How do I ID a 4 speed, overdrive or not?

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392Mopar

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Hey guys,
I recently got a 72 Duster with a 318, 4 speed. It was originally an auto, /6 car. How do I determine what kind of tranny is in the car, did they come in regular and overdrive? I'm running 25.5" rear tires, a rear out of an F-Body with 2.90's I believe, and I can go down the parkway doing 65-70MPH and only be turning around 2000RPM. Just driving down local hyways, doing 50-55ish I never take it out of third. I'm quessing a little cause I dont have the speedo hooked up yet, but does it sound like a standard 4-speed or maybe an overdrive unit?

I'm asking cause I want to get new rear gears to wake up the mildly worked 318 and I'm trying to decied a good ratio for performance without the car screaming when I'm doing 55-60. I was thinking 3.91's but I found a 4.10 unit, think that would be a bit much? Also I plan on running 27-28" rear tire in the near future.

Thanks

Butch
 
The simple way to check is to crawl under the car and look at the levers the linkage attach to on the side of the tranny cover. If the one closest to the engine points down and the one to the rear points up its an OD unit. If they both point up then its a standard 4spd.
 
Weren't OD 4 speeds aluminum cased? Also, they were 76-later. If outside the car they had the larger front bearing retainer.
 
C130 Chief said:
Weren't OD 4 speeds aluminum cased? Also, they were 76-later. If outside the car they had the larger front bearing retainer.
Click to expand...

Not all were aluminum. The early '76s were iron case. I have one that was assembled in April '76 and has an iron case. Think the aluminum case came on line in June '76. Will agree that if you find an aluminum case 4 speed it will more than likely be an OD. The only way to be sure is measure the bearing retainer. If it 5.125" it's an OD.
 
Ok I'll take a look at the levers and see how there configured. But as far as measuring the bearing retainer, this is my fist manual transmision car, where is the bearing retainer. I know nothing off manual trannys, I plan on correcting that but for now I'm in the dark, always been an auto man. Thanks

Butch
 
The bearing retainer is the round piece bolted to the front of the tranny with a tube on it that the through out bearing rides. The protruding diameter (5.125) actually acts as a register for the tranny into the bell housing. You can not see it if the tranny is in the car. Plus the retainer can be swapped for a smaller one (4.80").

If the tranny shifts correctly then the lever direction on the side of the tranny is the most positive way to tell. If the levers were installed incorrectly then the tranny would not shift right (i.e., 3rd where 4th is and visa verse).
 
Thanks for the info. I went under today and its got one lever up and one down. But a major tip off is that its all aluminum, seems like its an overdrive. On the drivers side I saw the #'s C13546 B , any ideas what its from? I quess thats why I can cruise at 70 and run 2000RPM with 2.91's.

So Next questions is, with an overdrive tranny what kind of gears can I run with a 27-28" tire and still be streetable?

Thanks

Butch
 
grumpuscreature said:
Not all were aluminum. The early '76s were iron case. I have one that was assembled in April '76 and has an iron case. Think the aluminum case came on line in June '76. Will agree that if you find an aluminum case 4 speed it will more than likely be an OD. The only way to be sure is measure the bearing retainer. If it 5.125" it's an OD.
Click to expand...

75' first year, a had one.
 
I have an A833OD with 3.55 gears and 27" tall tires. It runs a tick over 2000 rpm at 65mph. I was going to go with 3.73's but Randy's was back ordered on that ratio and I hemmed and hawed for a while between the 3.55's and 3.92's and finally went with the 3.55's.

I have not regretted the choice, the car is a street cruiser but even so I have run a best of 13.7 @ 102 mph with the combo and its not gears or HP that is holding it back. As the miserable 2.2 60' time on the 13.7 run will attest I have tracktion issues.

The A833OD tranny has a very low first gear so going step on the rear gears will make first almost useless. 3.92's is about as steep as you would want to go.
 
Nice, looks like 3.91's should fit the bill then. I'm gonna try to find a used set to run for now and I know I wouldnt find anyused 3.73's for an 8 1/4. Sounds like a nice combo you have there, nice cruising car that will boogy if you want it too, nice. Thanks for the info


Butch
 
392Mopar said:
Hey guys,
I recently got a 72 Duster with a 318, 4 speed. It was originally an auto, /6 car. How do I determine what kind of tranny is in the car, did they come in regular and overdrive? I'm running 25.5" rear tires, a rear out of an F-Body with 2.90's I believe, and I can go down the parkway doing 65-70MPH and only be turning around 2000RPM. Just driving down local hyways, doing 50-55ish I never take it out of third. I'm quessing a little cause I dont have the speedo hooked up yet, but does it sound like a standard 4-speed or maybe an overdrive unit?

I'm asking cause I want to get new rear gears to wake up the mildly worked 318 and I'm trying to decied a good ratio for performance without the car screaming when I'm doing 55-60. I was thinking 3.91's but I found a 4.10 unit, think that would be a bit much? Also I plan on running 27-28" rear tire in the near future.

Thanks

Butch
Click to expand...
4.10s and a 27 28 inch tire will be like running a higher gear. just like gettin 3.91s with what you have now. so if you even go back to stock tire that gear is goin to feel lower. find out what you have in the rear now. i have 2.76s. there good for the highway. im thinking you might have 3.23s or so. i want a 4 speed a 4.10s. or a 5 speed and 4.56s
 
Well I ended up getting a great deal on a narrowed 8 3/4 out of a 70 Duster. It is is about 4 inches shorter drum to drum than a stock A-bodies, and it has strange axles with the 5 on 4 1/2" bolt patern. And it looks like the spring perches will line up perfectly with my Duster with the 3" inboard spring kit. But for now it has a 4.88 sure grip chunk!!!!!! I'm probably gonna put it in the car as is for now and have some fun before buying or trading for a 3.91-4.10, gotta save up some $. Should be interesting!

Butch
 
the first gear ratio in that box is 3.09..with a 27/28 tall tire and 4.88 rear gear, you will neeed to hold on the the shifter before you floor it LOL.

the RPM is gonna come up very quick,,if you have room for a taller tire go with it,then you wont have to spend the bucks for another gear,,

i have a FORMULA S box in my barracuda,,,same first gear as yours 3.09

i have 4.56 rear gears and 33 inch tall tires,,but my 4th gear is a standard 1to 1 ,,the 33 inch tall tire and 4.56 work out to a final drive of 3.89..just shy of a 3.91..so at 60 on the high way my RPM is 2850,, not bad,, but an O.D is in the plans sooner or later,,,

the 4th in your box is a .68 reduction,,im guessing your RPM drops around 800/900 RPM,,???

find out how much it drops and then figure out where you want it at when cruising to determine your tire and rear gear ratio needs,,
 
fstfish66 said:
the first gear ratio in that box is 3.09..with a 27/28 tall tire and 4.88 rear gear, you will neeed to hold on the the shifter before you floor it LOL.

the RPM is gonna come up very quick,,if you have room for a taller tire go with it,then you wont have to spend the bucks for another gear,,

i have a FORMULA S box in my barracuda,,,same first gear as yours 3.09

i have 4.56 rear gears and 33 inch tall tires,,but my 4th gear is a standard 1to 1 ,,the 33 inch tall tire and 4.56 work out to a final drive of 3.89..just shy of a 3.91..so at 60 on the high way my RPM is 2850,, not bad,, but an O.D is in the plans sooner or later,,,

the 4th in your box is a .68 reduction,,im guessing your RPM drops around 800/900 RPM,,???

find out how much it drops and then figure out where you want it at when cruising to determine your tire and rear gear ratio needs,,
Click to expand...


Thanks for the input fstfish66. The Dusters gonna be mainly a street car so 28" tire is max without cutting the quarters. I'm sure I'm gonna have to be fast at shifting but it will only be for a little while till I can afford a used chunk. I may even look into a cheap one-legger and either swap in the sure grip or use the open then sell the whole 4.88 suregrip chunk to almost pay for another chunch with better gears.

I had 3.91's in my 68 Satellite with a 440/727 but I think that had 29-30"tires. But I has happy with its street maners.

Butch
 
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