Hi all,
I finally fitted the speedo gears in the Getrag 265 and the speedo now works, but indicates a much lower speed than the real one. I first thought of having my speedo recalibrated but I then realized the odometer would not show the correct mileage. So the easiest way would be to fit a ratio adapter like this one:
http://www.ebay.com/itm/Gear-Ratio-Adapter-to-speed-your-Speedometer-up-61-/130470751572?_trksid=p2054897.l4276
For this, I need to determine the ratio I need. Below are some calculations:
- Original tires: 185R15; current tires: 205/70-14; speed reads faster by + 2.5% as per this website:
http://www.tacomaworld.com/forum/tirecalc.php?tires=185-82r14-205-70r14- Original MB transmission "Wegstreckenzahl" (whatever that means) is 869 or 892 while the Getrag one is 756, according to this post:
http://www.sl113.org/forums/index.php?topic=16893.msg121239#msg121239 so speedo reads slower by [(869 - 756)/869]x100= 13%, or 15% with the 892 figure. Here it would be nice to understand why this difference between the theoretical and "real" Wegstreckenzahl
- Original rear end ratio: 3.92:1; current rear end ratio: 2.82:1; speed reads slower by [(3.92-2.82)/3.92]x100=28%
So, assuming I'm driving at 100mph, tire difference would have the speedo read 102.5mph. From there rear end ratio difference would have the speedo read (102.5/3.92)x2.82= 73.74 mph; from there the Wegstreckenzaht difference would have the speedo read (73.74/892)x756= 62.5 mph, or 64.15 mph with the 869 figure.
Now, interestingly, 100 km are 62.14 miles. So, if I'm not wrong in my calculations, I could just fit a km speedo that was fitted with a 3.92 rear end and read the correct speed in mph. A speedo in km out of a car fitted with a 4.08 rear end would have me read 64.7 mph instead of 100 kmh. However km speedos are graduated up to 220kmh, so the useable range would be quite limited on the dial.
The other solution is to fit a speedo adapter that converts from mph into kmh, as the one mentioned at the beginning of my post. But I need to make sure thread diameter and pitch of the adapter matches the one of the MB speedo.
So, please, let me know if my calculations are correct. If you have any experience with a ratio adapter, I'm also interested in your experience, especially regarding thread diameter and pitch.
Thanks a lot in advance for the help!
