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  #1  
Old 05-13-2012, 04:08 PM
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Whose axles did I put in my 300SDL?

So about 2 years ago I was reading through all the info on differential swapping to get a better gear ratio. It all seemed to make sense to me so I went out to the junkyard looking for a good candidate differential for my 300SDL. After a bit of a search I found a 3.07 diff and axles to replace my 2.88. Long story short I love the swap, the car drives better, responds better, and shifts better.

Unfortunately I neglected to write down what model my new diff came out of for future reference. Now, two years on, one of the axle boots has ripped from age and I'd like to replace the axle, but I don't know what axle it is...
The axles fit the SDL but are somewhat different.
Some characteristics of the new axles:
  • Larger diameter near differential then SDL axles
  • Allen bolts, not triple squares like SDL axles
  • Exterior bolts to diff. not internal clip
I'd really like to replace the axles if anyone can help me figure out what model my axle/diff combo came from. Any help is much appreciated.

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Old 05-13-2012, 05:52 PM
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You have the larger sized diff that was available on the V8's of that era. If you check, you'll probably find that the screws that secure the bolt flange are 12 mm and not the 10mm screws that the SDL originally had.

What's curious to me is the claimed ratio of 3.07. AFAIK, all the gassers of that era, with the exception of the 300SE, had the 2.47 diff. The SE had the 3.46 diff.

If the diff is what I believe it is, any axle that came from one of the V-8's would work.

BTW, the bolts on the outside of the housing don't secure the axle or the stub shaft. There are still internal clips for that task.
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Old 05-13-2012, 06:28 PM
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Does the SDL normally have clips to mount the axles? I had replaced the axles once before the swap and did so by removing the six triple square bolts. Was that the incorrect way to remove them?

Also, I thought about it again and you're right, it was a 2.47. I forgot which direction I had changed it (Higher ratio vs. lower ratio). After some thinking I remembered that I had gone with a lower ratio for lower engine speeds so it must be a 2.47.
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Old 05-13-2012, 08:09 PM
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Isn't a 2.47 in place of a 2.88 technically a higher ratio? More wheel rpms per input rpm.

Sixto
87 300D
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Old 05-13-2012, 09:36 PM
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That may be the correct way to look at it, frankly I'm not sure. My brain was just thinking that 2.47 is lower then 2.88.
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Old 05-13-2012, 10:43 PM
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Quote:
Originally Posted by sixto View Post
Isn't a 2.47 in place of a 2.88 technically a higher ratio? More wheel rpms per input rpm.

Sixto
87 300D
Lower ratio I think as it takes fewer turns of the driveshaft to turn the axels with the 2.47. Somewhat confusing I admit at times and always think it over for a second before posting.

Gear ratios are usually expessed from the input of power point perspective. I would think the 2.88 is a higher or greater ratio than the 2.47.
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Old 05-13-2012, 10:45 PM
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lower ratio equals a larger number in the ratio to 1
higher ratio equals a lower number in the ratio to 1
tall gearing equals high ratio
short gearing equals low ratio
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Old 05-13-2012, 10:53 PM
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Quote:
Originally Posted by vstech View Post
lower ratio equals a larger number in the ratio to 1
higher ratio equals a lower number in the ratio to 1
tall gearing equals high ratio
short gearing equals low ratio
I freely admit I am not sure as there might be several interpretations out there as well. I do not think it is unusual to see a little confusion in this area even though the principals are well understood. Logically if it takes more turns it should be a higher ratio. Fewer a lower ratio.

Again this is subject to corrrection. I have seen what I thought was wrong as well as right too many times to be certain.
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Old 05-13-2012, 11:06 PM
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lower ratio means easier to move. as in 1st gear is around 3:1 ratio 2nd gear is around 2:1 3rd gear is around 1.5 : 1 and 4th gear is usually 1:1 higher gears require less engine rpm to each wheel rpm...

taller is generally the term used in diff gearing, and it's synonymous with higher. as in the engine feels like it's climbing a taller hill with a tall gear in the diff.

I agree there is a lot of confusion on terminology... but confusion does not mean it's right.
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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!
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  #10  
Old 05-13-2012, 11:53 PM
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Quote:
Originally Posted by djustin973 View Post
Does the SDL normally have clips to mount the axles? I had replaced the axles once before the swap and did so by removing the six triple square bolts. Was that the incorrect way to remove them?

Also, I thought about it again and you're right, it was a 2.47. I forgot which direction I had changed it (Higher ratio vs. lower ratio). After some thinking I remembered that I had gone with a lower ratio for lower engine speeds so it must be a 2.47.
Yes, they all have clips.

Your procedure was fine. Those bolts connect the outer axle and shaft to the hub. The replacements are sold that way so you don't need to remove the hub.

However, if you ever want to remove the hub, you'd need to go inside the housing and pull the clips.

A "lower numerical ratio" equates to a "taller ratio." You're guaranteed to cause confusion when you refer to "higher ratio" or "lower ratio". These terms can be interpreted either way.

In any case, you almost certainly have the diff from a 420 SEL. The axles from the 560 SEL would also be suitable.

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