How do i correct my speedometer?

im about to change gears in my 96 chevrolet blazer s10 4x4. i am currently running 3.08's on 31'; tires. i want to go to 3.73's in the front and rear(nothing wild). my speedo is off about 6-7 mph as of now so i know it'll be more after changing the gears. what do i need to do to get the speedo to read correctly with the new setup?How do i correct my speedometer?
hi there!



That speedometer is driven using an electronic sender in the transmission.



The speed signal is then run thru a computer/ecu or a buffer.



The speed signal then goes to the speedometer to run it.



You MUST change the signal at the computer.



This could be easy or complicated.



Call 1 800 442 4491. this is Speedo-tach in Concord California.



Ask for Kris Genter.



He can more than likely calibrate your vehicle by sending you a drac/ecu with the correct ratio for your vehicle!



Usually costs about $100.



I have calibrated Many Many Chevys this way.



I hope this Helps!



Good Luck!How do i correct my speedometer?
Mm not sure on the steps to take, but I know you can take it somewhere and get it calibrated.
I know every thing went to OBDII in 96, so you might be able to get a programmer and adjust it that way.
Pull the speedometer driven gear out of your transmission

count the number of teeth on the drive gear

use the following formula to determine the number of teeth needed on the driven gear

# of teeth needed on driven gear=# teeth on drive gear*axle ratio*tire Revelations per mile/1001

Tire Revelations per mile=20168/tire diameter in inches

If you can't get a driven gear with the proper number of teeth on it you may need to remove the tail housing from the trans and replace the drive gear then start all over again
After rear end swap. Use a GPS unite and drive vehicle. This will tell your actual speed and you can see how far the speedo is actually off. You can go to a GM Dealer parts department and they should be able to tell you what gears would be used in that combination. Your other choice if the speedo isn't off by to much. Is count the teeth on the driven gear and adding i tooth is = to 5 mph. You'll need to know if your speedo housing is a small bullet type or the bigger round one . Also take your vin to the parts department, they may need the last 8 of the vin. Hope this helps
Change out your transmission speed odometer gear.From the dealer purchase the GREEN gear for your purpose.