when did the spedometer change
 

When did the speedometer change from 85 max speed to 125?

300SD

With the 2.88 rear end. '85 or better.

Actually it was changed for the 1983 model year includes the 3.07 ratio diff.

Yep, our '83 300D has a 125mph speedo....my dad's car has a 160mph though. :D It was swapped in when the car was brought over from canada in 1989. :)

Mine has the legendary 85mph speedo, I like it because of the big spaces between each 5mph, lets you be more precise/don't have to look at it so close.

55 mph speedometers
The law was Federal Motor Vehicle Safety Standard 127,
a NHTSA regulation. The repeal process started shortly
after Reagan took office. The Federal Register notice
stated:

In February and March of [1981], NHTSA undertook a
comprehensive review of its existing and pending
vehicle safety standards. The purpose of the review
was to determine what modifications could be made to
the standards to reduce the regulatory burden on the
automobile industry without sacrificing safety. Among
the factors considered in evaluating each standard was
the magnitude of the standard's contribution to
safety, the likelihood that manufacturers might
continue to comply with the standard after its
modification or rescission, and the costs of the
standard. ...

Among the standards considered was Safety Standard
No. 127, Speedometers and Odometers (49 CFR 571.127).
... The speedometer requirements became effective on
September 1, 1979.

The rule was officially revoked effective March 25, 1982.

My 82 wagon has a 125mph speedo, and my manual 240 has a 100mph speedo.

Really? What's the month your TD was manufactured? Also, what is the part number on the face of your speedo and do you have the center silver buttons?

The 240 was built before 1980, so it should have the 100 mph speedo.

The wagon was built in 10/81. And the part number is 123 542 18 57.

That is the speedo that is found on the '83 300D, CD and TD. You have the black center buttons, it is my belief your speedo is not original.

It does have a black center button. While the other two are silver. Where are you finding the info on which speedos go with which car.

Side note. The car fax on the car when I bought it didn't show any odd milage stuff so I wonder if someone put in a different one that was at least close to the original miles.

From my memory :D through research on the net and boneyards.

1983 - 123 542 18 57
1984 - 123 542 28 57
1985 - 123 542 27 57

Except I don't remember the '82 and earlier 300 series part numbers, but definitely the '82 speedo should have the center silver button and 85 mph. The PO might of wanted a 125 mph instead of the 85 mph.

If it should have an 85 mpg speedo my speedo and odometer would be read incorrectly wouldn't they? They are both a off just a tiny bit, but nothing out of the ordinary. Maybe a mile or two off at 65, and a few tenths off in 100 miles

No not really. It would be very close but not exact. You have 3.07 diff. and the '82-84 speedos should be very close to each other. The '85 has the 2.88, now that would be off a bit more.

Seems to me that they would be quite a bit different since the sweep of the needle is the same on both speedos but the numbers are in different places.