Looking for some feedback. I would like to increase the MPG on my '99 E300TD.

Like the performance, however I think with the 5-Speed the performance would not suffer much if I changed the rear diff to a lower ratio. I spend a lot of time between 65 and 75 mph and would like to decrease the engine rpm.

Currently it has a 3:42:1 rear end. I'm thinking about a rear end from an E430, which uses a 2.82:1. Another option would be an E320 diff, which uses a 3.07:1.

The route I travel every day is very flat, plus I figure if I ever needed extra performance I could always drop it into 4th for a 1:1 transmission ratio. If you look at the old '86-'87 300TD's and the 190 2.5TD they all had a 2.65:1 ratio, so why not use that on a newer diesel?

Thanks for the inputs.

the older diesels all had a direct top gear. the five speed is I am sure an overdrive.

In my experience changing rear ends has almost always resulted in better fuel economy. As the cars become more sophisticated like yours, I would expect the benefit to be less. If you decide to change it I would recommend caution and not go with a drastic difference, keeping to a maybe 5 to 10% difference from the factory ratio.

Tom W

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Am wondering what the ECU is going to think about that?

Engine and trans would be moving in same relationship to each other but speed sensors would be going faster than they are supposed be going.....

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Terry Allison
N. Calif. & Boca Chica, Panama

09' E320 Bluetec 77k (USA)
09' Hyundai Santa Fe Diesel 48k (S.A.)

I don't think there would be a problem with the ECU. All the car has is ASR and I think all that uses is the ABS sensors on each wheel and nothing drive train related.

The speedometer/odometer would be off, but with today’s electronic speedo's I think that could be adjusted.

I may be wrong but don't think the ECU would be a problem -- but I could be wrong.

Thanks for the inputs -- looking for more.

I have thought about doing this change myself. I think the reason for the stock (numerically) higher final drive- 3.42:1 is for the "performance craving" Americans. The diesels they sell here MUST have performance close to the gas cars, or they won't sell as well because they'll be perceived as a "sluggish diesel" like they were in the '80's.

Given I'm doing 0-60 in the mid 7 second range now, I would happily give up some performance to pick up say 3 to 5 mpg.

Assuming I'm doing the calculation correctly, to go from the stock E300TD's 3.42:1 to the E320's 3.07:1 is about a 10% reduction. If this percentage translates directly to engine rpm reduction as well: since my car with the stock gearing at 55 mph yields about 2,050 engine rpm. With the 3.07 ratio in place, the rpm at that speed would drop to about 1,850 rpm.

Furthering this, with the E430's 2.82 ratio, the reduction is about 17.5%, so the engine rpm should fall to about 1,700 rpm at 55 mph.

With the torque that this engine has, I can't imagine it would be lugging even with the 2.82 gearing, though you would probably see a little more turbo lag due to the lower initial engine rpm upon acceleration...

Would an E430 diff just bolt into the place of my current diff with no other changes? If so, I may put this close to the top of my "to do" list!...

Additionally- I'd assume that the engine rpm reduction would yield a similar percentage error in indicated speed on the speedo... Would changing to an E430 speedo solve this, or is a "black box" adjustment required since it is an electronic speedo?

Sounds like a very worthwhile swap. I agree the diesel torque will carry the car well.
I believe the speedo can be swapped unless its electronic. look at a speedo from the donor car. I've used a E320 in an '87 300D successfully, both mechanical speedos.

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'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body, '87 300D Sportline suspension, '79 300TD w/ 617.952 engine at 367,750 and counting!

Clusters are not plug and play to the best of my knowledge.

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Terry Allison
N. Calif. & Boca Chica, Panama

09' E320 Bluetec 77k (USA)
09' Hyundai Santa Fe Diesel 48k (S.A.)

Actually, your speedometer and odometer would not be affected.

Unlike older cars, the 210 gets the speedo signal from the ABS.

That's nice to know...makes things even more simple!

J.G.

The main problem with the 430 diff would be the eight-hole guibo. You'll have to unbolt the part which goes to this from your differential to install on it. I'm not sure that this doesn't involve setting the pinion bearing clearance with a crush tube.

You might try borrowing a larger set of rear wheels/tires. This would give you the effect of lowering the gear ratio. That way you could see if you like it. Measure the two different tire's roll out (straight line one turn circumference length) between the different diameter tires and mathmatecialy interpret that to the "new" lower gear ratio.

Example.... if the length of old tire run out to new tire run out is maybe 80%, then 80% times the existing car gear ratio gives you the new gear ratio. It is quick, non permanent, and can get you going in the right direction.

Regards

Run-Em

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1983 300SD - SPARKY THE DIESEL
2004 Audi TT 3.2 Quattro Roadster
1999 SLK - aka - LIL RED
1956 Chevy Nomad - aka - REAL MAD
1940 Ford dbl dr. Deluxe - aka - ORANGE U GLAD
1998 Kawasaki Nomad bike --

Please correct me if I am wrong but...

Why does my 99 turbo run less rpm at 75 mph than the 87 turbo I had?

Please confirm but I believe at 80 mph I am running 2800 rpm. I believe my 87 would run 3000 rpm at 80 mph.

87 is 1:1 4th with 2.65 rear

99 is .83:1 5th. How can it have a 3.42 rear because .83 of 3.42 is 2.83 which is steeper than the 2.65?

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-disav

99 E300 TURBODIESEL Astral Silver 282K - AMG brakes, suspension, monoblocks, speedo & interior - Full Load Maxed on IP by custom Speed Tuning USA Chip - T3/T4 Garrett - EGR/MAF delete
98 E300 TURBODIESEL Alexandrite Green on black leather 289K
95 E300 DIESEL Green Queen 267K SOLD
84 300D 216k SOLD
87 300D 299K #22 head - intercooler - full load adj. - 8sec 0-60mph - SOLD
76 300D 214K SOLD

Get an Ultra Gauge to monitor your MPG and throttle position in real time.
UltraGauge Automotive Information Center and OBDII Scan Tool

Put more air in your tires.

You can easily achieve the 10% MPG increase you are looking for.

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Greg
2012 S350 BlueTEC 4Matic
2007 ML 320 CDI
2007 Leisure Travel Serenity
2006 Sprinter 432k
2005 E320 CDI
1998 SLK230 (teal)
1998 SLK230 (silver)
1996 E300D 99k, 30k on WVO
Previous:
1983 240D, on WVO
1982 300D, on WVO
1983 300CD, on WVO
1986 300SDL 237k, 25k on WVO (Deerslayer)
1991 350SDL 249k, 56k on WVO - Retired to a car spa in Phoenix
1983 380 SEC w/603 diesel, 8k on WVO
1996 E300D 351k, 177k on WVO

at 80mph, the 87 Torque converter is slipping around 10%, and the tires are likely smaller on the 87 than the 99.

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 560SL convertible
1987 190D 2.5-5SPEED!!!

1987 300TD
2005 Dodge Sprinter 2500 158"WB
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

Please keep us up to date on results if you do the rear end swap, i am very interested in this

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Courtney
2006 E320 CDI
2008 ML320 CDI