also known as differentials.

The '84 SD originally had a 185mm ring gear diff, which is a narrow one.
After installing the 210mm ring gear diff from the '87 SEL, the '84 then had the wider one.





Oranges: The mounting of the center sections, irrespective of width, was changed for the Gen II. As noted by vstech.

Clearly my understanding of this remains woefully unsophisticated.

So what is it that the Gen II subframe has that the Gen I does not? In other words, why won't the Gen II (Just the axles and diff.) assembly work with a Gen I car?

This quote: "To clarify, I did the swap 84 300SD (W126) from a 87 420SEL. The SD has the wider differential so it required the axle half-shafts as well. It also required swapping the yoke from the SD." I got from a post by "SD Blue" found here:
2.47 diff in a w123?

Would it not seem to suggest only "the axle half-shafts and swapping the yoke from the SD" (not swapping the subframe - a hellish job involving taking off the shocks and springs) were required to make it work?

[Frank Reiner]

Originally Posted by WDBCB20

So what is it that the Gen II subframe has that the Gen I does not? In other words, why won't the Gen II (Just the axles and diff.) assembly work with a Gen I car?

The mounting points for the center section (diff) on the sub-frame were revised on the Gen II sub-frame to incorporate rubber isolators that were not present on the Gen I design. As a consequence, the castings of both the main case and the cover were also revised to match the sub-frame revisions and isolators.

[WDBCB20]

Thanks,

Can't get any clearer than that.

And would also appear to bring into question the veracity of "SD Blue's" claim of having swapped an 87 420SEL diff into an 84 SD with no mention of a subframe swap.

[Clemson88]

One of the reasons I kept the 85 gas diff was because it had a wire running to the ABS system. I kinda wanted to keep the gear anyway but didn't know how not having that sensor would make the ABS behave. Someone might share that with me if anyone knows.

[pawoSD]

We swapped the 2.47 from a 1984ish 500SEL I believe when we installed it in the 1983 300SD. It worked but wasn't that great...made the car slow and 4th gear worthless under 55mph. 2.88 is the best ratio for the 617 powered cars unless all you do is cruise @75-80mph all day on the freeway, then the 2.47 gets you less noise/rpms, but not really any fuel savings.

[greazzer]

Originally Posted by pawoSD

We swapped the 2.47 from a 1984ish 500SEL I believe when we installed it in the 1983 300SD. It worked but wasn't that great...made the car slow and 4th gear worthless under 55mph. 2.88 is the best ratio for the 617 powered cars unless all you do is cruise @75-80mph all day on the freeway, then the 2.47 gets you less noise/rpms, but not really any fuel savings.

That's really not accurate. I have a 2:65 LSD and it ran great with a 617 NA (617.912). Getting ready to try it out with the turbo flavor 617.952.

I have a 2:47 and I am thinking of popping it in to see for myself how it behaves. Lots of experts said the 2:65 would never work out well and that was simply not accurate.

[SD Blue]

IIRC, the differential and axles were from separate vehicles.
Differential 2:47 GEN 1 (420/500SE?)
Axles GEN II (420SEL) 87?
The GEN I and GEN II have a different rear mount and subframe.
I apologize if this caused misinformation or confusion. That was a few years ago and the hazards of old age and hospital stays have clouded the memory.

Here is a link to what I used to sort out what is workable:
Mercedes Benz EPC Type W126 126 Information Everything Benz

Yes, the 2:47 is a little slow off the line but I'm not interested in red light-to-red light racing so it works fine for me. I've never had any trouble with an on-ramp.

[Clemson88]

Originally Posted by pawoSD

We swapped the 2.47 from a 1984ish 500SEL I believe when we installed it in the 1983 300SD. It worked but wasn't that great...made the car slow and 4th gear worthless under 55mph. 2.88 is the best ratio for the 617 powered cars unless all you do is cruise @75-80mph all day on the freeway, then the 2.47 gets you less noise/rpms, but not really any fuel savings.

It's done. The engine and transmission are in the body along with the diff yoke and drive shaft assembly and they aren't coming out unless they breakdown or wear out.

I care little about acceleration or fuel mileage. I don't go much and when I do I have plenty of time to get there and get back. If I hit the highway I expect to drive fast so I will spend less time on the road and more time recreating.

[tjts1]

With a 2.47 you're just a rolling road block.

[WDBCB20]

Originally Posted by SD Blue

IIRC, the differential and axles were from separate vehicles.
Differential 2:47 GEN 1 (420/500SE?)
Axles GEN II (420SEL) 87?
The GEN I and GEN II have a different rear mount and subframe.
I apologize if this caused misinformation or confusion. That was a few years ago and the hazards of old age and hospital stays have clouded the memory.

Here is a link to what I used to sort out what is workable:
Mercedes Benz EPC Type W126 126 Information Everything Benz

Yes, the 2:47 is a little slow off the line but I'm not interested in red light-to-red light racing so it works fine for me. I've never had any trouble with an on-ramp.

Thanks for the kind correction and link. Another illustration of the power of this website where sharing varying experiences and insights can lead to more accurate understanding..... or not, lol.

What I'm really curious about - does the kickdown still give you the same boost allowing you to pass quickly at highway speeds or is that also negatively affected? If not, can that be remedied by shifting to third manually?

[WDBCB20]

Originally Posted by pawoSD

We swapped the 2.47 from a 1984ish 500SEL I believe when we installed it in the 1983 300SD. It worked but wasn't that great...made the car slow and 4th gear worthless under 55mph. 2.88 is the best ratio for the 617 powered cars unless all you do is cruise @75-80mph all day on the freeway, then the 2.47 gets you less noise/rpms, but not really any fuel savings.

That 3000 rpm howl you get with the 2.88 when you're barely pushing a little over 70mph is just not acceptable anymore when cars nowadays gets you that speed at most at 2700 rpm if not much lower.

[okyoureabeast]

Originally Posted by WDBCB20

That 3000 rpm howl you get with the 2.88 when you're barely pushing a little over 70mph is just not acceptable anymore when cars nowadays gets you that speed at most at 2700 rpm if not much lower.

I think you should be looking at transmission rather than differential upgrades if lowering cruising rpm is your goal.