Speedometer with 18" Wheels
Race Director
Joined: Jun 2000
Posts: 10,046
Likes: 675
From: FL
Wheel size has nothing to do with it. Tire height is the driving factor. 27" tall tires are stock. Also, changing to a different rear end ratio will throw your calibration off.
If the speedometer is off, you may need to replace the speedometer gear where the cable goes into the transmission. Exact gear will be dependent on tire size, rear axle ratio, and type of transmission.
'73 should have a Turbo 400. More info:
https://www.motortrend.com/how-to/ca...-speedometers/
If the speedometer is off, you may need to replace the speedometer gear where the cable goes into the transmission. Exact gear will be dependent on tire size, rear axle ratio, and type of transmission.
'73 should have a Turbo 400. More info:
https://www.motortrend.com/how-to/ca...-speedometers/
Thread Starter
Instructor
Joined: Jun 2021
Posts: 213
Likes: 45
From: Georgia
Wheel size has nothing to do with it. Tire height is the driving factor. 27" tall tires are stock. Also, changing to a different rear end ratio will throw your calibration off.
If the speedometer is off, you may need to replace the speedometer gear where the cable goes into the transmission. Exact gear will be dependent on tire size, rear axle ratio, and type of transmission.
'73 should have a Turbo 400. More info:
https://www.motortrend.com/how-to/ca...-speedometers/
If the speedometer is off, you may need to replace the speedometer gear where the cable goes into the transmission. Exact gear will be dependent on tire size, rear axle ratio, and type of transmission.
'73 should have a Turbo 400. More info:
https://www.motortrend.com/how-to/ca...-speedometers/
Race Director
Joined: Jun 2000
Posts: 10,046
Likes: 675
From: FL
One of the problems is that GM used different drive gears in the transmissions, so choosing the correct driven is dependent on the drive gear.
Suggestion. Pull the speedometer cable from the transmission and ID the current driven gear. If your speedometer reads fast, then you need a gear with more teeth to slow the cable down. If it reads slow, you need less teeth. Get a selection of the gears and try them out. I had to do that with my T-56 Magnum conversion and the perfect gear was actually one tooth less than what the calculator gave me.
https://www.chevyhardcore.com/tech-s...to-correct-it/
Suggestion. Pull the speedometer cable from the transmission and ID the current driven gear. If your speedometer reads fast, then you need a gear with more teeth to slow the cable down. If it reads slow, you need less teeth. Get a selection of the gears and try them out. I had to do that with my T-56 Magnum conversion and the perfect gear was actually one tooth less than what the calculator gave me.
https://www.chevyhardcore.com/tech-s...to-correct-it/
Thread Starter
Instructor
Joined: Jun 2021
Posts: 213
Likes: 45
From: Georgia
One of the problems is that GM used different drive gears in the transmissions, so choosing the correct driven is dependent on the drive gear.
Suggestion. Pull the speedometer cable from the transmission and ID the current driven gear. If your speedometer reads fast, then you need a gear with more teeth to slow the cable down. If it reads slow, you need less teeth. Get a selection of the gears and try them out. I had to do that with my T-56 Magnum conversion and the perfect gear was actually one tooth less than what the calculator gave me.
https://www.chevyhardcore.com/tech-s...to-correct-it/
Suggestion. Pull the speedometer cable from the transmission and ID the current driven gear. If your speedometer reads fast, then you need a gear with more teeth to slow the cable down. If it reads slow, you need less teeth. Get a selection of the gears and try them out. I had to do that with my T-56 Magnum conversion and the perfect gear was actually one tooth less than what the calculator gave me.
https://www.chevyhardcore.com/tech-s...to-correct-it/
