I am considering changing the rear differential in my 84 300SD from 3.07 to 2.47. I read the threads here with great interest and learned a lot, but have some unanswered questions. I am interested in hearing follow-up from people who have made this modification:

1. Gas mileage - how much, if any, did your mileage improve with the 2.47 differential.
2. Installation - I know you need to remove the halfshafts from the diff, but do you need to remove the halfshafts from the wheel hubs?
3. Installation, part II - Can one simply unbolt the flex disc from the diff, or does the 'gland nut' on the driveshaft need to be loosened (that's the procedure according to the FSM).

I am most concerned about increasing the mileage. I am currently averaging 26mpg, but would like to increase that. On a recent 1600 mile road trip at 65-75mph, I averaged 22-24mpg.

Something is wrong with your 300SD...you should get atleast 26 and up to about 28 if you play it chill under 70mph and the roads are not 40% grade!

I can't get 22-24 if I try...

Maybe 24 if I really beat on it the whole tank

If you change the diff and you end up load your engine at low speeds and it is always downshifting...working harder..etc it will not pay off to put in this other diff.

Now if your car sees purely highway miles..it will help.

Mixed driving...you will just hurt your acceleration and your fuel mileage.

I would look at doing other things to the engine before you do this...mpg should be much better.

Not a 2.47 but I replaced the 3.07 in my sedan with a 2.88...saw slight improvement in mileage...on average, about 1 mpg better (this car gets driven almost exclusively in town) and no decrease in performance. Road trips are much nicer since the engine is no longer spinning 3400rpm at 75 mph. IMHO, It was definitely worth the effort since todays' highway speeds spin these engines way too fast.

Yes, remove the shafts from the wheel hubs. They will be in the way when you start monkeying around with the differential if you leave them in the hubs...

When you get ready to pull the axles, remember to raise the entire differential/subframe assembly up into its normal position. If you do not do this, there will not be adequate clearance to move the axles inwards and get them out of the hubs.

Yes, you will need to loosen the gland nut too (don't tell anyone but I use a pipe wrench on mine). Then just unbolt the flexdisk from the diff. Don't forget to push everything back into position and retighten that nut when you are done. FWIW, for some reason, one of my cars doesn't have enough clearance, even with the loose gland nut, to remove the drive shaft from the diff. On that one, I have to remove the bolts from the driveshaft center support and let the entire shaft hang loose in the tunnel.

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Never a dull moment at Berry Hill Farm.

I saw that! But I've done that too. Finally, I modified an old wrench for that. Ground the opening to 46mm and cut it short. Worth the effort. What a PITA it is with a pipe wrench by comparison.

Warning, hijack!!...who here knows which axles besides the 2.47 came with limited slip? If I ever do this swap my primary motivation would be for the LS.

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'82 300SD - 361K mi - "Blue"

"Good judgement comes from experience. Experience comes from bad judgement."

listen, look, .........and duck.

Thorsen,

I did this exact changeover back around March of this year. I would guess that I am getting maybe 1.5-2.0 MPG increase in highway driving. R Leo has nailed it on the facts of the installation.

Brandon, I would agree with you in theory as far as the additional (maybe excessive) shifting in town, but I have honestly not experienced this change in my 300SD. I can't account for why this is the way it is, but I will not complain about it. I don't understand why the 2.47 was not included in the factory package. Tremendous comfort change on the highway and no noticeable change around town. I still have been able to keep the 0-60 time just under 14 seconds. Last summer we took the car down through the Ozark Mountains. It was loaded to the brim with 2 people and enough food and beer for a week. No problems at all. I realize the Ozarks are not the Rockies, but it was a better test than the flat plains with which the car is accustomed . I do agree, by the way, that Thorsen's mileage is way too low and that there must be some other factors working against him there. I doubt that the 2.47 changeover will fix this issue.

Tom

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1993 300TE
1984 300D
1984 300SD
1976 BMW R90S

on the lessening of acceleration from a stop. but once you are rolling i dont see much difference, the car will just hold the lower gears longer and in traffic and such i doubt you will see much diff.

but on the fuel mileage, i think you will ALWAYS see higher economy with a taller gear in the rear end.

i have up geared at least seven or eight times. on a diesel it always works. usually does on a gas too, but on my 81 280e it didnt seem to work as well as i thought it would.

good luck!

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.

Hehe, for a while it seemed like I was spending more time under the backend of these cars than behind the steering wheel.

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Never a dull moment at Berry Hill Farm.

Boy I wish I could complain about getting 26mpg. With my 85' Kalifornistani emissions 300 SD I'm getting between 20 and 21 mpg. 50% of my miles are highway too. I know something is wrong, I don't know what though. I just know my 79 had alot more zip and a lot better milage.

How many Mercedes do you have?

There's a 280E with a 4 speed I want in town. It's a grey market one too. Have you driven a 300E to compare performance?

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I'm not a doctor, but I'll have a look.

'85 300SD 245k
'87 300SDL 251k
'90 300SEL 326k

Six others from BMW, GM, and Ford.

Liberty will not descend to a people; a people must raise themselves to liberty.[/IMG]

Perhaps...but gear ratios are not always the case of "the taller the better" heh

For around town driving you don't want to have to put your foot to the floor while the car tries to catch up.

no doubt that the torque converter takes care of the different diff on takeoff and then you reap the benifits when crusing. But just remember that a taller rear end is not always the best thing in the world. For example, extreme case, a 2.00 diff would be horrid

Well 1st gear is gone so quickly in these cars as it's so deep (what 3.8X:1 ?) I don't think we'll see a big difference going from a 3.08:1 or 2.88:1 as the first gear will be dragged out.

Not to mention you'll be able to cruise about in town in 3rd at higher speeds with the taller rear axle.

I finally have found an inexpensive 2.47:1 locally from a 560SEL that I'm going to throw in my SD. It seems to like lower RPMs. At some point I'll get one for the SDL.

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I'm not a doctor, but I'll have a look.

'85 300SD 245k
'87 300SDL 251k
'90 300SEL 326k

Six others from BMW, GM, and Ford.

Liberty will not descend to a people; a people must raise themselves to liberty.[/IMG]

three left that drive and my ex ralley euro 280e that has been flooded. but i have had 29 over the years that i remember. i got my first one in belgium in 1973. a 61 fintail 220b. my latest is the 90 350sdl. havent had an sl yet or a 500e. those are still on my christmas list.

my brother has the 280e with the 2.88 rear end. it is still plugging along.

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.

Oh wow

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I'm not a doctor, but I'll have a look.

'85 300SD 245k
'87 300SDL 251k
'90 300SEL 326k

Six others from BMW, GM, and Ford.

Liberty will not descend to a people; a people must raise themselves to liberty.[/IMG]

Brandon,

My mileage when I chill is in the 26-28 range. The 22-24 was on a road trip where I spinning the engine pretty fast. 80% of my driving is on the highway.

My lifetime economy is on the following chart http://www.pokrefke.com/benz/benzmileage.htm
The Nov 19-22 entries were on my high-speed trip.

Okay that sounds very reasonable.

I figured the trip would be "chill speeds"...not "brandon speeds"...ie...seeing if I can bury that 125speedo

Excellent documentation.