Change gearbox gear ratio

[De Konjel]

Is it possible to change the gear ratio on a Model A gearbox?
Are there aftermarket gears available?

[nkaminar]

Your best bet is to buy a Mitchell transmission with the close ratio. As a bonus you will get synchronized second and high.

[JayJay]

Originally Posted by nkaminar

Your best bet is to buy a Mitchell transmission with the close ratio. As a bonus you will get synchronized second and high.

This is the only way I know of. In hindsight I sort of wish I’d done this instead of rebuilding my stock tranny.

[Y-Blockhead]

You will love the Mitchell Synchro Transmission. Get the one with 15% over 1st and 2nd. Takes that big gap out of the 2-3 shift. I often wish I had bought the Mitchell transmission first instead of the Mitchell O/D, although they both have their place.

[JayJay]

Originally Posted by Y-Blockhead

You will love the Mitchell Synchro Transmission. Get the one with 15% over 1st and 2nd. Takes that big gap out of the 2-3 shift. I often wish I had bought the Mitchell transmission first instead of the Mitchell O/D, although they both have their place.

Y-B and others who have both Mitchell transmissions and Mitchell O/D: I currently have a Mitchell O/D and use 2O as an intermediate between 2 and 3, especially for climbing hills. However, I still find a significant jump from 2O to 3. Do you find that you use 2O in this manner even though the Mitchell transmission puts 2 closer to 3?

[Y-Blockhead]

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Originally Posted by JayJay

Y-B and others who have both Mitchell transmissions and Mitchell O/D: I currently have a Mitchell O/D and use 2O as an intermediate between 2 and 3, especially for climbing hills. However, I still find a significant jump from 2O to 3. Do you find that you use 2O in this manner even though the Mitchell transmission puts 2 closer to 3?

Yes, I usually shift from 1st > 2nd > 2nd O/D and shift to 3rd if needed. I try not to drive on freeways, so 3rd O/D doesn't get used much.

Much of the time I use just 2nd and 2nd O/D.

[Y-Blockhead]

BTW, I also extended my O/D shifter ~4" so I don't have to reach so far.

[nkaminar]

Y-B, Good idea. Did you make that yourself? I see where it has male threads at one end and female treads at the other. Is it chrome plated or stainless steel?

[Y-Blockhead]

It is stainless steel. I had a piece of thick wall stainless tubing with the correct size O/D and tapped the inside so I could thread it onto the Mitchell shifter. On the ball end I just cut off a bolt.

[Jim Brierley]

It is also easy to install a V8 trans, by using a kit available from Bert's in Denver.

[Charlie Stephens]

Now an answer to your question. I have been into Model A's since my first one in 1961 and have never heard of aftermarket gears with a different ratio.

Charelie Stephens

[Gene F]

That extension. Reminds me of an extension Jegs sells for peep sight mirrors. Ya never know...

[Gene F]

Originally Posted by Jim Brierley

It is also easy to install a V8 trans, by using a kit available from Bert's in Denver.

The benefit of this would be what?

[nkaminar]

I remember a You Tube video of someone custom making gears for the Model A transmission. I am not going to try and find it. i remember that it was a lot of work and that the man who did the work had to redo it to make it right. It probably cost him in time and money at least twice what a new Mitchell transmission would cost, or more. The gears were machined and then hardened.

[Y-Blockhead]

Here is an interesting video by Astra- Werke on modifying his transmission. Ya gotta give him an A for effort. https://www.youtube.com/watch?v=IfetbWkWVaE&t=1096s

[Y-Blockhead]

Originally Posted by Gene F

The benefit of this would be what?

Better ratios and synchros??

[nkaminar]

Y-B, Thanks for digging out that video. That was the one I remember. A lot of work.

[updraught]

A 3.27 ratio diff will give %15 over on all gears.

[Y-Blockhead]

Originally Posted by updraught

A 3.27 ratio diff will give %15 over on all gears.

Yeah but you still have that big gap between 2nd and 3rd. The Mitchell trans makes 2nd and 3rd ratios closer together.

[JayJay]

In an attempt to answer my own question, I did some calculating of the final transmission ratios with standard and Mitchell transmissions, and with/without Mitchell overdrive. Interesting - see attached.

It appears that with standard transmission and Mitchell O/D, the jumps from 2 to 2 O/D to 3 to 3 O/D are about the same - a gear reduction of 26-27% (I'd guess that might be part of why the 26% O/D ratio was selected). The jump from 2-3 without the 2 O/D in between is substantial - a gear reduction of 46% (this is the 2-3 gap we're all familiar with and that Y-B alludes to above).

With the Mitchell transmission first and second gears at 15% higher, the jump between 2 O/D and 3 narrows considerably, about half. But you get that back in a reduction between 2 and 3, the jump is about 28% less.

So with a Mitchell transmission you get a narrowing of the 2-3 jump coupled with synchromesh 2 and 3. You "pay" for that with a narrowing of the 2 O/D to 3 gap. Overall top end remains unchanged.

Have fun. Now back to our normally scheduled programming.