The R/C107 models had an extremely long production run – 18 years. There were a variety of different models and specification changes. This included the differential ratios that can have a big impact on the performance and economy of the vehicle.
In compiling the table below, I have tried to research the various country specific variants. It is possible I have missed a few. Please indicate in the comments below if that is the case.
The SL and SLC of the year had the same mechanical specification (at least during the SLCs production run). The only exception was the 450SLC 5.0 where there was no equivalent 450SL 5.0 until the facelift and the 500SL model.
Many of the same aspects that were covered in the W126 table are applicable here. As with the W126, the V8 models received the larger (1.3l) case. Also, as with the W126 models, Mercedes-Benz went on a fuel efficiency drive during 1981 which is why the V8 cars got revised ratios. The project was called the “Energy Program” and included other changes such as the revised Bore/Stroke of the 380 engine.
Early in the first generation production, the 450 models moved from a 3.07 ratio to 3.06. This was achieved by changing from a 46:15 gear set to a 52:17 gear set. This was more of a minor specification change than any real impact on the car.
From the long term ownership of a 450SLC, I think the chosen ratio works well for that car. I’m not as sure of some of the other ratios. My view is that some of the later ratios were too tall. They probably worked a bit better for the home market on the Autobahn than in countries with lower speed limits.
The other factor to take into account is that this generation of Mercedes-Benz automatic transmission did not feature a lock-up torque converter. This means there will be some level of slip and engine revs will be slightly higher than the theoretical number.
| Model / Year | Differential Ratio | Speed at 1,000 RPM (4th) | RPM at 100km/h |
|---|---|---|---|
| First Generation | www.classicjalopy.com | ||
| 280SL (107.042) 280SLC (107.022) 5 Speed Manual (to June 1976) HK RSA (to May 1976) | 3.92 | 31.7 | 3155 |
| 280SL (107.042) 280SLC (107.022) | 3.69 | 33.7 | 2967 |
| 350SL (107.043) 350SLC (107.023) | 3.46 | 35.0 | 2857 |
| 450SL (107.044) 450SLC (107.024) To Dec 1973 | 3.07 | 39.5 | 2532 |
| 450SL (107.044) 450SLC (107.024) From Jan 1974 | 3.06 | 39.6 | 2525 |
| 450SLC 5.0 (107.026) | 2.72 | 44.5 | 2247 |
| 450SL (107.044) 450SLC (107.024) USA 1980 | 2.65 | 45.7 | 2188 |
| Second Generation | www.classicjalopy.com | ||
| 280SL (107.042) 280SLC (107.022) | 3.58 | 33.1 | 3021 |
| 380SL (107.045) 380SLC (107.025) (1980-1981) AUS, SE 1981-1985 | 3.27 | 37.0 | 2703 |
| 500SL (107.046) 500SLC (107.026) (1980-1981) | 2.72 | 44.5 | 2247 |
| 380SL (107.045) (1981-1985) | 2.47 | 49.0 | 2041 |
| 500SL (107.046) (1981-1985) | 2.24 | 54.1 | 1848 |
| Third Generation | www.classicjalopy.com | ||
| 300SL (107.041) | 3.46 | 35.3 | 2833 |
| 560SL (107.048) USA, AUS, J only | 2.47 | 49.4 | 2024 |
| 420SL (107.047) 500SL (107.046) | 2.24 | 54.5 | 1835 |
Excellent post
Would it be possible to swop a 420 or 500 diff into a 300SL
The V8’s used the bigger case, presumably for the torque. You would probably need the driveshafts etc.
Personally, I wouldn’t. The M103 doesn’t have the torque to drive a 2.47 ratio and certainly not a 2.24. I find even the 420 is a bit over geared and probably should have had a ratio like 2.82.
Not sure where you are located, but finding a 3.07 from a french market 300SE might be a better option?
OK thanks for the advice
Not being a diff / gearbox expert the smaller the number the less the revs for a given speed….
I am based in the UK
Do I replace the whole diff or just the gears inside?
Tim
OK thanks for the advice
Not being a diff / gearbox expert the smaller the number the less the revs for a given speed….
I am based in the UK
Do I replace the whole diff or just the gears inside?
Tim
Yes, the lower the number the lower the revs on the highway.
its possible to replace the crown wheel and pinion but not a simple job. Not sure if the V8 one is the same size as the smaller one.
I have a UK supplied 1981 slc 380 with 4 speed gearbox and the diff ratio is way too high, I want to be cruising at 80 mph all day at below 3000 rpm so sounds like I need to find a 2.47, or should I go for the lowest at 2.24?
I would go with 2.47 or even 2.82 off an early 500SE. I think 2.24 would be too tall for a 380
Hi there very interesting read. I stumbled on this chasing options to bring down the engine rpm on my W115 “74 240D, I recently done a engine swap to a 4M40 turbo engine the conversion was a lot of work but came out great and suit the car very well it is great to be able to keep up to traffic. The Mitsubishi max torque is at 2000 rpm though and with the standard gearing sitting on 3200 rpm at 100km/h and would love to bring that down looks like according to the work done here the ratios that will get me there will be the 2.65 or 2.72.
The cars that came with these ratios is just very very very scares in Australia. Is there any body with the knowledge to advise if I’d be able to change the crown wheel and pinion over in my diff if I can source them ??
Thanx Dutchie
Hi there!
Do you have all technical data for rebuilding one?
Something genuine manual from MB.
I am planning to rebuild mine that has wasted clutch pads
but i don’t have any data regarding torque values, etc
Many tahnks
Sorry I don’t have a rebuild manual for a diff.
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