Does anyone know or have a link to the actual gear ratios used in the 7 speed transmission and rear end? I cannot find it anywhere in the owners paperwork.

I was screwing around with the car in manual mode and noticed 1st gear ran out of rpm's at a really low vehicle speed, something in the 20's it seemed.

The gear ratios are at the bottom. I hope this helps.

http://en.wikipedia.org/wiki/Mercede...c_transmission

Thanks. I had found another site with the gear ratios.

That site also listed the rear end ratio as 2.65 for a E550 coupe and 3.06 for a E350 coupe. I don't know if other body styles are different, which they may be, due to their higher weight.

I believe the rear end ratio you show (2.65) is for 2011 and earlier. This was discovered when we tried to put a Quaife limited slip differential (LSD) in our '12 E550C: the LSD used for the 2011 and earlier E550C will not fit. (Quaife was surprised too; they don't manufacture a LSD for the '12 at this time)
(a MBZ LSD unit for the C63 will fit, but the gear ratio is not compatible with the stock transmission computer program)

I'll ask the tech (who tried to do the installation) for the gear ratio, but it might be 2.47.
The Mercedes specs for the '12 show this: Rear axle ratio TBD.

Here's what MBZ shows for the '12 CLS 550 with the same engine: The 2012 CLS550 4-door Coupe offers 402 HP with 4.6L twin-turbo V-8 engine ... Rear axle ratio: 2.47

Was told that the higher ratio is because of the increased torque of the M278 engine and it also helps with highway MPG.

Possibly so. A CLS550 is about 10% heavier then a E550 coupe so maybe there is another ratio installed in the coupe.

What I find strange is the lack of readily available information about these car parameters from MB. Most every other car I have ever had published these figures right in the owners manual or other common manufacturer publications.

Maybe the average MB owner doesn't really care about the technical stuff.

As to replacing your rear end with one from another model with a different rear end ratio I would think it would be easy for one of the aftermarket companies program the computer to accommodate the different ratio. This happens all the time for other models. While their at it you could also get the 130 mph engine cutoff removed.

I agree and haven't found an aftermarket company to program it, but don't know if it's worth the warranty risk to install the C63 ratio (2.82-1), reprogram the trans, etc. No doubt the acceleration would be awesome, but the mileage would suffer.

Doesn't installing a different rear end i.e. limited slip result in the same warranty risk?

The other day while I was screwing around I put the car in 1st gear manually, on a relatively slick road and floored it from a standing start. The car hooked up and went arrow straight. Apparently the traction control is excellent and unless you are going drag racing, where you will power brake at the start, a limited slip may not be necessary. The outside temperature when I was doing this was 38 F so the engine was making a lot of power and the traction available from the tires was not all that great due to the low road temp.

As to drag racing with a limited slip I am no fan. The problem is unless you have the differential warmed up, the clutch packs don't provide the proper coupling. Their design usually requires an elevated operating temperature to close up the spacing of the packs. If you assemble the packs with less then spec spacing the differential becomes pretty much a no slip differential when warm and you tend to hop around corners like a spool rear end.

A long time ago when I was attempting to competitively race a LSD car, on several occasions I almost took out the tree and/or the wall several times. The solution was to put in a spool which solved that problem. For road use pack friction usually isn't a problem since you will probably have the rear end up to operating temperature. At the drag strip you can't depend on this as the time between rounds can be very long due to oil downs, amount of cars entered etc. This makes launching the car a real adventure since you never know if the limited slip is working or not.

The warranty issues aren't quite the same with just a LSD: then MBZ might not cover any failure related to the axle. With a different axle ratio, the engine will turn more rpm (quicker) which could create a problem if the engine or transmission failed and MBZ said it was because of the excess RPM or because of a reprogrammed trans....

The Quaife is a torsen style LSD and has no plates. Per Quaife: "I do know that the stability control system on MB cars can be upset by installing conventional LSDs, which is why the Quaife is so popular, because it doesn't trigger any issues".
I'm not planning to drag race, but it annoys me when the tire(s) spin and traction control kicks in. It happened last week on a dry road at 15 mph when I accelerated. Everytime traction control activates, the tires have already spun and of course this wears the tires prematurely. It was a huge problem on our SLK55 AMG.
Due

Most people who go racing, either drag or road, do not like the gear type LSD's but for the street they are a good choice.

As to installing the MBZ LSD with the lower gear I would think it would be possible to take out the ring and pinion and use the one that came with your car. Usually if a differential is the same size the gears are interchangeable although finding someone to set up a ring and pinion on a MB may take a lot of looking. I doubt if anyone at a dealership has ever done one. I've done quite a few ring and pinions but never an MB. I isn't that hard, it just take a little patience and some measurement tools.

My experience with the stock traction control and differential has been that the tires hardly spin if at all and I have tried as previously stated on really cold roads. I do have the stock tires Pirelli 255/35 H rated rear tires. Maybe they hook better.

I really don't notice any loss of low end performance or feel/hear wheel spin. The car goes through 1st gear such that it's kind of hit the gas and hit the up shift paddle almost immediately.

The MBZ dealer tech disassembled the differential and took measurements. Note: this tech is extremely qualified, has done many MBZ mods including differential setups, "tunes", and other.
To the surprise of the tech, the ring gear mounting flange on our '12 E550C is 5mm farther away from the pinion and the ring gear is thicker (compared to earlier E550C's). That 5mm is what prevented the Quaife from being installed. The measurements were sent to Quaife and they confirmed it would not fit.

Thanks for all of your input though!
Due

Can you make a 5mm shim to fit behind the ring gear to get it back in mesh with the pinion? This is a common procedure in a lot of race differentials where one is swapping parts from various models.

I just received information from a MBZ tech that the rear axle gear ratio for the 2012 E550C
is 1:2.47.

According to him the C, E, CLS, SL 63's (non-turbo) have a 1:2.82, although research has shown that according to Car & Driver (11.11) a 2008 E63 has a 1:2.70 ratio.

2011 and older E550C's have a 1:2.65 ratio.

Due