Help with speedo gear

[Vanspeed]

The speedo cap that was on my 35 rear was a for a 4:11 gear. I thought maybe I could use it but it does not match my rear end. My axle I am using is a 39 3:78. Does anybody have used ones for sale? Any vendors? Looked on the usual sites and didn't find much.

[flat-v8]

I'm pretty sure I have one #19 I'll sell fairly cheap bought awhile back, I'll never need it. I'll have to find it first!

[Mac VP]

We have a few in different sizes. If Flat V8 can't come up with one check back with us. We don't list those on our website because I have such a limited supply and never know when or if I could find more.

[Vanspeed]

I got a pm from a guy saying he would trade his 19 tooth cap for a 20 but when I count mine it is 21? I feel 21 is the correct number for a 4:11? I see no mention of 20 tooth gears.

[RobR'35]

Is there an ID designation for what drive shaft driver gear
goes with what driven gear for the speedometer cable per whatever the diff. is geared for?
3:25
3:50
3:78
4:11

[flatheadfan]

Sponsored Links (Register now to hide all advertisements)

If I understand what you are asking, the enclosed chart should answer your question. As an example, gear number for a 4.11 rear axle '35-'36 is 68- 17270-A. It has a "20" which is stamped on the "turtle" case. When determining what speedo turtle should be used it gets somewhat complicated when non-standard tires are used. As for the 3.25, I don't believe Ford made such a ratio at the factory for passenger cars. I could be very wrong on this but I believe some applications on Model A commercial vehicles used a "17" which may be appropriate for a 3.25 rear axle. Unfortunately, the "17" turtle is hard to find.

Tom

[Adam/Mill Valley CA]

Bratton's model A parts catalog has new 17,18 and 19 tooth gears that fit the v-8 turtle

Adam

[RobR'35]

That's a great chart!
Is there a chart like that for the "Driver" gear?
The one that goes on the drive shaft.

[deuce lover]

Originally Posted by RobR'35

That's a great chart!
Is there a chart like that for the "Driver" gear?
The one that goes on the drive shaft.

I believe that that driveshaft gear is the same for all.In a 34 I had yrs ago it had 4.11 and I changed them out to 3.54,kept the same driveshaft gear.No problems.

[flatheadfan]

I agree with Deuce. The spiral gear on the driveshaft is the same.

[RobR'35]

Does anyone have the tooth count on the driver gear for the drive shaft?

[26 lakes]

I have a dozen driver gears and they are all the same. There were 3.54, 3.78 and 4.11 rear end gears.

[JSeery]

Originally Posted by RobR'35

That's a great chart!
Is there a chart like that for the "Driver" gear?
The one that goes on the drive shaft.

The chart is out of the Green Book. The book has LOTS of information, not sure how people get by without using it!!!

[Rowdy]

Don't forget the 4.44 gears. Those used a 23 tooth drive gear. Rod

[RobR'35]

My mistake. I mean the gear count on the driver gear on the drive shaft for the speedometer.
As to the green book. I've so many other great books but not the green one.
Looks like it's time to make a purchase. Anyone know the best source.

[1932 V8]

Just an FYI , if you are not running a 6.00-16 tire the 19 tooth turtle will still not be the right application. If you are running a stock tire size and you still need a 19 tooth turtle, I have one I will give you . Let me know

[JM 35 Sedan]

Originally Posted by Vanspeed

I got a pm from a guy saying he would trade his 19 tooth cap for a 20 but when I count mine it is 21? I feel 21 is the correct number for a 4:11? I see no mention of 20 tooth gears.

There is or was a 20 tooth gear available. I also have one. It could have been used when non standard size tires were used to correct speedometer/odometer readings.

[BoxCar Tom]

3.54:1 gear = 18 teeth = 11-39 on the turtle

3.78:1 gear = 19 teeth = 9-34 on the turtle

4.11:1 gear = 21 teeth = 3-37 on the turtle

[JSeery]

Originally Posted by RobR'35

My mistake. I mean the gear count on the driver gear on the drive shaft for the speedometer.
As to the green book. I've so many other great books but not the green one.
Looks like it's time to make a purchase. Anyone know the best source.

I have several different paper copies but use an digital copy most of the time. Downloaded it for free several years ago. Believe the V8 club has a downloadable source, if not I can try and find one.