How do you calibrate a GM speedometer?
How do you calibrate a GM speedometer?
GM Speedometer Calibration
- Using Gear/Tire wizard in VCM Editor (Edit> Gear/Tire Wizard) Insert your new tire and gear in the columns on the right.
- When you have entered the correct values for your vehicle click the “Adjust” button.
How do you change the gear on the speedometer?
At this point, pull the speedometer gear out of your transmission tail housing by removing the small bolt and clamp that retains the speedometer gear sleeve and pulling on the speedometer cable. Then count the teeth, subtract or add to the number of teeth and select a new gear from the appropriate chart below based on your transmission.
How does the transmission work on a Chevelle?
The last thing you need to do is install a throttle valve (TV) cable. This connects to the carburetor or throttle body and is how the transmission knows the engine load. The best way to do this is with an aftermarket cable and bracket made for the type of carburetor or fuel-injection system on your Chevelle.
Why does my Chevelle transmission read too high?
Many of you have changed tire size or axle ratio on your Chevelle and now the speedometer reads too high or low. While this can be corrected with an aftermarket ratio adapter, I like to change the speedometer driven gear at the rear of the transmission to correct for error. If you want a “correct” car, this is the way to go.
How many teeth does a transmission speedometer need?
Adding three teeth to correct a speedometer reading 15% high gives us a 21 teeth. We need to buy a 21 tooth (red) 3987921 gear. The GM TH350C, 4-speed and Powerglide transmissions all use the 345215 sleeve but they used three different drive gear diameters, 1.92″, 1.84″ & 1.76″.
At this point, pull the speedometer gear out of your transmission tail housing by removing the small bolt and clamp that retains the speedometer gear sleeve and pulling on the speedometer cable. Then count the teeth, subtract or add to the number of teeth and select a new gear from the appropriate chart below based on your transmission.
Where is the drive gear located on a TCI speedometer?
The accompanying charts show what gears were manufactured for each type transmission. TCI® now stocks the most popular speedometer gears. Note: Drive gear refers to the gear that is on the transmission output shaft. The driven gear is located in a removable housing usually in the tailhousing of the transmission.
Many of you have changed tire size or axle ratio on your Chevelle and now the speedometer reads too high or low. While this can be corrected with an aftermarket ratio adapter, I like to change the speedometer driven gear at the rear of the transmission to correct for error. If you want a “correct” car, this is the way to go.
Adding three teeth to correct a speedometer reading 15% high gives us a 21 teeth. We need to buy a 21 tooth (red) 3987921 gear. The GM TH350C, 4-speed and Powerglide transmissions all use the 345215 sleeve but they used three different drive gear diameters, 1.92″, 1.84″ & 1.76″.
