Mitchell Tranx 15% Higher Ratio?

R

Ron/IA

Well-known member
I have been trying to get my mind wrapped around the ratios of the standard A transmission, versus the Mitchell 15% higher ratio (1st & 2nd gear) transmission.

The A transmission ratios are: 1st-8.75:1; 2nd-6.89:1; 3rd-1:1

My mind tells me with a 15% higher ratio in the Mitchell; that gear would have a lower speed than the standard with the engine running at the same RPM in each case. What would the Mitchell transmission ratio numbers be at 15% higher. (1st-10.1:1; 2nd-7.92:1; that's if I am doing the math correctly. Which I am not sure I am.)

I am wondering why would a person want the higher ratio? Or, am I not thinking correctly? Or, is the 15% increase higher speed?

Can someone explain this to me in plain English?

Thanks,
 
the A trans has a small RPM drop from 1st to 2nd and a big one from 2nd to 3rd. the mitchel 15% makes all shifts more equal which is nicer to drive and better in hilly areas.
 
Jim good to hear from you. I'm enjoying your book & yes I checked the labels on all my t-shirts.
 
Like Jim said, the original has the 2 lower gears geared very low apparently for the road conditions of the day. I think the higher gearing [ higher speeds] available in the Mitchell unit would be a welcome improvement for most conditions today.
 
Jim & Patrick - I appreciate your responses; I was thinking those terms might be the way things were. That makes sense to me now.

My memory is now telling me there was a vendor at one time had a set of gears that fit in a standard A transmission, and equal out the ratios. Does anyone remember that?

Also, the A transmission ratios are listed a 3rd-100%; 2nd-53.8%; 1st-32.04%

How are those percentages calculated?

Thanks,
 
If someone does make a gear set with somewhat higher gearing, I'd sure be interested. That I'm interested in, the syncro not so much.
 
Ron/IA said:
Jim & Patrick - I appreciate your responses; I was thinking those terms might be the way things were. That makes sense to me now.

My memory is now telling me there was a vendor at one time had a set of gears that fit in a standard A transmission, and equal out the ratios. Does anyone remember that?

Also, the A transmission ratios are listed a 3rd-100%; 2nd-53.8%; 1st-32.04%

How are those percentages calculated?

Thanks,
Click to expand...

It can be confusing and people think of ratios differently and list them as such. A rear end with 4.11 to 1 is a higher numerical ratio than a 3.78 to 1 ratio, but the 4.11 to 1 is a slower speed ratio. That's why I now call the ratios higher speed or slower speed rather than higher or lower ratio.

In the first post you mention first and second gears, which include the rear end ratio, then third gear doesn't include the rear end ratio. I know you took these from some book, and that book has a dumb way to list it. I've seen it listed that way in some book, but don't recall which book. It makes it confusing if you don't realize how what's going on. It also assumes that everyone has the same rear end ratio, which of course they don't, even though 3.78 is by far the most common.

BTW, I'd like a low ratio 3.27 for my Model A.:D
 
Ron, I believe the Mitchel being 15% Higher the ratio is actually 15% Lower numerically. ie; A 3.55 rear end ratio is considered Higher than a 4.11 gear set.

So the A ratios you stated would become 1st-7.44:1, 2nd-5.86:1, 3rd-1:1. Hope that helps.
 
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I run both the Mitchell overdrive and the 15% higher ****** in my Cabbie. Much more user friendly in traffic than the original ratios.
I kinda miss the finesse of driving the non-syncro, but my couldn't handle it.

Dick
 
Tom - The ratio info I got from the specification page in on Mac's web site. Interesting the ratios I mentioned would include the rear end ratio.

Y - I too now believe the higher ratio referred to by Mitchell is meaning "higher speed"; not a higher numerical ratio.

Again, I ask; does anyone know or remember gears made for the standard Model A transmission that would make the ratios more even?

Thanks,
 
The Model A standard transmission ratios are 1st: 3.12/1, 2nd: 1.85/1 and 3rd: 1/1. I don't know where Mac's gets those ratios, but they go around and are wrong. Maybe they are calculating a final ratio, including the rear end ratio. However, the final ratio is found by multiplying the trans ratio by the rear end ratio and I can't figure any ratio that matches any rear end ratio I am aware of. I do not know the truck rear end ratios. Best thing would be to call Mitchel and ask them the ratios. I have not heard of any other gearing that would fit in the A trans that would even out the shift.
 
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All I can tell you is I have driven several Model A Fords with the Mitchel with the 15% HIGHER first and second gears, and all I can say is, it is the perfect ratios to make the car drive so much nicer.
 
Think about it this way; which ratio is higher? 1:1 or 2:1?

1:1 is higher than 2:1...it's the same way with gear ratios; a 3.54 (3.54:1) rear end is higher than a 4.11 (4.11:1) ratio.
 
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