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Rear end swap
I am trying to get more top speed with less rpm in my 1980 300sd, I was thinking of maybe a 450sel same era rear end swap. Will this do what I need or what do I need to do ?
Thanks , Daniel
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Revenge is a meal best served cold 1980 300SD, Shotzie 1996 Volvo 850, Dark Night 1997 Ford F350 7.3, The Tuna Clipper |
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One year only, 1985 MB 2.88 diff, rare but available
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Do a "search" on the board for information.
M110 Engine Identification in my '74 w114 Sedan Post #10 As GRZPDLR notes, the 2,88 will be the "lowest" ratio which will swap into your existing differential housing (185 MM). You already should have the 3,07 so I doubt you would see much improvement. Numerically a 5% improvement but some of that will be lost in a lower efficiency at lesser rpms. Kind of a trade-off and it all depends on percentage of highway speed vs. in town use.
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“Whatever story you're telling, it will be more interesting if, at the end you add, "and then everything burst into flames.” ― Brian P. Cleary, You Oughta Know By Now Last edited by Mike D; 09-04-2020 at 04:57 PM. |
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If this is all about the ratio, then figure out what ratio you currently have first. It should be marked on the Diff. It’s an old car. It should have the originally optioned ratio, but you never know what it has now until you check.
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Past mb: '73 450sl, '81 280slc stick, '71 250, '72 250c, '70 250c, '79 280sl, '73 450sl, parted: '75 240d stick, '69 280s, '73 450slc, '72 450sl, |
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450SEL had a 3.07 or 3.06 axle except for the 1980 model year. Also I would trust mb engineers who designed this car and leave the axle stock. They knew that a taller axle would get them better fuel economy and less noise and yet they decided to stick with a 3.07 ratio |
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Quote:
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Only in the U.S. was the speed limit 55 MPH.
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“Whatever story you're telling, it will be more interesting if, at the end you add, "and then everything burst into flames.” ― Brian P. Cleary, You Oughta Know By Now |
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Exactly. In Germany where there were/are no speed limits in many places Mercedes used the same axle ratios as in the US |
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Yeah well, that's that fuzzy differential logic. A rough way to look at it is:
A "higher" differential ratio means the pinion gear needs to revolve more to turn the ring gear once. It takes 4,8 revolutions of the pinion to turn the ring gear once. This results in higher RPM's of the engine but lower revolutions of the ring gear/axles. Kind of like how when you are in fourth gear in a manual transmission. The input shaft is turning at a 1:1 ratio with the output shaft resulting in lowered RPM's but in first gear the ratio is more like 3,75 to 1.
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“Whatever story you're telling, it will be more interesting if, at the end you add, "and then everything burst into flames.” ― Brian P. Cleary, You Oughta Know By Now |
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In a 2.88, the drive shaft rotates 2.88 times for every one revolution of the axle or wheel.
If you are only looking to change from a 3.07 to a 2.88, why don’t you just put taller tires on? Get a tire that’s 6.6% taller than stock, and you effectively are doing the same. 205/70/14 —> 225/75/14 or 225/65/16 and you are getting 7-8+% more per drive shaft rotation. And it’s a lot easier than swapping the diff. Sent from my iPhone using Tapatalk
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Past mb: '73 450sl, '81 280slc stick, '71 250, '72 250c, '70 250c, '79 280sl, '73 450sl, parted: '75 240d stick, '69 280s, '73 450slc, '72 450sl, |
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agreed.
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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. |
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For example, a "Low" first gear provides a lot of grunt but tops out at maybe 3, 5MPH in a big rig. A high gear ratio is numerically low, but it allows for a higher top speed. I think this is where the high versus low comes from (your wheel speed is high or low). Think about 4x4s with "4 LOW" where your gearing is maybe 4:1, versus 1:1 of "4 HIGH" Anyway, I would suspect a 300SD is geared the way it is for a few reasons, one of which is potentially aero drag and horsepower. Would a taller gear allow you to go faster, or would the drag of the brick, combined with its lower horsepower, result in insignificant changes in top speed with a stiff penalty to acceleration and on-ramp performance?
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Current: 2021 Charger Scat Pack Widebody "Sinabee" 2018 Durango R/T Previous: 1972 280SE 4.5 2014 Jeep Grand Cherokee Limited "Hefe", 1992 Jeep Cherokee Laredo "Jeepy", 2006 Charger R/T "Hemi" 1999 Chrysler 300M - RIP @ 221k |
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Back when I had my 240D with 300D na euro motor with the 307 diff and five speed the car would run 100 mph in either fourth or fifth.
(for what it is worth). Where the taller gear helps is mpg which that car would do 40 mpg if driven 60 to 65 mph.
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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. |
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i have a 2.88 diff for sale in the parts section if you decide to go that route.
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1983 240d 5Sp SOLD 1986 300D(LUCO) SOLD 1983 300TD(dreamboat)SOLD 1984 240d (Executive)SOLD 1984 240d (Euripides) SOLD 1982 300sd SOLD 1982 300sd (Ambas)SOLD |
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