i have a 92 rs that i swapped the rearend from 2.73s to 3.42s typical since i have a 700r4 and 245/50r16 tires but from my research here i found i needed a 40 tooth driven gear.maybe im not sure which gear it is exactley but the one that goes on the speed sensor its self. well before this my speedometer was working intermittently so i figured good time to put a new sensor in so i go to advance auto and get the sensor for my car put it in with the 40 tooth gear and according to the gps i need to go 70 on my speedo to go 60 on the gps so i tried a 41 tooth gear and same result does anyone have any input as to why my speedo is still reading off by 10 mph over with the correct gear?

 

It takes two gears, the driven gear and the drive gear. One goes in the speedo housing on the side of the tranny, the other goes inside the tranny on the shaft.

 

Probably because 41 isn't the right gear.

There is a sticky thread in this forum with speedo gear info and a lot of it conflicts with the gears GM used in production vehicles.

Not a big deal; you have 42, 43 and 44 to try.

 

This first batch is for anyone using a 700R-4 with any of these tire
sizes on the rear axle of their car:
205/60R15
225/55R16
245/50R16
245/45R17
275/40R17
315/35R17
245/40R18
If your tire size isn't here, don't use these results.
2.73:1 use 41 tooth driven with 19 tooth drive
2.77:1 39 18
2.86:1 38 17
2.93:1 39 17
3.00:1 40 17
3.07:1 41 17
3.07:1 36 15
3.08:1 41 17
3.08:1 36 15
3.23:1 38 15
3.23:1 43 17
3.25:1 38 15
3.27:1 44 17
3.31:1 44 17
3.31:1 39 15
3.42:1 40 15
3.45:1 41 15
3.50:1 41 15
3.54:1 42 15
3.55:1 42 15
3.70:1 44 15
3.73:1 44 15
more no cal.

thanks to atilla this list shows what speedo gears you know for what rear end gears it shows 3.42 takes a 40 tooth driven and a 15 tooth drive which is what i have though even tryed the 41 and its still off

 

have you ran a timed mile? 60mph constant from mile post to mile post on the highway? use that to check Both your speedo and the mph reading on the GPS. My gps does the same thing by about 5mph.

 

Thanks for what? 41 isn't correct.
245/50R16 is significantly shorter than the 215/65R15 tire that used a 15drive/41driven with 3.42 / 700-R4.
Usually, comparing diameter or rev/mi. of different tire sizes vs. the GM charts will put you right on what's needed. But anymore, there's barely any models of tires made in those old early 80s stock sizes on the charts.

Bottom line? You'll need a 42 or 43. And the info in the sticky is again wrong.

 

ok jmd i apologize and thank you.i didn't understand what you were saying and i now do again thanks for the help