Better gear ratio for W123 Diesel – What axle would fit ?? - Page 2 - PeachParts Mercedes-Benz Forum

H-townbenzoboy · #16 11-15-2008, 01:57 AM

Quote:

Originally Posted by t walgamuth

Actually, according to my mb illustrated buyer's guide the cd was turob in '81 too. I wouldn't be surprised if it was a mid year change over.

There were no 1981 model year 300CD turbo diesels. All 1981 model year 300CDs were normally aspirated. Around 8/81 or 9/81, production switched from non turbo to turbo 300CDs, and while they made a few hundred 300CD turbo diesels in late 81, they were all 1982 model year vehicles.

rrgrassi · #17 11-15-2008, 02:45 AM

My 300D was assembled in 10/81. It is classed as an 82. It has the turbo.

t walgamuth · #18 11-15-2008, 09:44 AM

Quote:

Originally Posted by t walgamuth

Me either, thats why I quote the book. I do have an 82 300cd though. Its a turbo.

of course the coupes are even more rare than the wagons.

I seem to remember a road test of the first turbo and in my mind it was a coupe, but I have not searched for the magazine......it may be in a road and track in my basement.

I would have said neither the 126 msd, coupe or wagon came with the turbo to the states until 82.... but it may also be kindof a model year thing too....an 82 model year built in 81, though benz generally ignores model years.

I wrote this to respond to forced last night but forgot to hit submit apparantly.

curtludwig · #19 11-15-2008, 06:42 PM

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.

Quote:

Originally Posted by MercedesOtto

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?

winterbean · #20 11-15-2008, 07:33 PM

My '81 TD is most fuel efficient at about 50-55 mph--that's a little unrealistic for highway driving. Nevertheless, speed has a significant impact on mph.
RPM's definitely impact mileage, diesel or gasser--you can sit in your driveway revving to 3500rpm for 10 minutes and burn a lot more fuel than at normal idle.

MercedesOtto · #21 11-15-2008, 09:06 PM

Quote:

Originally Posted by lutzTD

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.

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???

lutzTD · #22 11-15-2008, 09:28 PM

Quote:

Originally Posted by MercedesOtto

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

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.

MercedesOtto · #23 11-15-2008, 10:31 PM

Quote:

Originally Posted by lutzTD

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.

Does the flexdisc fit from your car? I know that on gas cars different sizes are used from V8 to I6.

lutzTD · #24 11-15-2008, 10:34 PM

Quote:

Originally Posted by MercedesOtto

Does the flexdisc fit from your car? I know that on gas cars different sizes are used from V8 to I6.

I removed the 3 hole flange from the back of an old transmission I had and used it on the 2.47 from the SEL. I guess you can also use the one from the rear you remove but I wanted to keep mine intact in case I didnt like it or I wanted to put in a five speed

JackG · #25 11-16-2008, 08:00 AM

Quote:

Originally Posted by lutzTD

. The only drawback is my speedo is off by 40%.

Is there anyway to correct that?

lutzTD · #26 11-16-2008, 08:32 AM

Quote:

Originally Posted by JackG

Is there anyway to correct that?

I am looking at correction devices, unfortunately there is no cheap solution. there are mechanical ones with set ratios around $80, but Im not sure they will screw on and there are electrical drivers that are much more expensive but infinitely adjustable and again not sure if the threads are the same. I do the calc in my head for free

#27 11-16-2008, 10:10 AM

You can always get the speedo from an 81 300TD. Since its an electric drive (the only one in the W123 line for some reason...) it should be much easier/cheaper to alter it.

lutzTD · #28 11-16-2008, 12:33 PM

Quote:

Originally Posted by ForcedInduction

You can always get the speedo from an 81 300TD. Since its an electric drive (the only one in the W123 line for some reason...) it should be much easier/cheaper to alter it.

in all of my yard prowls to date, I have never seen an MB wagon. what about a later model speedo after 85? arent those also electronic? has anyone made a sender for one?

DeliveryValve · #29 11-16-2008, 01:48 PM

Quote:

Originally Posted by lutzTD

in all of my yard prowls to date, I have never seen an MB wagon. what about a later model speedo after 85? arent those also electronic? has anyone made a sender for one?

You can try to modify a 380SE speedo to fit in your car. Forum member Apotheoun did a version of this with his 300SDS had it done with his 4 speed conversion with magnets.

Quote:

...... There is a lot of thought planning and measuring twice involved before cutting. You will need to invent or create a home made rotational electronic pulse signal generator to run the speedometer, odometer, and cruise control, or you will have nothing to read on the dash.

This is the case with my conversion, which was finally made right. It formerly utilized a poorly hooked up 240D speedometer that was horribly inaccurate, and now it has a correct 300SD speedometer. To make it work though, Kurt had to invent a new signal generator by welding four magnets onto the drive shaft and attaching a nearby sensor, completely hand wrought. It works great, but nearly self destructed in the first two miles due to faulty clearances. The magnets are still bent over from the initial snafu, but work just fine. What a noisy racket that made!

lutzTD · #30 11-16-2008, 02:45 PM

Quote:

Originally Posted by DeliveryValve

You can try to modify a 380SE speedo to fit in your car. Forum member Apotheoun did a version of this with his 300SDS had it done with his 4 speed conversion with magnets.

yeah, not sure this will work for me, the 300CD uses a mechanical pickup for the cruise control and I would rather not lose that.