SPEED READING

 

You are driving a 30-year-old black-and-white cop car and you are going to get noticed!  So, you may want to obey the speed limit.  With modern tires, a rear-end change or simply a quality control issue, even your “certified” speedometer may be lying to you.  It’s an easy driveway fix.  First, remove your old pinion gear according to the shop manual.  Count the number of teeth and note the color.  Check the chart below and match your existing pinion.

 

                       Pinion Chart

Tooth Count

Part Number

Color

24*

3410024

White

25*

3410025

Blue

26

2538926

Red

27

52068149

White

28

52068150

Blue

29

52068151

Black

30

52068152

Yellow

31

52068153

Green

32

52068154

Black

33

52068155

Yellow

34

52068156

Green

35

52068157

Orange

36

52068158

Red

37

52068159

White

38

52068060

Blue

39

52068061

Green

40

52068062

Orange

41

2538941

Red

42

2538942

White

43

2538943

Blue

45

2538945

Discontinued – Ref. Only

* These pinions require a special adapter, now discontinued.  (P/N 2892994)  All others use 2538608.  Don’t forget new seals – P/N 4883434AA pkg. – 2 seals

 

Take a five mile test drive at an indicated 60 mph using the highway mile markers.  Use a sports stopwatch with 100th second markings. As an example, we made a five mile run in 4.58 minutes.  So, our speedometer registers low, or less than 60 seconds per mile, and we will need a pinion gear with fewer teeth.  We were going faster than the indicated 60 mph.  Simply divide the measured 4.58 minutes by the five miles you drove and you get a factor of .916. Multiply the existing teeth, e.g., 35, by .916 and you get 32.06.  This means we need a 32-tooth pinion, P/N 52068154 for your application.  A factor of more than 1.00 requires a pinion with more teeth.  

 

The adapter that holds the pinion can be installed in one of three positions depending on the number of teeth on the pinion.  It is concentric so as to adapt the varying diameter of the pinions to the number of teeth present.  Replace the seals and follow the book.

 

Thanks to Barry at moparist@bellsouth.net  for his chart and input.