71 up 2.47 to1 and 2.66 to 1

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oldpunko77

oldpunko77

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I havent decide to use either trans for 70 340 duster it now currently 3.23 sure grip factory I have 2.47 to 1 need to be rebuilt or go with factory 2.66 to 1 ?
 
The I like the 1971 up 247 . The ratios are closer together and also steel forks with the scissors style shift side cover. I broke my share of the brass forks over the years. You can use the steel forks in the earlier trans if you cut them.
 
the 2.66 will give you better ability to boil the hides or hole shot, but arguments can be made for the better sidecover and ratios.

it really comes down to what type of driving you're doing.
 
Well basically 340 has chet herbert cam little hotter then stock cam and rest basically 10.1 and old style TRW piston . 30 and J heads 2.02/1.60 and rest stock set up and running 3.55 gears. Plan to change to steel forks and ball and denction set up if I use late 71 trans.
 
the ball and detent side cover is best one. mopar says to use it versus scissors style,
 
I go with 2.66 70 and early box and bought it back from previous buyer who I sold to so now quick fresh up and drop in and go.
 
For a streeter,
those two boxes are so close, it's hardly worth thinking about.
2.66-1.92-1.40-1.00/ splits of .722-.729-.714 versus
2.47-1.77-1.34-1.00/ splits of .717-.757-.746.

This is because, Second gear will get you into speeding territory after about 5.5 seconds, and before you hit Third gear.. The only concern for a streeter, is the first gear difference, which is about the same as one rear gear size, ie
2.47 x 3.55=8.77 and
2.66 x 3.23=8.59 an overall difference of just 2%.

The 2.47 box has shorter splits on all but the 1-2 shift, which is worth a bit of rpm on the shifts at 6000. This might be an advantage in some forms of racing; but, On the street, any stock 318 or bigger can use either with either gear.
But as cylinder pressures drop by installing cams with later closing intake valves; this causes a loss of low-rpm torque, which is when the 2.66 will come out the winner..... with 3.55s
I sure as heck wouldn't replace whatever of those I had, with the other.
If I'd swap either, it would be for a Commando,
3.09-1.92-1.40-1.00/ splits of .621-.729-.714
This, to get a starter of about the same as the other two, requires
~8.60/3.09= 2.76; which really slashes the cruising rpm.
But you know; good luck pulling Second gear with gusto, if you have low cylinder pressure, lol....... which is why I have a 360 pumping over 180psi........... so I can run whatever street rear gear ratio that I please. This allows me to put Second Road-gear right where it needs to be, somewhere in the mid to high 6s.
With a 1.92 Second, this calls for a minimum of 3.55s. But,
with a 1.77 Second, it calls for a minimum of 3.84s........ which is why I sold my 2.47 box; cuz at that time, I had no overdrive.

I've tried many Second Roadgears both higher and lower than 6.80, but always come back to it, sooner or later. It's just a really fun gear in town, and I can just leave it in second most of the time, cuz it goes at the rate of 11.8mph per 1000rpm, which is from; 30mph@2500, to 60@5000, and even to 85mph@7200

Happy Hot-Rodding
 
My self I always liked the 247 close ratio as a good trans to play with on the street. Also the 72 lower HP 340 cars really took advantage of the close ratio. The 70 TA and AAR's proved the better ratio spread and it was use from then on. Even the Hemi boxes were changed to 244 in 71. Mopar new they were on to something.

We used this same knowledge when racing the dirt track nationals with ATV's. We would install Dirt bike trans gears which were higher ratios then in the ATV. Instead of a hole shot in secomd as everyone did so not to shift almost instantly we would leave in the higher 1st of the dirt bike trans. The ratio change was so close it would just constantly pulled through gear changes. This is just my input from what we tried racing and street driving for many many years.

This is seat of the pants info not from paper.

Info from Brewers site.

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steve 016.jpg
 
My A833 decodes as 68 Dart, so that would mean 2.66 first. The part I am confused on is reference to large or small spline? What is that referring to?
 
That would be the spline-count on the output end of the Mainshaft.

A-body
A833 overdrive boxes can be found at Swap meets in either flavor.
the slanty-boxes have the 904-sized shaft.
the 318 boxes can be found in either 904 or 727 sized shafts
As to Non-od boxes, IDK but;
All performance V8 boxes have the 727 sized shaft.
As to non A-bodies, I think they were all 727-sized.
 
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shaft is based on input whether it was 23 spline or 18 spline and dia of shaft. 18 is way bigger
 
18 spline also known for hemi box where belong to 440 and hemis. And rest of 23s pretty much everything except the od main shaft drive usually smaller 26 spline same as 904s where the yokes slide in and early 64, 66 also has small spline 26s 67 and up has 30 spline same as 727s.
Pretty much as AJ has stated.
 
AJ/FormS said:
That would be the spline-count on the output end of the Mainshaft.

A-body
A833 overdrive boxes can be found at Swap meets in either flavor.
the slanty-boxes have the 904-sized shaft.
the 318 boxes can be found in either 904 or 727 sized shafts
As to Non-od boxes, IDK but;
All performance V8 boxes have the 727 sized shaft.
As to non A-bodies, I think they were all 727-sized.
Click to expand...
Small spline is 23 spline input. Large spline is 18 spline input / Hemi 4 spd.

All transmissions that are not 18 spline are 23 spline and are considered small spline. They did make a 30 and a 26 spline main shaft / output shaft for short tail A-F body transmissions. That is not what they are talking about in the diagram above.

Main shafts are all interchangeable with cases and gear sets except OD's they are a different diameter internally. Which gets into more depth then being discussed. The only thing that needs to be changed when going 30 to 26 main shaft is the tail shaft which is only available for A-F body transmissions.

What I do know is you can take an F-body aluminum case and tail shaft and install a 18 large spline /Hemi internals into it using the 30 spline main shaft from an A-body. Yes the front bearing cover bolts right on from the Hemi box. Then if you take the side cover from an overdrive truck trans and install it you will have an all aluminum hemi 4 spd. for an A-body car.

Below are two pictures of Hemi transmissions. One is a standard synchronized trans. The other is a liberty non synchronized trans , Shift without the clutch. Know as the crash box back in the day. They were used in mopar and other brands for racing. The 3rd and 4th pictures show a mopar input and a GM input

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106_0617.JPG


106_0627.JPG


106_0626 - Copy.JPG
 
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Weirdly mine has the 30 spline output even tho its a 68 Dart A833... Is that odd?
 
Seems 67 A body would be 26 output, and 68 up A body is 30, based on what i read on Brewers.

My car is a 71 Duster with 71 small block K, 440 using Schumacher mounts and 727 trans. What are the chances that my driveshaft will be the right length with the A833 that is going in?
 
Muswagon said:
Seems 67 A body would be 26 output, and 68 up A body is 30, based on what i read on Brewers.

My car is a 71 Duster with 71 small block K, 440 using Schumacher mounts and 727 trans. What are the chances that my driveshaft will be the right length with the A833 that is going in?
Click to expand...
Zero. If it’s an A body 833 it’s a few inches shorter than a 727.
 
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