'76 DeVille Speedometer Gear

[mgbeda]

Hi again,

Background: Ol' Bessie has had a 2.93 rear end since the early 80's (a used replacement for the original 2.73).  I intend to keep that since it really makes a difference in the pick-up (I've owned four '76 DeVilles over the years, so I know).  But it would be nice if the speedometer read about right instead of about 10% high, which it has all these years.

Question:  There's a speedometer gear on ebay  BLUE, 38 TEETH, 2.93-1. PART # 1600538 GROUP # 4.337

Is this all I need to change to make the speedometer and rear axle agree, or will I need to change the whole gear set?

Thanks,

-mB

[Dave Shepherd]

That will work, are your tires close to the same circumference as oe, this will affect speedo readings also.

[bcroe]

You can look up the recommended gears, and probably get near as
accurate as factory.  To get it dead on the first time, MEASURE just
how far off your speedo & odometer are (hopefully, both the same
amount).  Then peek inside the trans and see what gears are in
there now. 

Calculate the ratio of the present gears, and multiply by the error
to get the ratio you really want.  If the driven gear were 37 teeth
and you read 110% of true, 37 times 110% says 39.6 teeth will
put you right on.  Practically, a 39 or a 40 tooth will be close.  By
changing both the drive and driven, you might be able to get closer. 

Generally driven gears are 34 to 45 teeth; 2 different housings are
marked for 34-39, and 40-45.  The drive gear could be 15-20 teeth. 

If the odometer and speedo cant agree, the speedometer head needs
some work.  good luck, Bruce Roe

[mgbeda]

Thanks guys,

What I was really asking was whether you can change only the driven gear or if the driven and drive gear have to match.  If I can change only the driven gear this ebay one will save me a trip to the junkyard; if both have to be changed at the same time then I might as well get both at the junkyard.

Testing it is not an option as Bessie is currently in a million (carefully labeled) pieces in the barn and two sheds.  But I do recall that the odometer was off the same amount as the speedo.

-mB