Double Six
Active Member
Does anybody know which speedo gear(how many teeth) would go on 67 barracuda, came with 273 4bbl. 71/4. Sorry, I don't know what gear ratio. Thanks, Double Six.:???: [/B]
904 speedo gear
- Thread starter Double Six
- Start date
-
AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
- Joined
- Jan 19, 2014
- Messages
- 25,838
- Reaction score
- 13,144
Double 6, What color am I thinking of?
My 69 Service manual lists about 100 or more combinations of tire size and gear ratios, to select gears with teeth ranging from 26 to 41. Thats 16 different gears. But because Im such a nice guy, Ill offer 29 to 33.That narrows it down to 5 possibilities. One of those will get you into the ballpark. Then, the percent mph error is the percent change required in tooth count. If the read-out needs to increase, the tooth count will need to decrease, and viceaversa.
Even if you knew the rear ratio theres still a 2 or 3 gear possibility.And even if you knew both the ratio and the tire size, there could still be a 1 or 2 gear possibility. Thats because the chart is set up with bias ply tire sizing, and I dont have a cross reference from bias-ply to Pmetric.
So thats the best I can do.Stick a 29 or 30 or 31 tooth in there and go calibrate it. Then fine tune it.
My 69 Service manual lists about 100 or more combinations of tire size and gear ratios, to select gears with teeth ranging from 26 to 41. Thats 16 different gears. But because Im such a nice guy, Ill offer 29 to 33.That narrows it down to 5 possibilities. One of those will get you into the ballpark. Then, the percent mph error is the percent change required in tooth count. If the read-out needs to increase, the tooth count will need to decrease, and viceaversa.
Even if you knew the rear ratio theres still a 2 or 3 gear possibility.And even if you knew both the ratio and the tire size, there could still be a 1 or 2 gear possibility. Thats because the chart is set up with bias ply tire sizing, and I dont have a cross reference from bias-ply to Pmetric.
So thats the best I can do.Stick a 29 or 30 or 31 tooth in there and go calibrate it. Then fine tune it.
Double Six
Active Member
Thanks, AJ/FormS The trans I bought was missing that and I had no idea where to start. The wit trans web page had a whole page of different gears like you said. Thanks, again.
You will need to know the rear gear ratio and tire height, to get the correct gear.
I'd go with AJ, and put in the 30 to start, then work from there! When all is equal, it should correspond with your gear ratio, and so assuming you have a 2:94 through a 3:21, 30 should be close!
AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
- Joined
- Jan 19, 2014
- Messages
- 25,838
- Reaction score
- 13,144
Nice chart
I upgraded my chart to match. button pushed.
Years ago I committed a formula, that I had worked out, to memory.It basically worked out that at 26.5 inch tire, the toothcount equalled the gear ratio,minus the decimal. Then you adjusted for tire size using percents. So a 2.76 used a 28 tooth, and a 3.91 used a 39 tooth, etc. If your tire was smaller, say 5% or 25.2", you would add 5%teeth, or the 28 becomes 29.4, and the 39 becomes 41. You get the idea. The chart was history.
I upgraded my chart to match. button pushed.
Years ago I committed a formula, that I had worked out, to memory.It basically worked out that at 26.5 inch tire, the toothcount equalled the gear ratio,minus the decimal. Then you adjusted for tire size using percents. So a 2.76 used a 28 tooth, and a 3.91 used a 39 tooth, etc. If your tire was smaller, say 5% or 25.2", you would add 5%teeth, or the 28 becomes 29.4, and the 39 becomes 41. You get the idea. The chart was history.
-
