gear ratios

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concrete52

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got a 75 dart swinger - 225 slant 6 - going to have a mild rebuild for the motor - be a driver - i have the a904 tranny - might put in the a833 - have the 7 1/4 rear with 2;76 - what can i put in for gears without comprimising too much with fuel economy
 
3.23's would be good but for the price of a new ring and pinion you could probably pick up an 8 1/4 with the gears you want. If you swap in an A-833 down the road you'll have to get a new driveshaft anyways so if you did an 8 1/4 swap and the 833 swap you would only have to do the driveshaft once and you'd get the gears you wanted. Then in the future if you wanted to go with a V8 you could keep your transmission, driveshaft, and rear end. My $.02
 
i am keeping the 225 slant 6 - going with the two barrel set up - and possibly with the a833 i know that what i have in the 7 1/4 are 2.76 gears - i am not into this for race - just a good build - its a full restoration on the 75 swinger - so with the gear selections i am not sure
 
concrete52 said:
i am keeping the 225 slant 6 - going with the two barrel set up - and possibly with the a833 i know that what i have in the 7 1/4 are 2.76 gears - i am not into this for race - just a good build - its a full restoration on the 75 swinger - so with the gear selections i am not sure
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If it were me I would definitely go for a 2.94 gear. I had a volare super six 225 three speed auto and with the 2.76 gears it sucked down gas.especially in the city. On the interstate it was great, but I didn't drive 70 that often. Go with the 2.94 and a smaller tire For in town and highway. You will use the gas pedal less=more fuel in the tank. Besides you could always use a taller rear tire to kind of fine tune your final gear and rpm. I guess it just depends on where you drive most. Strictly city I would go for 3.23 for the stoplight to stoplight. I mean In the city you won't really get over 45 anyway right?:burnout:
 
Also I'm not sure the 3.23 will fit In the 7 1/4. It might be the biggest you can go. You may have to do a little research. Something about carriers being different after the 2.94 gear. The 8 1/4 is also a good swap. Very reliable and you could put whatever gear you wanted in it because it's got a bigger pumpkin. You could source an 8 1/4 but depending on how old it is. I would get it rebuilt for reassurance. Besides it's a full restoration right? All new parts is the way to go. Just my opinion though.
 
check Rock Auto they might still have ring and pinion gear sets for the 7.25 peg leg !
 
alpha13 said:
Also I'm not sure the 3.23 will fit In the 7 1/4. It might be the biggest you can go. You may have to do a little research. Something about carriers being different after the 2.94 gear. The 8 1/4 is also a good swap. Very reliable and you could put whatever gear you wanted in it because it's got a bigger pumpkin. You could source an 8 1/4 but depending on how old it is. I would get it rebuilt for reassurance. Besides it's a full restoration right? All new parts is the way to go. Just my opinion though.
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Uh. Well. Erm. Doesn't gearing have to do with the tooth count on the ring and pinion? It doesn't change the actual size of it, just how fast it turns. You could put 4.11's in a 7 1/4 just like you can put highway gears in an 8 3/4. And yes, some of the carriers won't take certain gears. I believe with an 8 1/4 anything that came with a 2.71:1 ratio or higher (lower numerically, such as a 2.45:1) was a different carrier than anything like a 2.76 or lower (higher numerically). So if someone has 2.76's they can go 3.23's or 4.11's or whatever but if they had like 2.45's then they're kinda stuck with bad gearing. Maybe it's the same for the 7 1/4, maybe not, but I've never had to deal with a 7 1/4. When my car left the assembly line it had a 3.21 geared 8 1/4 rear end and a slant six. Maybe OP lucked out and got an 8 1/4 with a slant too but probably not. And going from a 2.76 to a 2.94 just seems like a waste of money for what you get out of it. 2.76 to 3.21 or something close to that would be better.
 
BlueDream said:
Uh. Well. Erm. Doesn't gearing have to do with the tooth count on the ring and pinion? It doesn't change the actual size of it, just how fast it turns. You could put 4.11's in a 7 1/4 just like you can put highway gears in an 8 3/4. And yes, some of the carriers won't take certain gears. I believe with an 8 1/4 anything that came with a 2.71:1 ratio or higher (lower numerically, such as a 2.45:1) was a different carrier than anything like a 2.76 or lower (higher numerically). So if someone has 2.76's they can go 3.23's or 4.11's or whatever but if they had like 2.45's then they're kinda stuck with bad gearing. Maybe it's the same for the 7 1/4, maybe not, but I've never had to deal with a 7 1/4. When my car left the assembly line it had a 3.21 geared 8 1/4 rear end and a slant six. Maybe OP lucked out and got an 8 1/4 with a slant too but probably not. And going from a 2.76 to a 2.94 just seems like a waste of money for what you get out of it. 2.76 to 3.21 or something close to that would be better.
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All I know is something is different about going to the 3.23 gear. But just saying, you can only get so many teeth on a gear before you have to go bigger. Like I said I don't know what's all involved in changing to a 3.23 in a 7 1/4 besides something not being correct. I have never had the desire to put 4.10 gears in a 7 1/4. Also it does make a difference in rpm with gearing. The gears wouldn't be offered in different sizes if there wasn't a difference. I sure noticed when I went from 3.23 to 3.55 I think it's about a 300 rpm difference. 300 rpm really does make a difference.
 
You can get the bigger gears... I had a 3.90 for a 7 1/4, either way if your just cruising go with a 2.94 or a 3.23. I have a 2.94 and can still break the tires loose! I'll be switching to a 3.23 or 3.55 eventually though as I live in a metro area and don't often get a above 50-55
 
There is some great info about 7.25" Mopar rear end here:http://www.dippy.org/forum2/index.php?topic=73.0

A chart from above web site:

Factory ratios (for 7.25" Mopar) offered include but are not limited to:


•2.26:1 - Used in many civilian M-bodies over the years
•2.76:1 - Used in 80s Dakotas
•2.93:1
•3.21:1 - Used in 90s Dakotas
•3.23:1 - Used in many Slant 6 cars from 1963-1969, and 80s Dakotas
•3.55:1 - Used in 80s Dakotas
•3.90:1 - Used in 90s Dakotas
•3.91:1 - Used in 67 Formula S Barracudas with power-lock
•4.11:1

Aftermarket gear ratios available include but are not limited to:


•2.26:1
•2.76:1
•2.94:1
•3.21:1
•3.23:1
•3.55:1
•3.90:1
•4.10:1
•4.11:1
 
alpha13 said:
All I know is something is different about going to the 3.23 gear. But just saying, you can only get so many teeth on a gear before you have to go bigger....
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While that may be true, the fact is that a 4.10 ring gear could easily have less teeth than does a 3.23 ring gear:

3.23= Ring 42 teeth Pinion 13 teeth
3.55= Ring 39 teeth Pinion 11 teeth
3.73= Ring 41 teeth Pinion 11 teeth
4.10= Ring 41 teeth Pinion 10 teeth
4.30= Ring 43 teeth Pinion 10 teeth
4.56= Ring 41 teeth Pinion 9 teeth
5.13= Ring 41 teeth Pinion 8 teeth

These are typical, and may not be exact ratios for your 7.25", but you get the idea.
 
I like the chart. I'll have to keep that posted in my computer somewhere. Like I said I don't know all there is to know. My brain just got another wrinkle. Lol
 
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