15" wheels should help the MPG on my 300TD I mounted 15" steel rims with 205/75 tires. The RPM dropped by 10% so I hope I get some better than 20MPG. The ride is super nice on the highway and the tires are stiff enough for stability.

1. What differential could I use for better gear ratio??
2. In what other models can I find that differential ?

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Good Patina Comes With Good Miles Driven.
Drive more polish less

220SEB 1963 (excellent driver with no rust but far from pretty)
300 TD Wagon 1981 (Daily Commuter Tractor)
911 MFI 1973

www.vintagemotion.com

2.88 that was used on the '85 w123 and w126. You will need the '85's speedometer as well.

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RRGrassi


70's Southern Pacific #5608 Fairmont A-4 MOW car

13 VW JSW 2.0 TDI 193K, Tuned with DPF and EGR Delete.

99 W210 E300 Turbo Diesel, chipped, DPF/Converter Delete. Still needs EGR Delete, 232K

90 Dodge D250 5.9 Cummins/5 speed. 400K

Gone and still missed...1982 w123 300D, 1991 w124 300D

What ratio does my 1981 300TD wagon have now?

__________________
Good Patina Comes With Good Miles Driven.
Drive more polish less

220SEB 1963 (excellent driver with no rust but far from pretty)
300 TD Wagon 1981 (Daily Commuter Tractor)
911 MFI 1973

www.vintagemotion.com

I'm guessing 3.07. It is stamped on the bottom of the rear diff, I just do not remember if it is the left or right corner. You can see it just below the rear diff cover. Of course it needs to be cleaned to read it.

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RRGrassi


70's Southern Pacific #5608 Fairmont A-4 MOW car

13 VW JSW 2.0 TDI 193K, Tuned with DPF and EGR Delete.

99 W210 E300 Turbo Diesel, chipped, DPF/Converter Delete. Still needs EGR Delete, 232K

90 Dodge D250 5.9 Cummins/5 speed. 400K

Gone and still missed...1982 w123 300D, 1991 w124 300D

If you're getting only 20mpg then you're either driving it VERY hard or there are problems dragging down its efficiency.

Search the forum for suggested maintenance points.

I don't think mpg is as related to rpm on a diesel as it is on a car. It takes a set amount of POWER to move the car x distance at y speed based on the rolling resistance of the tires and aeordynamic drag. That power requirement when factored with the efficiency of the engine gives fuel economy.
Increased resistance in any way (dragging brakes, added roof racks, who knows what else) will decrease economy, so will decreasing the efficiency of the engine with things like bad thermostats.

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Sadly Benz-less

The efficiency on internal combustion engines is highly depended RPM. If to low the efficiency is bad and if to high the efficiency is bad. I commute 35 miles each way and a speed on 75-80 MPG. The engine refs 3000-3500 RPM.

Next week I will try my MPG going no faster than 65...we will see.

Still hoping to find a 2.88 axle ....would a 300SD axle fit?

__________________
Good Patina Comes With Good Miles Driven.
Drive more polish less

220SEB 1963 (excellent driver with no rust but far from pretty)
300 TD Wagon 1981 (Daily Commuter Tractor)
911 MFI 1973

www.vintagemotion.com

not sure this works out, at least not for me. I dropped my RPMs by a whole gear and I gained 2-3 city(so far) 5 hwy(estimated due to past difference, I will know when the snowbirds go home) MPG going from the 3.07 to the 2.47.

the 2.47 I have is from a w126, you just have to flip the rear mount. also, when you pull the rear make sure you keep the axles shims as they are sized to the diff.

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1982 300CD Turbo (Otis, "ups & downs") parts for sale
2003 TJ with Hemi (to go anywhere, quickly) sold
2001 Excursion Powerstroke (to go dependably)
1970 Mustang 428SCJ (to go fast)
1962 Corvette LS1 (to go in style)
2001 Schwinn Grape Krate 10spd (if all else fails)

you need to calculate your effective gear ratio. if it actually reduces rpm 10% then the actual mileage is 22. likewise the speed will be higher so if it reads 60 the actuak would be 66.

the 81 is na so the diff would be 346.

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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.

Look in the resources tab above and click on DIY articles. A good write up on R&R a Diff.

See Post #2 above for 2:88.

Charlie

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there were three HP ratings on the OM616...

1) Not much power
2) Even less power
3) Not nearly enough power!! 240D w/auto

Anyone that thinks a 240D is slow drives too fast.

80 240D Naturally Exasperated, 4-Spd 388k DD 150mph spedo 3:58 Diff

We are advised to NOT judge ALL Muslims by the actions of a few lunatics, but we are encouraged to judge ALL gun owners by the actions of a few lunatics. Funny how that works

For the 300D/CD, yes. The 300TD was the first non-300SD turbo in 81 so it should be 3.07.

On your picture it looks like you have bigger wheels as well. How does the 2.47 drive and from which car did you get the axle???

__________________
Good Patina Comes With Good Miles Driven.
Drive more polish less

220SEB 1963 (excellent driver with no rust but far from pretty)
300 TD Wagon 1981 (Daily Commuter Tractor)
911 MFI 1973

www.vintagemotion.com

I LOVE the 2.47. The only drawback is my speedo is off by 40%. also the wheels are large but the tire OD is actually smaller so that makes the 2.47 a little higher. I have a manual trans so an auto probably wouldnt notice the 1st gear takoff sluggishness I have. once I get to 5MPH first is like 2nd gear used to be and 4th is like an overdrive

I was watching my speedo closely with regard to RPM, this is what I have. At 45MPH (corrected to 63MPH) I turn 2200RPM. I think I have mis stated this in the past because I was guessing but this is the right numbers verified today. 4th has all the power I need to climb hills and will accellerate just fine. If I need to pass 3rd is the same as 4th used to be

I took the 2.47 from a 380 or 500 sel I cant remember.

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1982 300CD Turbo (Otis, "ups & downs") parts for sale
2003 TJ with Hemi (to go anywhere, quickly) sold
2001 Excursion Powerstroke (to go dependably)
1970 Mustang 428SCJ (to go fast)
1962 Corvette LS1 (to go in style)
2001 Schwinn Grape Krate 10spd (if all else fails)

We need a full write up thread with pics on this! I may be moving in that direction with my sonic wagon.

Your example has NOTHING to do with the rotational speed of the engine and EVERYTHING to do with the force needed to push the car through the air. Force required cubes with the square of speed. Less speed = less force, less force = less fuel. Your mileage will rise significantly at 65mph vs 75-80 mph.

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Sadly Benz-less