Speedometer gear.
Thread Starter
Cruising
Joined: Oct 2012
Posts: 12
Likes: 1
From: Pittsburgh, PA
Speedometer gear.
Need some help trying to figure what Speedo gear is utilized on a 1969 vette, 350/300hp with a TH400 automatic with a 3.08 rear end.
Might any one know which gear is correct?
Color or tooth count?
Or, Might anyone know of a chart or listing of the Speedo gear applications.
Any assistance is greatly appreciated.
Might any one know which gear is correct?
Color or tooth count?
Or, Might anyone know of a chart or listing of the Speedo gear applications.
Any assistance is greatly appreciated.
Le Mans Master
Joined: Aug 2017
Posts: 8,336
Likes: 2,810
From: Cool Northern Michigan
TCI Automotive transmission has color codes for gears but it's hard to say what color gear is in your tranny now without some disassembly.
There is not a 100% guarantee that you have a 3.08. After decades of ownership, those could have been swapped out. But, easy enough check with both rear tires off the ground.
And of course, tire diameter will change accuracy also.
The "driven gear" is a fairly easy swap. The "drive gear" is a lot more involved, removing driveshaft and tail-shaft housing.
There is not a 100% guarantee that you have a 3.08. After decades of ownership, those could have been swapped out. But, easy enough check with both rear tires off the ground.
And of course, tire diameter will change accuracy also.
The "driven gear" is a fairly easy swap. The "drive gear" is a lot more involved, removing driveshaft and tail-shaft housing.
Race Director
Joined: May 2006
Posts: 18,729
Likes: 2,581
Need some help trying to figure what Speedo gear is utilized on a 1969 vette, 350/300hp with a TH400 automatic with a 3.08 rear end.
Might any one know which gear is correct?
Color or tooth count?
Or, Might anyone know of a chart or listing of the Speedo gear applications.
Any assistance is greatly appreciated.
Might any one know which gear is correct?
Color or tooth count?
Or, Might anyone know of a chart or listing of the Speedo gear applications.
Any assistance is greatly appreciated.
Race Director
Joined: Jan 2007
Posts: 10,682
Likes: 696
From: Danville Illinois
2025 Corvette of the Year Finalist - Modified
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Excellent question.
I am all ears, my 75 has a TB 400 & 3:08 rear, through the years we have had many different sized tires on it, just going by the mile markers on the interstate and our GPS we are close, sometimes higher/lower, next time under the car will check the gear color.
I am all ears, my 75 has a TB 400 & 3:08 rear, through the years we have had many different sized tires on it, just going by the mile markers on the interstate and our GPS we are close, sometimes higher/lower, next time under the car will check the gear color.
Race Director
Joined: May 2006
Posts: 18,729
Likes: 2,581
Excellent question.
I am all ears, my 75 has a TB 400 & 3:08 rear, through the years we have had many different sized tires on it, just going by the mile markers on the interstate and our GPS we are close, sometimes higher/lower, next time under the car will check the gear color.
I am all ears, my 75 has a TB 400 & 3:08 rear, through the years we have had many different sized tires on it, just going by the mile markers on the interstate and our GPS we are close, sometimes higher/lower, next time under the car will check the gear color.
Thread Starter
Cruising
Joined: Oct 2012
Posts: 12
Likes: 1
From: Pittsburgh, PA
Thanks to all for all the help. To my best understanding my driven gear was supposed to be the dark green 42 tooth.
As I just recently rebuilt the Diff and confirmed it is definitely a 3.08.
The car was a basket cast project. Nearly completed now when I sprung a significant leak from the Speedo housing. It was obvious upon removal that someone had botched an attempted repair previously. What I pulled out was a yellow 41 tooth. I always felt the speedometer was a little off.
Could not find documentation to confirm the correct gear.
Thank again for the confirmation.
As I just recently rebuilt the Diff and confirmed it is definitely a 3.08.
The car was a basket cast project. Nearly completed now when I sprung a significant leak from the Speedo housing. It was obvious upon removal that someone had botched an attempted repair previously. What I pulled out was a yellow 41 tooth. I always felt the speedometer was a little off.
Could not find documentation to confirm the correct gear.
Thank again for the confirmation.
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Racer
Joined: Nov 2017
Posts: 319
Likes: 125
From: Midwest
When I bought my `79 some 13 years ago, I noticed the speedometer was indicating about 10 mph too fast at 50 mph actual vehicle speed.
For what it`s worth, in my own C3 experience with these speedometer gears, I observed that an increase in the number of teeth reduced the indicated speedometer reading relative to actual vehice speed at the rate of about 3-4 mph per added tooth at 50 mph actual vehicle speed.
For what it`s worth, in my own C3 experience with these speedometer gears, I observed that an increase in the number of teeth reduced the indicated speedometer reading relative to actual vehice speed at the rate of about 3-4 mph per added tooth at 50 mph actual vehicle speed.
