Slant 6 and 318 trans options

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Johnny71dusty

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I’m searched this site too to bottom and no one spells it’s our clearly what the transmissions are called . I need actual numbers to buy a new one or look at swaps . How many options are there and what are they actually called

What I want is to remove my slant 6 motor and 3 on tree transmission ( don’t know what it’s called and can’t find ) and put in a 318 but a 3 on the tree trans option still ( can’t find what that trans would be either )


1970 duster

slant 6 auto =904
Slant 6 3speed manual on floor ?
Slant 6 3speed manual on tree ?

318 - auto =904 but with different casting ?
318 - auto = 727 ?
318 - 3 speed manual on floor ?
318 - 3 speed manual on tree ?
 
I would start by wandering over to the MyMopar site and download a service manual for your year (you may have to satisfy with Dodge/ vs Plymouth, as well as get a year or two older/ newer and download those as well

The problem is that "actual numbers" are not always used. You can put EITHER a 904 or 727 auto behind a 318. A 727 for a slant is rare and hard to find. The are in fact different main housings between slant/ small block, and big block AND be aware there are some oddball Chrysler autos that THE CASES WERE CAST to fit AMC or other engines, and therefore will not fit any Chrysler

The 904 is same length as an installed 3/4 speed stick, while the 727 is longer, so takes a different driveshaft

The same transmission can "sorta" be used for either floor or "tree" (column) shift but I don't think the older box was used in floor shift. The older box is easily identified by a top cover, the newer "all syncro" (and stronger) 3 speed has a side cover more like a 4-speed

The lighter duty, older design, and not synchronized into 1st gear box is an A903
The heavier duty, newer design, "all synchro" box is an A230
 
The A903 is most likely what you have because of the slant and three on the tree Duster.
They also made the A745 (looks the same as a A903) that was used for Taxi and Police 6 cylinder cars.
You can use the A903 behind a 318 with the right Flywheel,Clutch/Pressure Plate and Bell Housing.
You also can retain the column shift. You may want to look at the data tag/fender tag on the left front inner fender.
The lowest row of numbers on the tag,second from the left will be a 3 digit number.Most likely starting with a letter.
THIS IS UNLESS YOUR CAR CAME FROM THE LYNCH ROAD PLANT.
If so the trans code will be the third set of digits. I do not know what the code is for a A903.Going to My Mopar as
67Dart273 stated and doing some research is what you need to do.
Fun huh ? Welcome to the Mopar world.
 
3 on tree transmission (
three on the tree, has traditionally always meant a 3-speed manual trans, column-shifted.
IIRC the 70 Duster was the First year that the A230 full-synchro was available, and only on a 340. But it will fit on any SBM. And it can be installed into your Duster with relative ease, no matter what previous trans was in it. The tough part is installing the correct clutch pedals.
I wouldn't try to shift that A230 on the column tho; it kindof defeats the whole purpose of installing it, cuz column-shifters are notoriously slow and problematic when pushed hard.

As for the A230, it comes in two flavors; Which are;
2.55-1.49-100 close-ratio and
3.08-1.70-1.00 wide-ratio
You cannot tell them apart by looking. You shift them into first and count the number of turns that the input gear makes with one turn of the output shaft.
Either trans will bolt onto the 318 bellhouse; and the bonus is, that the A230 is the same length as any trans that ever came in an A-Body except the A727. And it will work with the 1970 speed-O cable.
So if the car currently has a clutch pedal, the A230 is what you want.
If your car will be a cruiser, then the 3.08 wide ratio will allow a 20% reduction in rear gear for same take off and so the hiway rpm will be 80% of whatever you changed from. But the downside is that if you install a 2.76, she will be pretty gutless in third gear.
If your car will be more geared for city and performance, then you would want the 2.55 close-ratio, with a big-number rear gear.

So as a cruiser, with 2.76s already installed, the starter gear is reasonable at
2.76 x 3.08=8.50 And the rpm on the hiway with 26.7 inch tires will be around 65=2250
But if you installed the close-ratio box your starter would be a pitiful 2.76 x 2.55=7.04

As a streeter, using the 2.55 box and 3.91s, your starter gear is
3.91 x2.55=9.97 a very nice number. But your 65=3200
Second gear will come around 40 mph@5000rpm, and go to 4500=61mph or 68@5000 Very nice numbers for a stock long-block 318.

Good luck.
 
Remember the Slant to V8 swap takes some doing. It just don't bolt right in.
Conversion mounts are necessary or a K-Frame swap
 
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