mgw_300e

I didn't want to hijack Chris' speaker thread, but I have some questions about differentials, and you seem to know a little about it:

I may need to replace the diff on my 2.8L 300e and I was thinking that a mod liek you mention for the 420 would be possible for the 300, but I don't know what ratio would be better for more torque / better performance. Do you know which would be the best diff for the 2.8L and what model I would get it from?

Eliot

The 400/420 is unique unfortunately, I believe you have a 3.07 gearing. Going higher will probably slow your acceleration (you spin through the gears too quickly.) It would also reduce your top speed. There may be a limited slip differential available for the 300E but I don't know if it would provide better performance. I haven't seen the manual and automatic 300Es compared but the first is bound to get a better launch. You might want to check on that

The 400 ended up with the 2.24 due to American fuel economy regulations. In Europe it came with a 2.65 differential and larger tires. The lower gearing took about a second off the the 0-60. Those who have tried the 2.82 have gotten sub six times.

neanderthal

these were posted by an aussie fella so the different markets may be different.

i think you have the 3.07. the coupes and the wagons should ahve the same axle ratio though, so if you get one of those, you should see better pick up/ worse fuel economy.

CDP

Eliot, How much does the 2.82 Differential cost?

Eliot

Depending on the car you pull it from, 250-350 plus shipping.

mgw_300e

so how does the gear ratio change the performance? What effect does going up or down in ratio have?

I guess what I mean is, should I look for a higher or lower number from my stock diff to enhance performance?


Another question I have along these lines is that if my problem is the trans, are all of the w124 trans going to be compatible with my engine, or only the trans that came with the 2.8L? I'm asking for two reasons; first is availability - a single year of production for the 2.8L limits the supply, and second - when I was into VWs, I remember people talking about swapping to the trans that came with the diesel engine because it was geared to boost the torque of the weak diesel engine. Is there such a trans when it comes to the w124?

Eliot

Mercedes just had the one automatic transmission.

As long as you have the straight six engine the manual shifter should mate to it.

mgw_300e

I am finding trans codes 722.3 - 722.5 were stock on w124s

what's the difference between the three?

neanderthal

im pretty sure theres a schematic on howstuffworks.com, i just cant remember.
think of it like a ten speed bike. the bigger the rear gear, the more you have to pedal, but you can climb pretty easy. the smaller the rear gear, the harder it is to climb, but you pedal less.
the higher the number, the more the ring gear turns relative to the pinion gear and the lower the gear. odd, i know, but the lower the gear, the more your engine spins therefore in this case your engine spins at a higher rpm. which is the desired result since you want to get into the meat of the power band.

so if you have a diff with a 3.07 ratio that lets you spin 3000rpm in top gear at 70mph and swap that diff with a (numerically lower,) ratio, then what happens is that at 70 your speed stays the same (duh) but the rpms drop, so you might be running 2600 instead. the reverse is true you install a 2.82 instead of your 2.24, then you are looking at much better acceleration (remember the big gear analogy with a bike?) but higher rpms when cruising.

i think that was more complicated than it had to be. but you get the idea.
if you do a lot of driving, especially freeway driving, you probably would rather go for the 2.65 instead of the 2.82. you will get slightly better performance and wont hurt your fuel economy that much.

722.3- 722.5 are different transmissions that benz used over the years. the .5 had an electric overdriven 5th gear and was found in all 6 cylinder R129s and W140s with an auto transmission. some R129s came with a stick, all were 6 cylinder.

as for swapping them, youll have to consult a pro here. i believe they were all the same, gear ratios and everything between all the different classes of car that used a given transmission, but the bigger engines had more clutches and perhaps bigger brake casings internally. like is said consult a benz pro. obviously there will be differences between a 722.4348 and a 722.4586 (i made up the numbers, but you get the idea.)