2.47 in 300SE

[Brian Carlton]

I've recently acquired a 1989 300SE in excellent condition with less than 100K miles.

Although the M103 is turbine smooth, it turns way too fast for my tastes..........coming from diesels exclusively.

Furthermore, for reasons that totally escape me, the vehicle utilizes only three gears in normal operation..........second, third and fourth.

I did a comparison on the final drive ratios currently with the 3.46 and potentially with the 2.47:


3.46:

12.73
8.34
4.98
3.46


2.47:

9.08
5.95
3.55
2.47


Looking at the numbers, the vehicle would have slightly shorter gearing utilizing 1,2,and 3 as compared to its current use of 2,3, and 4. This would improve it's launch and driveability in town.........which is currently quite good.

The magical 4th gear would give me the fuel economy on the highway that I desperately need.


All of the above is based upon the premise that I can modify the valve body to get permanent first gear start.

I'd like some opinions from those who have some experience with such a change........possibly from those with the W124 with taller diff gears.

[mbdoc]

Brian, have done several differential swaps like that.
The 2.47/1 is way to drastic for that car/

Have done several cars with 2.88/1 diffs & they are much better to drive than the 2.47/1 cars.

[Brian Carlton]

Originally Posted by mbdoc

Brian, have done several differential swaps like that.
The 2.47/1 is way to drastic for that car/

Have done several cars with 2.88/1 diffs & they are much better to drive than the 2.47/1 cars.

Pat, can you elaborate on the specifics?

The three lower gears will be shorter than the current set of three upper gears allowing it to drive better around town.

The final 2.47 might be too tall for the highway for climbing hills, but there should be no issue in using third for that purpose..........it's final drive is 3.55.........almost identical to the current 3.46.

If I use the 2.88, I can't really use third as a fallback position on the highway..........the final drive would be 4.14............very fast.

[S-Class Guru]

Brian, I've suffered for 20 years with the exact same issue. I seriously thought about a swap; but upon investigation of a viable 1st gear start modification, I came up a little confused. Some old posts herein said to just swap a spring in the valve body - but followup posts said that trashed the tranny in short order.
One old poster was said to modify the valve body for about $200, but I couldn't find him.
Another post talked about an electrical add-on that tricked the tranny into very quickly shifting down to 1st on startup. That seemed to invite potential rough shifting in my opinion. Then, I observed that when I manually placed the shifter in 1st, the 1-2 shift had a tendency to be pretty rough.

Looking at optional diffs, I concluded that the diff you mentioned would seem to be the correct one, but it might tend to downshift in a high headwind, who knows? Also, it seems there are various configurations of diffs, so I assumed I would get one that didn't fit, when I found the proper ratio.
So, I put it off, and now 20 years later I still have the car; but now it's relegated to in-town use only, so problem solved.

But, if I had it to do over, I would certainly pursue it more dilligently.
The engine has seemed to survived the high revs easily for over 200k miles, but I have gone thru a bunch of accessories like water pumps, fan bearings, etc; that might have lasted longer. And, 18 MPH on the highway is pretty tough these days.

Go for it!

DG

[sixto]

Brian, how about an SDL tranny and diff? Tighten the Bowden cable to hold gears longer.

124.032 tranny with 126 tail housing?

There's always a 722.5/6 swap

Sixto
87 300D

[Brian Carlton]

Sixto........

Here's the problem that I see with the 2.88:

If you attempt to use all four gears, 1-3 will be very short:

10.6
6.9
4.1

The current vehicle has ratios 2-4 of:

8.3
5.0
3.5


I do not believe that you want ratios that are that short around town. The current setup is relatively short and it shifts very quickly.

If you use the 2.88 and keep second gear start, the vehicle will be slow as hell on launch.

[Brian Carlton]

Originally Posted by S-Class Guru

Brian, I've suffered for 20 years with the exact same issue. I seriously thought about a swap; but upon investigation of a viable 1st gear start modification, I came up a little confused. Some old posts herein said to just swap a spring in the valve body - but followup posts said that trashed the tranny in short order.
One old poster was said to modify the valve body for about $200, but I couldn't find him.
Another post talked about an electrical add-on that tricked the tranny into very quickly shifting down to 1st on startup. That seemed to invite potential rough shifting in my opinion. Then, I observed that when I manually placed the shifter in 1st, the 1-2 shift had a tendency to be pretty rough.

Looking at optional diffs, I concluded that the diff you mentioned would seem to be the correct one, but it might tend to downshift in a high headwind, who knows? Also, it seems there are various configurations of diffs, so I assumed I would get one that didn't fit, when I found the proper ratio.
So, I put it off, and now 20 years later I still have the car; but now it's relegated to in-town use only, so problem solved.

But, if I had it to do over, I would certainly pursue it more dilligently.
The engine has seemed to survived the high revs easily for over 200k miles, but I have gone thru a bunch of accessories like water pumps, fan bearings, etc; that might have lasted longer. And, 18 MPH on the highway is pretty tough these days.

Go for it!

DG

Thanks DG.

Here's where I am with it:

The first gear start module that is used on the V8's won't work on the I-6

The valve body can be modified for first gear start, however, I, too have not confirmed if the posted spring relocation is correct or not.

There is a place in OK that should be able to accomplish it for a few hundred..........I'll investigate that.


With regard to the diff, as far as I am aware, the 2.47 from the V8's (second generation 126) is a direct exchange.

This one supposedly gets 21 on the highway and I'd like to increase it to 24 if I can.

[sixto]

Have you tried the brake pedal to kickdown switch bridge for kicks?

Sixto
87 300D

[Brian Carlton]

Originally Posted by sixto

Have you tried the brake pedal to kickdown switch bridge for kicks?

Sixto
87 300D

Please explain..............??

[JohnM.]

A complete FGS valve body from a 90-92 300E should be a direct swap.

[sixto]

Originally Posted by Brian Carlton

Please explain..............??

W124 First gear start and Transmisson question

But there's also this -

Auto Transmission secong gear start.

Sixto
87 300D

[compu_85]

Originally Posted by sixto

But there's also this -

Auto Transmission secong gear start.

That sounds like the best solution... the car rests in 2nd gear but moves off in 1st... the power you want but it "pulls" less when stopped.

Plus you could hook that system up to a switch so you could still move off in 2nd if you wanted to.

-J

[Brian Carlton]

Originally Posted by sixto

W124 First gear start and Transmisson question

But there's also this -

Auto Transmission secong gear start.

Sixto
87 300D

I've done some research and found those threads, but dismissed the electronic FGS due to the following post by Satish:

Factory FGS module? (002 545 41 32)


He doesn't explain why the kickdown switch won't work for six cylinder vehicles, but in another thread he refers to insufficient pressure at idle to achieve the 2-1 downshift.

[pawoSD]

M103 has nowhere near enough torque to handle a 2.47 diff in a W126. The 300E has a 3.07 and its about perfect. The use of only 2/3/4 is annoying, but it drives ok, and you can easily force a first gear takeoff if you want with the shifter.

A diesel can handle the 2.47 in a W126, we had that setup on our now retired parts car....its a little slow to accelerate but cruises at 75 great since it has better low end torque than a M103.

So far I've found the M116 to be a perfect fit to the W126 for all uses, and the 617 is optimal for 0-60mph driving and city driving....the gearing and torque makes it fly around town. (with a 3.07 and 2500rpm torque converter) The gassers are a bit slow on the getup and go in the city unless you shove excess fuel into them due to the 2nd gear start, more of an issue with M103 than M116.

[Brian Carlton]

Originally Posted by pawoSD

M103 has nowhere near enough torque to handle a 2.47 diff in a W126.

It would be beneficial for you to read and understand the final drive gearing for the existing vehicle and for the proposed vehicle before you draw a conclusion that is not based upon any engineering data.