In my 70 Buick skylark 350 I just had a posi unit with 3:73 gears installed. I have two questions. My speedometer is now off and was wondering what speedometer gear I need to install to correct this problem. Any suggestions? Also I noticed the TH350 shifts fast and the passing gear kicks out quickly as well. Should I be concerned and can this be corrected? Thanks!
3:73 gear are high for a turbo 350, your rpms are going to be really high at highway speeds, and gas mileage will suck. Check online for a calculator, you have to put in tire size and some other information. 3:73 gear are great if you have an overdrive, I have them on my 69 Skylark w/200r4 transmission
To correct your speedometer, you need 3 numbers, 1) your rear tire size. 2) Gear ratio (3.73) 3) the number of teeth on the speedometer DRIVE gear. The DRIVE gear is on the output shaft of the transmission. To see it, you must remove the DRIVEN gear sleeve. It is a helical gear. With the transmission in neutral, and the rear tires off the ground, you can turn the drive shaft slowly and count the teeth. With hose 3 numbers, you can figure out what DRIVEN gear you need to correct the speedometer. Sometimes it is necessary to change the DRIVE gear as well.
Like above You need to know your tire height and what drive/driven gears you have. You can use the calculator I am linking below to determine: https://www.tciauto.com/speedometer-gear-calculator
Jaye this car is rarely driven on the highway. I failed to mention it has a 9.5 inch torque converter with 2500 stall. Not sure if that makes a difference. It has 14 inch tires.
Doesn't make any difference at all, but unless you have the 3 numbers I referenced, no one can help you. Need the actual TIRE size so we can figure out the tire height. Then you have to do the work of pulling out the sleeve to count the teeth on the DRIVE gear.
