24 Turtle??

[38convsedan]

My 38 CS has a 4.11 rear end (stamped 9 37). I believe it should have a 21 tooth speedometer gear in the turtle. Speedometer reads significantly below actual MPH.

I believe correct turtle should be stamped 3 37. Mine is stamped 24 (see photo).

Is the current 24 turtle mean it has a 24 tooth gear?

As always, thank you in advance for your help!

Steve

[petehoovie]

Originally Posted by 38convsedan

My 38 CS has a 4.11 rear end (stamped 9 37). I believe it should have a 21 tooth speedometer gear in the turtle. Speedometer reads significantly below actual MPH.

I believe correct turtle should be stamped 3 37. My is stamped 24 (see photo).

Is the current 24 turtle mean it has a 24 tooth gear?

As always, thank you in advance for your help!

Steve

[deuce lover]

Yes 24 tooth gear.

[Kube]

A 24-tooth driven gear is typically for a 4:55 differential.
If you truly have the 4:11, you need the 21-tooth driven gear.
As installed at the factory, it will have a "21" cast upon the housing.
This is based on the assumption you have 6:00 x 16" tires.

[38convsedan]

Kube, yes-6.00 x 16 tires.

Does this 24 tooth turtle explain speedometer inaccuracy??

Are 21 tooth turtles available?

[V8COOPMAN]

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Originally Posted by 38convsedan

Kube, yes-6.00 x 16 tires.

Does this 24 tooth turtle explain speedometer inaccuracy??

Are 21 tooth turtles available?

Here's a hard-to-find chart with the numbered turtles and their usual applications.

Coop




.

[38convsedan]

Thanks for the chart!
I don’t see a scenario for 24 tooth turtle with 6.00 x 16 tires….

[V8COOPMAN]

Originally Posted by 38convsedan

Thanks for the chart!
I don’t see a scenario for 24 tooth turtle with 6.00 x 16 tires….

That is likely why your speedometer error exists. I only see two instances on the chart where a #24 turtle is used in conjunction with a 16" tire. Both of those are shod with 5.50 X 16 tires and obviously are fitted with a 4.55 rear end. I'm going to guess that those two combinations were likely 1939-1940 V8-60 powered pick-up trucks, as we know that V8-60 powered vehicles use 16 X 3.5" wheels, and those wheels were considered too narrow for 6.00 X 16 tires. 1940 was the last of the V8-60 engines. #21 turtles are among the most-common.

There is a third instance on the chart where a 24 turtle is used, but you'll note that the tire size is a 6.50 on a 15" (fifteen-inch) wheel, probably on a 1947 or '48 farm pick-up with a 4.55 rear gear.

Coop


.

[38convsedan]

Ok…found three on eBay.
Two seem to be oriented differently my current one, with threaded speedometer cable end facing up relative to stamped 21.
The third turtle marked 9 3 and 21 is oriented as the current turtle on the car, with threaded cable end facing down relative to stamping.
Which to buy??

[Kube]

Originally Posted by 38convsedan

Ok…found three on eBay.
Two seem to be oriented differently my current one, with threaded speedometer cable end facing up relative to stamped 21.
The third turtle marked 9 3 and 21 is oriented as the current turtle on the car, with threaded cable end facing down relative to stamping.
Which to buy??

Any of the three should suit your purpose.
Me? I prefer the best I can get. In this case, the NOS. It is pricey though.

[Terry,OH]

Yes any of the three.

[38convsedan]

Thanks guys!