Decrease rpm's

[HugoVervliet]

For a long time we have a '65 Pagode 230 SL automatic clutch
We now are retired and do a lot of mileage, couple weeks ago we just made a trip of 3,000 miles which brought us through 9 different countries
Wondering if it is possible to bring the RPM's down by changing the back axle.  We now have a back axle of a 280 SL, at 4500 RPM the speedo reads 80 MPH and the car makes a lot of noise
It would be ideal to be able to bring the RPM down for about 1000 RPM
which possibly might reduce the fuel consumption as well
thanks beforehand for all ideas and reactions

[Naj ✝︎]

Hello, Hugo,

Welcome to the Group.

There are lots of discussions on the back axle. You can use the 'search'  function on the top right corner of the screen to find these using search term 'back axle' or 'rear axle'.

Your 230 probably came with a 3.75 axle. If you fitted the 280 axle complete, it can be a 4.08, or 3.92.

In Europe you can find an axle from a 280SE 3.5 which could be 3.69 or 3.46 ratio. The 3.46 has a bigger diff casing and an oil cooler tube. David Brough's post has details of problems he encountered with the cooling tube. In the US, a 3.27 or 3.23 ratios were also used.

http://index.php?topic=8490

Hope this helps.

naj

[graphic66]

The cars were designed to run at these RPM's. That is where they develop the best power and performance. Peak torque and horsepower are 5000RPM and above. If you want a sluggish car that revs like an American V8 change the axle. If you want a great performing little gem as designed by some of the best automotive engineers at the time, rev the car up and enjoy. You very well could have a 4:08 axle in the 230, many were sold like  that. They start out in second gear. A higher rearend ratio will have a hard time starting on hills in second. You will learn to love the sound of the car reving like it was meant to do.

[hill]

quote:Originally posted by graphic66

The cars were designed to run at these RPM's. That is where they develop the best power and performance. Peak torque and horsepower are 5000RPM and above. If you want a sluggish car that revs like an American V8 change the axle. If you want a great performing little gem as designed by some of the best automotive engineers at the time, rev the car up and enjoy. You very well could have a 4:08 axle in the 230, many were sold like  that. They start out in second gear. A higher rearend ratio will have a hard time starting on hills in second. You will learn to love the sound of the car reving like it was meant to do.

A  properly tuned transmision will start out in first gear, you just apply a little more pedal.

[paulr]

swapping the axle on my car (280) to a 3.69 was the single best thing I have done. The car is smooth, very torquey in the middle, and nicely behaved in traffic. All this low end grunt worry does not apply to our cars in my opinion. Occasionally I have to manually put it into 3 going up a hill but so what? Do it, you will so pleased you did. I do a lot of miles in mine and now the car is as I always hoped it could be.

 

quote:Originally posted by HugoVervliet

For a long time we have a '65 Pagode 230 SL automatic clutch
We now are retired and do a lot of mileage, couple weeks ago we just made a trip of 3,000 miles which brought us through 9 different countries
Wondering if it is possible to bring the RPM's down by changing the back axle.  We now have a back axle of a 280 SL, at 4500 RPM the speedo reads 80 MPH and the car makes a lot of noise
It would be ideal to be able to bring the RPM down for about 1000 RPM
which possibly might reduce the fuel consumption as well
thanks beforehand for all ideas and reactions

[Garry]

I agree with Paul.
 I have just got my car back last week after changing from 4.08 to a 3.46 diff and it is fantastic for open highway running and when I want to be the boy racer then I just find some winding road and drop it down a gear or three.  I should have done it five years ago instead of waiting to see if I could find a decent 5 speed gearbox.

As Jeremy Clarkson said on Top Gear, put the foot down on the auto and it just makes a bit more noise but not much action.

http://au.youtube.com/watch?v=ETze4VpDS1g&feature=related

 That aside, for open road, that lower top gear makes the car so much more comfortable.

[HugoVervliet]

thank you all for reacting this quickly to my question. The solution I understand will be to install a back axle of a 280 SE
Yes, it is true that driving the car as it was designed it really is a joy, however as you all know especially in Europe the fuel and the lpg (autogas) are very expensive
Yes, yes the car drives on lpg allowing us a lot more joy out of driving it a whole lot more for the same amount of money as regular fuel
for instance lpg is 0.51 eurocent whereas fuel here is 1.45 euro/liter and higher
also with lpg you do not loose a lot of hp, it runs great!

[66andBlue]

Wow, where did you find a 3.46 rear axle? In California??

[Garry]

Trev,

I have full confidence you will not regret it.  I suspect the lower diff (3.27) is too low especially for the manual as I believe the 3.46 keeps my revs in the sweet spot in both 3rd and 4th in my 4 speed for our local speed limits eg 80kph (50mph) and 100kph (62mph)
Interested in your comments after drive.