2.XX Axle Ratio for W116 with 617.950: - PeachParts Mercedes-Benz Forum

Doktor Bert · #1 05-12-2005, 01:11 PM

Driving my W116 with my modified 617.950 really is a lot of fun. However, I cannot help but think the 3.07:1 axle ratio could be better replaced with a 2.xx:1 variant.

Even with 205/70/14 tyres, the car just seems to want another forward speed.

What differential assemblies were available in the 2-Series that would bolt-in to a 1978 W116. Did any of these have a 2.XX:1 ratio???

With the modified turbo and fuel system, coupled with how the early 4-Bolt 722 shifts into low when you release the brake, I do not think the higher axle ratio would lug this engine at all.

Your input would be appreciated...Bert

boneheaddoctor · #2 05-12-2005, 01:16 PM

Funny thing is both of my Benzes in my sig have the 3.07 differential....both have 4 speed automatics........

Both have simmular diameter tires yet my W123 turns noticible far few rpms on the highway.........

ANd nobody can explain why................

But to the point...I am not exactly sure....and about the manual...get with me on email and I will see if I can make copies for you.

SYRacing · #3 05-12-2005, 01:23 PM

my 3.07 diff bit the dust with about 320k on it...got a different diff for free but its a 2.88
lost all my low end speed lol

t walgamuth · #4 05-12-2005, 07:53 PM

isnt that 79 a three speed auto? if so a higher gear will noticably reduce your quick takeoff as in crossing a street with traffic coming or merging, but if that doesnt bother you it will surely pull a higher gear on the hiway ok. see threads with a guy who put a 2.47 in his 300td. he is very happy with it and is getting well over thirty on the highway. personally unless i was doing almost all highway i probably wouldnt change it. no durability problems though i shouldnt think. also you'll need to change the speedo with one that matches the diff. probably can find a good used diff fror 200 to 300 and can pay to have it changed for about 300 to 250.

boneheaddoctor · #5 05-12-2005, 08:09 PM

Quote:

Originally Posted by t walgamuth

isnt that 79 a three speed auto? if so a higher gear will noticably reduce your quick takeoff as in crossing a street with traffic coming or merging, but if that doesnt bother you it will surely pull a higher gear on the hiway ok. see threads with a guy who put a 2.47 in his 300td. he is very happy with it and is getting well over thirty on the highway. personally unless i was doing almost all highway i probably wouldnt change it. no durability problems though i shouldnt think. also you'll need to change the speedo with one that matches the diff. probably can find a good used diff fror 200 to 300 and can pay to have it changed for about 300 to 250.

No...the '79 300SD is a 4 speed auto.....i've counted the shifts numerous times...........and the Manuals confirm it..............

Doktor Bert · #6 05-14-2005, 12:00 AM

Quote:

Originally Posted by boneheaddoctor

No...the '79 300SD is a 4 speed auto.....i've counted the shifts numerous times...........and the Manuals confirm it..............

The 722.120 Transmission (4-Bolt Pan) is indeed a 4-Speed, but it is not an overdrive. It is 1.01:1 in direct or 'high' range...Bert

Doktor Bert · #7 05-16-2005, 04:37 PM

Breckman:

I read that post. The ratio you are referring to is 2.47:1 or 2.65:1???...Bert

Benzcrusher · #8 05-16-2005, 11:45 PM

The diff from my 1979 450SEL parts car has a 3,08 diff......

jdblann · #9 06-05-2005, 09:16 PM

Doktor Bert,

I'll reply since no one seemed to answer your question. The 6.9 had a 2.65 ratio. I believe it would be a bolt in replacement for the 300SD.

I have thought about changing mine in my 1980 300SD along with the 6.9 cluster so the speedo will be correct.

Should make the 300SD cruise rather nicely.

Doktor Bert · #10 06-05-2005, 10:33 PM

Quote:

Originally Posted by jdblann

Doktor Bert,

I'll reply since no one seemed to answer your question. The 6.9 had a 2.65 ratio. I believe it would be a bolt in replacement for the 300SD.

I have thought about changing mine in my 1980 300SD along with the 6.9 cluster so the speedo will be correct.

Should make the 300SD cruise rather nicely.

Thanks for that information. It is appreciated greatly.

The cluster will not ensure correct speedometer calibration. That is controlled by the drive gears in the transmission...Bert

jdblann · #11 06-05-2005, 11:14 PM

I was under the impression it was the cluster. So does this mean I can change the ratio to 2.88 or 2.65 or 2.47 and change the drive gears in the tranny and get the speed to register correctly?

t walgamuth · #12 06-05-2005, 11:41 PM

in my experience with 115 and 123 cars the drive in the tranny is all the same and you need to swap out the speedo.

bonehead, if you have the same diffs and same diameter tires then the difference must be in innaccuarcies in the tach's. not really surprising. although i am always impressed in how accurate the mb speedos are.

boneheaddoctor · #13 06-06-2005, 12:03 PM

Quote:

Originally Posted by t walgamuth

in my experience with 115 and 123 cars the drive in the tranny is all the same and you need to swap out the speedo.

bonehead, if you have the same diffs and same diameter tires then the difference must be in innaccuarcies in the tach's. not really surprising. although i am always impressed in how accurate the mb speedos are.

Oh its not the tach.....the engines really are spinning a lot higher rpms....I still need to pull then pboth out onto the street jack a wheel up and count revolutions between the two....I suspect the 300D may have a rebuilt diff with lower gears as its quiet and smooth at 80mph and 3,000 rpm...the W116 is clearly winding up more RPMS...its smoother and more powerfull but also is audibly turning far higher RPM's....at the same speed....if I count the same revs at the wheel vd the driveshaft that will clear it up....becasue both should be identical. I do tend to believe the tach....my ears can pick the diffeences in RPMs pretty clearly...but counting wheel revolutions VS driveshaft revolutions is not going to be skewd by instruments that may or may not be accurate.

Old300D · #14 06-06-2005, 05:11 PM

Quote:

Originally Posted by Doktor Bert

Thanks for that information. It is appreciated greatly.

The cluster will not ensure correct speedometer calibration. That is controlled by the drive gears in the transmission...Bert

That's certainly not the case with my W123 240D. I swapped in a 2.88 rear end and the speedo was pretty far off, of course. I snagged a speedometer from an '85 300TD, and with no adjustments I get accurate miles and speed readings. I changed nothing in the transmission -- I also compared the transmission speedo drive gears between my 240D (with 3.69 originally) and an '82 300D (turbo, with 3.07 originally). They were the same diameter with the same number of teeth.

t walgamuth · #15 06-06-2005, 06:51 PM

bonehead, jack up one wheel (unless you have posi) turn wheel one complete revolution, count the number of turns of the ds and multiply by 2. or for more accuracy turn it 10 times.

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