230 SL - lower ratio pinion 3.69 - easy swap?

[Erik]

Hello,

I have a 1966 230SL automatic.
It has its original rear axle with drum brakes and the 4,08 ratio.

I would like to keep the drum brakes but reduce the ratio to 3.69 or even 3.46 for lower fuel consumption.
The best option seems to be to remove the original drive gear and pinion and replace them by new parts with the lower ratio.

So I removed the pinion last week (I was unpleasantly surprised by the complexity of that axle) and I am about to order the lower ratio drive gear, pinion and bearings.

However, according to the SLS catalogue the 3.69 nor the 3.46 were available to the 230SL. The 3.69 is a 250/280SL thing and the 3.46 a 300SEL saloon equipment.

Could anyone confirm me whether the 4.08 and 3.69/3.46 parts are interchangeable? Do I need to do some modifications to make them fit in the 230 axle?
What are the parts-numbers I need to order?

PS: I asked some MB dealers but they are no help at all. Their knowledge is limited to 21th century cars.

Thank you for any advise on that subject.

Thank you,
Erik

[Garry]

Hi Erik,

There has been lots and lots of discussions and that question asked on many occasions and the simple answer is no, the crown wheel and pinion does not fit in the w113 axle pumpkin and you need to do a complete axle swap from the sedan to achieve the conversion.

Been down that road myself some years ago.

Garry

[DaveB]

I believe the 3,75 is the only option.

[Benz Dr.]

I believe the 3,75 is the only option.

Dave is right on this one. The 3.75 is the standard gear ratio for 230SL's and that's the axle I'd use. Even with this axle ratio performance is affected somewhat and accceleration in high gear suffers a bit. I wouldn't go to the 3.46 in anything less than a 250 and a 280 would be preferable.
If I lived in the mountains or very hilly country, I'd want a 4.08 in a 230SL, escpecialy if it was an auto trans.

[ja17]

Hello,

There are two or three different size rear differential castings for the MB cars of the era. I believe that the 6.90 ratio was produced in both the large diameter and small diameter configurations. The smaller gear sets were special order for a 250SL, 280SL. It was also used in 300SE,SELs (six cylinder cars). These gear sets should fit fine.  The 6.90 gear sets out of the V-8 sedans were the larger diameter sets and they will not fit in your original rear diff.

[Garry]

Dan and Joe,

After all these years of people saying that you cannot lower the ration by just changing the crown wheel and pinion you are saying that it can be done?

So on that basis I can I now just change the crown wheel and pinion from my car that currently has a 3.46 out of the V8 and convert it back to the 4.08 that I still have from the conversion some  years ago with out changing the whole axle now that I have the 5 speed gearbox in??

[114015]

Rear Axles,

Dan, Dave and Joe are right.

There are basically two different axles for the W113:
230ies had the W110/111 fintail rear axles with small differential housing and drum brakes,
250/280ies came with the W108 rear axles with larger differential housing and disk brakes.

You can only change pinion and crown wheel within your type of axle - i.e. between W108 ans 250/280SL OR W110/111 and 230 SL.

The 3.46 wheel set came out of the 3.5 (and 4.5) litre cars and (should) fit the W108/109 housings and also of the 250/280 SL. Some adaptation necessary here (cooling tube, etc.)

For the 230 you can only use the original 4.08 or the 3.75 wheel set that was in the 230 SL (non US) only
(don't know about the W112 300 SE 3.75 option...).

So Erik, if you want to keep your matching-numbers-drum-brake rear axle go and get a new A113 350 01 39 wheel set for € 900 (or a little more) and be happy.
Lower rear end ratios are only possible with the W108/109 differential housing.

If I were you (well, I am not but we both share at least the same red color) I would go with Dan's advice.

Good luck

Achim
(with conversion from 4.08 to 3.75)

[Naj ✝︎]

Hello, Achim,

The diameter of the 3.46 and 3.27 crown wheels is too big to fit into a 250/280 axle casing.

There is a company in Germany that do it but the casing(s) need to be machined out.

Anybody here have instructions on how to set the back-lash on these crown wheels/pinions?

Naj

[Garry]

Thank you Naj,

I have been sitting here all morning cursing that I went through the whole exercise of replacing my entire rear end and brake cables in the 280SL and then seeing these postings that had appeared to support the theory that you can fit the crown wheel of the 3.46 into the existing W113 pumpkin. 

With My 230SL I was not going to bother due to cost of the whole lot.  However if I can get the gear set that does fit into the 230 and it indeed fits then that is a bit different.

[ja17]

Switching ring and pinion gear sets is a very complex and exacting process.  Even experienced techs avoid this project. Be sure to read all the information in the BBB before you decide to undertake the project. In addition the gears sets are expensive and some ratios are NLA.

I believe that the 6.90 is one of the ratios which was produced in both the large and small gear sizes.

[George Des]

I'll second what Joe says about tinkering with the ring and pinion gear in the rear differential. I rebuilt a spare 230sl 3.75 ratio rear end about three years ago. I completely disassembled it to change out all the bearings, seal, crush sleeve etc. It is a big job just to just get it all disassembled. Then there is the issue of setting the backlash. Some of the manuals include info on how to ensure the mesh of the gears is correct using red rouge or even lipstick, but this is for the most part a very tedious and trial and error process accomplished by fitting shims of various thickness to the left side axle tube. This is especially the critical if you are fitting a brand new set of ring and pinion gears. When I did my rebuild, I used the same ring and pinion and replaced all shims exactly the way I found them. Based on some on line discussions with Jim Villers, I feel as though I got the backlash reasonably close to what it was before i disassembled everything, but there is still some lingering doubt because it is not all that easy to check--I guess the real proof will be when I one day install this rear end and get to listen to whether it whines or not!

George Desiderio

[stickandrudderman]

I rebuilt a diff when I was an apprentice 30 years ago. I haven't bothered trying to repeat the excercise since.

[66andBlue]

  Hmmm ..
You mean you haven't bothered doing it again because it is so easy that you were successful the first time?   
Or because you could not stand the whining of the rebuilt?   

[GGR]

I drove a 230 once and it's a happy revving engine. As Dan said, a lower rear end gear ratio may result in a car that will be less pleasant to drive as spacing between gears will be too big. Have you considered a 5 speed conversion? The Getrag 265 conversion is well documented and there is an adaptation kit readily available. The 0.81 fifth will lower your rev by 20% on the highway.

[Cees Klumper]

Plus, the post originator says he want to change the ratio to improve mileage. I did it to lower RPM's on the highway, not to lower consumption and I would not have gone through the project if fuel consumption had been my main concern. I don't think it makes that much difference, everything taken together.