Speedometer marking?

[E60coyote]

My speedometer is off over 15mph at highway speeds. I have a ‘76 with a 3.90 diff (confirmed because I just resealed it).  So I expected to see W=1.39 on the back of the speedometer but I do not. Can anyone tell me what I have based on the picture?  Is there another way to verify the speedometer?

[Conserv]

Your speedometer was manufactured September 1988 (“9.88”). Assuming it is a replacement ‘02 speedometer, and not from a different model of BMW, I don’t see any “W=1.xxx” designation. So it could well be for a 3.64, or other, differential ratio.

And even if you see a “W=1.xxx” number, you can’t always trust them. In 1976, BMW put 3.64 gearing in a large number of speedometers marked W=1.393. My ‘76, which I bought new, was one of them, and I didn’t realize I had a 10% speedometer era until the GPS era!

 

You can either have a firm such as North Hollywood Speedometer calibrate this speedometer, or you can find a speedometer with more appropriate gearing.

Below is my ‘76’s original speedometer, manufactured March 1976 [“3.76”] and marked W=1.393 — but carrying gearing for a 3.64 differential. Following that are two notes regarding the issue, appearing in the September and October 1976 Roundel.

 

Regards,

 

Steve

 

Edited May 27, 2020 by Conserv

[E60coyote]

Ugh.  Thanks!  So much for original miles I guess..  so the fix is either replace with the w=1.39 or have mine recalibrated...

[Son of Marty]

First step, have a speedo shop determine what ratio it is now.