I recently swapped my original 1992 firebird (305 TBI & 5 spd) cluster, with 120 speedo and 6 grand tach, for one with a 140 speedo and 8 grand tach. I also had to take the 140 speedo apart so I could reset the odometer to my original speedo's mileage (that was a treat, only took 3.5 HOURS to get everything lined up to read right!!). All of the gages work fine except that how the speedo reads 2-5 mph slow, when compared to my GPS unit. speedo 20 is really 22, 30 is 35, 40 is 45, 50 is 55, 60 is 63, 70 is 73, 80 is 83, 90 is 92, too much traffic to go the rest of the way...This is an electronic speedo and does not have a cable, so I assume there is no gear in the trans to change like with a cable. Would the speed sensor have to be changed? I am still learning the site as I am not on that often. I tried to looked through the FAQ section with no luck. Oh, I also had to pull the speedo needle off to get access to the odometer, could that be an issue? I was careful to note where the orientation of needle and shaft and put it all back in the same position with the needle next to the trip meter reset shaft. Any Ideas?

 

Hi
there are 2 gears in your tranny.

1 On the shaft
and
1 on the end of the speed unit (the thing with the plug on it)
in your tail shaft.

cant think of the name of the place you can get your gears from.
you can do a search. it's on this site some place.

you can fix it your self. parts run about $14 a gear most of the time with your speedo that close it just takes one gear.. all that info is on the tranny site..