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MECHANICALS With a 30 year-old automobile, there will always be discussion here - maintenance, modifications and mechanicals.

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Old 27th April 2016, 08:35 PM
aussie 6.9 aussie 6.9 is offline
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Default 450sl diff ratio

I recently acquired a 450sl w107 in addition to my 6.9. Although generally happy with it I find the gearing of 35km per 1000 rev a little low for my use. Does anybody know if it is practical to change the diff ratio.?
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Old 27th April 2016, 09:33 PM
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Default Re: 450sl diff ratio

I seem to recall somebody on another forum taking the diff from an early W126 380 and using it to lower the revs on the highway. Off the top of my head the 1st generation 126 fits but the 2nd does not.

keep in mind most aussie spec 450s had an LSD as standard whereas 380s did not....
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Old 30th April 2016, 05:18 PM
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Default Re: 450sl diff ratio

Mark, it's been done, but in the reverse. SEL69L had a 450 diff. fitted to his 6.9 and he reckoned that it improved his acceleration quite markedly. After the conversion, I did drive his car on a number of occasions and, quite frankly, I did notice only a slight improvement in acceleration - hardly worth the cost involved in doing the conversion. I know, he would disagree with me, but really until one would utilize a stopwatch to check the times, it all becomes a little hazy.

I prefer to go the other way - certainly with a 6.9. The torque is such that the engine will comfortably accommodate the higher gearing, such as you would find in an early 500 differential. I think the ratio is about 2.47:1 as opposed to the 6.9"s 2.65:1. In your case, I do think that the M117 450 engine would cope with the lower/higher (?) ratio - I never know which terminology to use, and if I were you, I would chose the higher gearing. I have a rebuilt 500 differential that, as yet, I have not fitted to Gleaming Beauty. I could be persuaded to part with it. I tend to agree with C107's comments, but am not sure. If I remember correctly, our doctor Bill Babe has gone through this exercise, and you should be able to find it in the Archive section, under Mechanical Repairs. Regards Styria
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Old 4th May 2016, 08:28 PM
aussie 6.9 aussie 6.9 is offline
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Default Re: 450sl diff ratio

Thanks for your reply Styria. Do you know what ratio your diff is, and was it from 500sl 107?
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Old 5th May 2016, 08:22 PM
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Default Re: 450sl diff ratio

Mark, from 500SE or SEL, and I think the ratio is 2.47:1. Will double check for you and, if not correct, will advise you. Regards Styria
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Old 5th May 2016, 08:35 PM
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Default Re: 450sl diff ratio

on the 126 380s were 2.47 or 3.27 depending on year and market
the 500s were 2.24 or 2.82 depending on year/market

These are first generation cars. Not sure about the 107s.
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Old 22nd May 2016, 08:13 PM
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Default Re: 450sl diff ratio

Thanks for your replies members. I now have to decide if having a more relaxed cruising revs is worth the work involved in achieving it. Regards Mark.
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Old 8th May 2019, 07:23 PM
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Default Re: 450sl diff ratio

Still thinking about diff ratios for the 450sl. I have found a U.S. spec sheet which gives the 1978 450sl a diff ratio of 3.46 to 1 which means that at 100k the motor is at 2865rpm. This appears to be the same as my car but I have found another MB tech data book that says the 78 450sl has a ratio of 3.07 to 1 or 2630 rpm at 100k. Can anybody clarify this for me.? Regards Mark
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Old 8th May 2019, 07:37 PM
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Default Re: 450sl diff ratio

It should be 3.06 or 3.07 can't remember which.
It will be printed on the Diff itself.

All the info I have is that the 78 USA 450 is the same as the rest of world, however the 1980 model went to 2.65 for USA
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Old 8th May 2019, 11:13 PM
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Default Re: 450sl diff ratio

Less torque (perfectly normal) slippage with a 450 diff. - the torque converter locks earlier in traffic.
Because of this, fuel economy overall is unaffected.
Less slippage of the torque converter delivers better economy, which is balanced by the engine revving slightly harder for the same speed.

Since the 6.9 was sold to Mark, he has driven it Sydney - Adelaide return 4 times. He never remarked anything about it using more fuel, which one would think would be critical for a car taring at 1,935 kg (more with fuel, two people and luggage for a week away). Also enjoys slightly better acceleration.


As an aside, the 300 SL Gullwing could be ordered with a choice of 4 different diff ratios. The tallest resulted in the fastest road car in the World at the time, the shortest ratio resulted in the best acceleration.
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