renncpe

I just had a 3.69 differential installed today it’s out of a C240. The stock one in the Coupe is 3.27. Results it’s raining I can’t tell you any numbers but the seat of the paints feeling is BIG difference. We thought there would be a problem with the ESP system and were prepared to battle that but we found no problem. Because it’s a stick and not auto the computer does not know what gear you are in. We have not tried an auto so we really don’t know how it will react.

Randy

JustinTRW

Do you know how much top end speed you've lost? I assume your top speed is significantly lower.

Justin

renncpe

The car is limited to 130 before I could get there in 5th, now I will have to shift to 6th. I'm sure I lost some but I don't get the oppertunity to use it any way.

Randy

JustinTRW

That's true....us American's don't get that many opportunities to hit 130.

Flashman

Randy,

Can you explain a little on the advantages of the different ratio? I'm curious to understand this a little better.

renncpe

By using a higher gear ratio in the rear end (differential) it gives the engine a mechanical advantage over inertia. The engine will turn faster in relation the ground speed. The speed in gear will drop, as will the time to achieve that speed. I can still hit 60 in third gear as before but I will get there quicker.

Randy

gab

will this screw up the speedometer?

gab

This is from the Dinan Site:

Dinan offers a 3.15 differential for the 330, featuring a shorter final drive ratio. The 3.15 final drive gearing takes advantage of torque multiplication, lowering the stock 2.93 gearing for a 7.5% increase in torque delivered to the ground. The improvement in acceleration comes with only a minor increase in engine speeds at cruise and no effective reduction in top speed.


Looks like from 3.27 to 3.69 is quite a lot?
1st and 2nd gear of the C Coupe is already very short so its like I can only hit 40mph in first gear with the upgrade.
its almost equivalent to decreasing the wheel diameters by 1.5 inch-2inch??

gab

with the upgrade, what is your engine rpm at 6th gear cruising at 80mph?

goodkat

Randy, will you be putting the car back on the dyno to measure the increase in power and torque? And is this upgrade as simple as purchasing the 3.69 differential, removing the 3.27 and having the 3.69 installed? How much is a 3.69, and how long does it take to swap them? As always, thanks for the info

Larry

renncpe

I checked last night @ 3000 RPM I was at 67 mph in 6th gear.

Randy

renncpe

The change will not actually increase the HP or torque of the engine. It’s an increases mechanical advantage (leverage) of the drive train.

Randy

NJPaprika230

On my drive home this morning, I was doing 80 mph @ 3000 rpm in 6th, but that's with the stock 3.27 gears. Also, Randy, are you sure they were 3.69 gears from a C240? I checked all over the MB-USA site for present and past models and did not find any C class cars with 3.69 gears.

Ed

renncpe

Right I was 67 mph @ 3000 RPM. I don't know we got the part from patomic, checked the part number and came up with 3.69 in the MB computer.

Randy

Buellwinkle

RennCpe,

Are the gears installed directly into the rear end housing or is the pumpking removable? Can my local speed shop that specializes in american rear ends be able to do it?

renncpe

We just changed the whole pumpkin, it was much quicker and did not require any special tools. maybe 12 bolts holding it in most are for the u joint.

Randy

patronus

If you do not mind my asking, what did this cost you?

Buellwinkle

Can you buy the pumpkin from MB already assembled or did you get one from a salvage yard? And what did it cost?

gab

i wish they make one between 3.27 and 3.69
cos the c coupe gears already quite short
perhaps i could start in 2nd with the upgrade

looks like i wasted some fuel economy at 67mph with 3000rpm

what about a lightened flywheel? i wish the c coupe could rev as fast as an audi tt

renncpe

It was a used part it was 500.00 plus shipping.

Randy

TimmyC230boy

I drove a TT this week. yes, DON'T WE ALL wish it revved as fast. Ever driven a S2000, I drove my friends and it revs even faster. I still prefer my Mercedes though.

Lynn

According to my C-class brochure, the C240 has a 3.46:1 differential.

renncpe

The standard ratio is 3.46. I'm trying to confirm just what I have. The number crossed to a C240 3.69. What calculation can I use to make sure? 3.27 to 3.69 are a 12% difference 3.27 to 3.46 is 6 % difference. I will play around with it tomorrow. I have to measure my roll out on the rear tires. And get some trap speeds.

Randy

Buellwinkle

It has tough digging but I found what might be the only 3.67 rear end axle ratio to come on a C-Class. It's on the automatic C180 sedan in Australia. Doesn't exist on any of the C class in the U.S. or Canada, at least on their website and most other countries don't give rear axle ratios info on their sites.

I replaced my 2.73 with a 3.45 rear end on my daughters 98 Mustang, a more significant jump and it was great, best $350 performance investment I made (for a used set installed). Gas mileage and the higher freeway revs where not impacted significantly. It would be a way more significant seat of the pants difference than chipping or even a pulley. I would do it for the coupe depending on the costs of the gears and then finding someone to do it. It helps that you can pull the pumpkin out and work on it on a bench. Ford ring and pinion gears new are about $175 and it's about $200 to 250 labor to put them in (not a DIY project). While MB stuff can sometimes be pricey, this may not be that expensive. Has anyone checked? Also there are discount dealers like Hoehn in San Diego. I would get the highest they have, heck 4.10s if they had them.

The problem is the speedo calibration. This likely can't be a $5 plastic gear in the speed sensor like on the Mustang. How does the factory compensate for different wheels/tires, is there a computer setting they can set?

Lynn

Randy, I was just anwereing gab's question about whether there is a ratio between the 3.27 and 3.69. I was not questioning what you had posted.

A quick way to check the approximate ratio is put the car on a lift. Mark the tire, and the dirveshaft. Turn the driveshaft on revolution, and count how many times the tire turns.

For those who don't have ready access to their references the formula for gear ratio is:

(RPM x Tire Diameter x 2.96) / (1000 x MPH)