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Expert
Posts: 2207
 
Location: Muskego, WI | Is this a bolt together affair?
1966 318 Poly V8
1998 Dodge Dakota 3.9 V6 (same bolt pattern as 5.2 V8) bellhousing, external slave cylinder
Dodge Dakota flywheel, starter, clutch (disc and pressure plate), fork, pilot and release bearings
AX-15 5 speed, external slave configuration
I have driven many Jeeps with this transmission behind a 4.0, really like how they perform. People are putting these transmissions behind LS1 V8s, so should be able to handle my stock 318 Poly. |
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Exner Expert 10K+
Posts: 10108
Location: So. Cal | As long as the 3.9 V6 is internally balanced, and you don't have issues with getting a newer style pilot bearing into the crank of the 318, then I don't see why it wouldn't work. But you will also need to consider the location of the shifter. A truck style shifter doesn't usually come out in the same location as it would on a car. |
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Expert
Posts: 2207
Location: Muskego, WI | Here are a few more links with info on this topic. Since my 318 Poly is a 1966, it shares the same crank flange, bell housing bolt pattern and dowel pin location as the LA and Magnum series engines (I currently have a late 1970s Dodge Aspen bell housing on my 318 Poly to use with my A833 OD trans). This will probably end up being my ultimate goal as it will bolt up with stock, off the shelf parts AND allow me to use a standard fork and throw out bearing with an inexpensive and easily replaced external slave cylinder.
First gear is really short (3.83) and overdrive isn't as long (.79), so I might even move to 2.94 gears (which I have). Here are the final/combined gear ratio comparisons in each gear, with the A833 with 3.31. gears on left and AX15 with 2.94 gears on the right.
1st: 10.23 vs. 11.26
2nd: 5.59 vs. 6.85
3rd: 3.31 vs. 4.23
4th: 2.42 vs. 2.94
5th: NA vs. 2.32
The A833 also has a pretty drastic ratio drop between 1st and 2nd, 45.4%. The AX15 greatest drop between gears is 39.2% (also from 1st to 2nd).
https://www.jalopyjournal.com/forum/threads/ax15-behind-a-318-poly-s...
https://www.novak-adapt.com/catalog/bellhousings/amc-ax15-bellhousin...
http://www.jeepforum.com/forum/f12/v8-s-mount-directly-ax-15-a-1376...
Edited by jboymechanic 2018-06-29 8:53 AM
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Exner Expert 10K+
Posts: 10108
Location: So. Cal | I run 2.76 gears in my '68 Barracuda with a standard 4speed. I can just barely get away with it because the car is so light and the 340 motor is strong. You have to rev up the motor quite a bit before you let out the clutch or it will kill the motor with the high geared 1st. 2.94 gears would be much better for my Cuda. With a larger, heavier car with less power like you have, 2.94 is going to be pushing it. I think you will be better off with 3.23 or 3.15, a little higher than your old 3.31.
Edited by Powerflite 2018-06-29 9:36 AM
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Expert
Posts: 2207
Location: Muskego, WI | So you think accelerating in first will be the issue? The 318 poly is rated at 340 foot-pounds at 2,400 RPM, while the 4.0 is rated at 225 foot-pounds at 4,000 RPM (both numbers according to allpar.com). Advantage --> Poly. The Jeeps with the 4.0 and 5 speeds had 3.07 gears, so the Jeep would have about a 4.5% gear ratio advantage, but taller tires and much less available torque. Also, with a 3.83 first gear and 2.94 rear gears, I will still be LOWER than the 3.09 first gear and 3.31 rear axle that I currently have.
For top end I'm not worried either. A final drive of 2.32 may be really low, but my 1982 Chrysler Cordoba had factory 2.24 gears behind a emissions choked 318 LA that was rated at about 100 less hp and torque than the Poly. Surprisingly, that car actually drove great at 75 mph and would deliver 28 mpg on highway trips between Madison, WI, and Minneapolis, MN.
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Elite Veteran
Posts: 910
Location: Peoples Republic of Oregon | ...sounds like a good swap to me...... |
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Expert
Posts: 2207
Location: Muskego, WI | Gary,
Have you done one of these swaps? I know you popped into the conversation on the HAMB, is this a true bolt together job? I know I'll have to mod my cross member and mount and cut a hole for the shifter, but everything between the engine and trans should go together easily, right? |
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Elite Veteran
Posts: 910
Location: Peoples Republic of Oregon | I haven't made this exact swap but have sold plenty of adapters to folks who stated the AX15 was the intended trans.
The 3.9 block is the same bolt pattern as the 318P.
The 6-bolt crank flange is the same.
The late pilot bearing, pn 53009180AB, fits all post-62 cranks except for the odd-ball 273.
The 3.9 should be externally balanced like all late engines but, the flywheel is just a big lump of iron....rebalance it.
Check the flywheel that you have, it should have 143 tooth count, same as the mid-8's 360.
Replacement clutch/PP/TO bearing are available just about everywhere.
Some of the Jeeps/Ram1500 used a hyd slave and some used a hyd T/O bearing; the front bearing retainer dictates so keep what you have.
The gear spreads can't be all that bad since they get swapped into alot of different car/engine packages. The trans itself is plenty stout.
Nope, looks like a good swap to me. |
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Expert
Posts: 2207
Location: Muskego, WI | Thanks for the tips Gary! Part numbers are greatly appreciated for reference also. I'm after the external slave setup, which is a common retrofit in the Jeep world as the hydraulic TO bearings have a tendency to fail. |
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Expert
Posts: 1444
 
Location: Oconomowoc Wi | Jon and Gary, I'm looking for a AX15 now, having issues finding a reasonable 2wd version locally, but still looking. The 1959 Dodge sits with a 60 361 and automatic currently. so I'm in the market for a workable motor too I guess.
The thread may be from 2018, but still feels relevant. |
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Elite Veteran
Posts: 910
Location: Peoples Republic of Oregon | Bart, this type of swap is always relevant....at least as long as we are 'allowed' to own such horrible pieces of air polluting auto history. ;(
Keep in mind that the AX15 has a very unique bolt pattern to the bell so the same bell must be used and it is only for the A-LA block pattern and requires a 143 tooth flywheel.
If you are creative and have a milling machine an alum BB bell could be carved up... |
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Aisin Warner AX-15 behind a post 1962 318 Poly
