I believe my 81 300SD is equipped with a 3.07 rear axle ratio, what are some pros and cons of switching to the 85 2.88 rear end? I would like lower crusing rpms and better fuel economy. If anyone has tried this, what are you seeing? Will the car feel considerable slower? I have also heard that the 85 2.88 uses a different mount than my 81 w126 does. I am just trying to decide to bite the bullet and do the swap when I am changing my CV boots...


Thanks for ya'lls input.

Ian

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Regards,
Ian White

1995 E300 Diesel w124 OM606
2014 E550 w212 M278 biturbo

2001 BMW 740i E38 M62 (past)
1981 300SD w126 OM617 (past)

I went from a 3.07 to a 2.88 in my 83 300D about two years ago. (just sold it recently) I would certainly recommend this if your objective is altering top speed.

Gave me a somewhat higher top speed and somewhat less acceleration. I did it for highway cruising, so it made sense. The rear end combined with taller tires resulted in a speedometer discrepancy of 8-10 mph faster than with the stock 3.07 and original tire size.

I did not notice any appreciable difference in fuel economy though. It was about the same with both, although both were low since I have a lead foot in general.
Also, I pulled my 2.88 out of a 1985 300SD and it bolted right up to my 1983 300D, so I would imagine that it would be the same as your earlier 300SD. Only difference was that the new diff had a port for ABS which I capped off.

There was a difference in acceleration, but honestly, it was barely noticeable to me. The car did have a 4-speed swap with both ratios. I don't race or measure quarter mile at all, so I was perfectly happy, but if you do, you may not want to do it.

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The '85 is the last year that will bolt up. You should be fine.

Ive got a 79 116Sd 3:07 and an 85 TD 2.88. I can notice the difference in acceleration. Never compared the fuel economy. I'm in Colorado. In the mountains I think the 3:07 is preferable. For long flat drives the 2:88 is preferable. Not a big enough difference for me to consider swapping one out for the other.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

I swapped a 2:88 for a 2:88 a few months ago. I did not notice much difference...

Seriously though, it would depend on your driving habits. I actually thought about putting a 3:07 in my 85. But, in the end I went with the 2:88 again because I do 60 MPH driving up in the rural part of Brevard county. The lower RPM's when you approach 70 MPH is nice with the 2:88.

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AJ

1985 300D (SOLD)

I swapped the 2.88 into the SD a couple of years ago, primarily to reduce rpm's on the highway.

I'm quite pleased with the results. My typical cruising speed is 67 mph with the SD and it is perfectly quiet at about 2800 rpm. Increase to 70 mph, however, and the noise level increases markedly.


Cannot comment on fuel economy as the change was made at the same time the head was replaced. Current fuel economy with winter fuel and 90% highway miles is approx. 27. It can get close to 30 in warmer weather without the a/c.

It does suffer a bit on hills, however. The rpm must be maintained above 2700 or the available power is not sufficient to maintain speed. It does appear to have more torque at 2800 than it does at 2500...........in contrast to the specifications for the vehicle.

Exactly!

That is what we do. Anything over 70 seems a little noisy and uncomfortable. The car can easily do it... BUT, it just feels better around 67-68MPH.

You can probably "hear a pin drop" in the SD at those speeds.

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AJ

1985 300D (SOLD)

My thoughts exactly with my '85, minus the fact mine has it factory. 65-67mph is the ideal cruise speed with the 2.88:1 diff it appears.

My fuel economy is very similar to this also, have not kept up with it in years but from memory I would receive what BC is reporting.



It has been years since I drove a 617 with a 3.07:1, but it did not feel much quicker if at all between the two. I do not see the taller 2.88:1 changing performance enough to care, the car has 123hp. It was probably installed to reduce engine noise more than to increase economy or lengthen engine life.

If you can deal with downshifting on the freeway to climb a grade or if you can deal with slowing down without downshifting (like me), consider a 2.47:1. Perfect gear for driving in the city in 3rd gear, this yields around 2200-2500rpm (depends on converter slip and load) around 45mph and around 2400-2600 at 65mph freeway.

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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]

One wagon has the 3:07, one has the 2:88. Not really enough difference to go through the swap just for the sake of trying to change something. Now if your 3:07 rear end went out or was making noise, I would probably look for a 2:88 in that scenario. But again, not really that much of a difference.
FYI, I can't compare rpm's since 81's don't have a tach.....

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Jimmy L.
'05 Acura TL 6MT
2001 ML430 My Spare

Gone:
'95 E300 188K "Batmobile" Texas Unfriendly Black
'85 300TD 235K "The Wagon" Texas Friendly White
'80 240D 154K "China" Scar engine installed
'81 300TD 240K "Smash"
'80 240D 230K "The Squash"
'81 240D 293K"Scar" Rear ended harder than Elton John

I'm with Jimmy on this one. Also, over the 20 years of owning 617 powered MBs, a 3.07 '82 SD gave me the best fuel mileage.
2.88 cars are a little less noisy on the hwy.

Hello, I had a 3:46 diff in my 1980 wagon that had a turbo motor swapped into it from p.o. I too did the axles and thought it would be a good time to swap diffs and I happen to have a spare one from an 82 300SD. It was 3:07. I cleaned it all up and primed and painted it chevy orange so if it did ever leak, it would be easy to see. I would have painted it white but did not have any. (paint with old seals in, then cut around the seal edge with an exacto blade so as not to peel the paint off when removing old seals)

I also put in new axle seals since it was alot easier to do with the diff on the bench.(plus the left seal shattered when I did the axle the first time...-40 degrees celcius.) I bought a pinion seal but could'nt figure out how to get the strange bolt off there without having to get a special tool. I still have the brand new pinion seal somewhere. Filled with Amsoil synthetic diff fluid. Looks nice. I get a better top speed on the highway with way less noise.

We also have a 1985 wagon with the 2:88 diff. I do not notice much of a difference except that strangely enough the 80 wagon (3:07) gets better fuel mileage. The 85 seems to have way more off the line as well, which also is kinda backwards. I do think I have some issues with that 85 though so maybe not a fair comparison. maybe issues with the 80 as well...don't seem to get as much boost. problems in different areas.

Both the cars are primarily highway drivers on the flat prairie. When originally planning to do this swap I was actually looking for the 2:88 for the 80 wagon as per this site. I spoke with the Mercedes mechanic I get my parts from and he told me to go with the 3:07 to keep revs up, plus I already had the 3:07. I am always glad when I listen to him.

I had to drive the 85 on some slippery roads this winter and I must say that I hate where the boost comes on for the 85 (2:88) as compared with the 3:07 but as I mention previous I think the 85 has more boost for some reason and that seems to break the tires loose in all the wrong places as per shift patterns. The 85 (2:88) has winter tires and the 80 (3:07) does not....also strange and backwards from what I would have thought.

I wonder if the transmissions were geared differently if the car got a 2:88 from the factory?
I would go with the 3:07 again if I had the choice which may not be fair considering the problems forementioned with each of the cars. Oh yes,and I believe the p.o owner put a brand new head on the 1980 before I got it.
He spent alot of money on it considering how much I paid. (less than the cylinder head cost him) The 1985 wagon looks untouched from new except the bills seem to indicate the car has gone through three new timing chains within only a few years?

either one is better than the 3:46....very loud at 120kms/hr.