I have recently aquired a 72 Duster with a /6 automatic. The engine is junk, so I'm pulling it and the trans to install a 340/727 combo. I understand that I need conversion mounts for the engine to bolt into place in the factory /6 K member. Can the transmission cross member be reused with the 727? I assume the trans mount will be different as well. Will the slant 6 torsion bars sustain the weight of the small block setup long enough for me to sort out any issues from the swap? I will be keeping the stock 7.25 rear in the car for a little while, until I can source a suitable replacment. Can I retain the stock driveshaft length if I simply swap the yoke? All of my other Mopars have 4 speeds so this is my first delve into the automatics and I know nothing about them.
/6 to 340 swap
- Thread starter A Mopar
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Same cross member, same mount, shorter driveshaft.
Professor Fate
Push the button, Max...
The crossmember (and mount) can be used regardless of transmission-904, 727, four speed, all the same.
The 904 driveshaft can't be reused with a 727, the transmissions are different lengths. It might be a tough pill to swallow, but if you plan on replacing the rear end, now is the time- otherwise you'll just have to have yet another driveshaft made up again later.
You should be able to make the stock linkage work with the 727, and the speedo cable will just switch right over too.
Swap mounts are available from Schumacher or TransDapt
'67-72 A-Body Slant 6 to 273/318 or 340/360
https://www.hedman.com/product-detail/4695
or you can make your own using a standard A body 340 driver's side bracket and a truck LA passenger side bracket.
abodyjoe
Well-Known Member
while not ideal they will hold the car up enough to drive around until you can do larger bars.
abodyjoe
Well-Known Member
if you can find a v8 904. you'll be able to keep the existing driveshaft and its quite a bit lighter.
abodyjoe
Well-Known Member
abodyjoe
Well-Known Member
lol.. that a load of crap. 904 is the better trans. no way i'd be running a boat anchor 727.
In normal daily driving with stock small blocks, or /6s 904s don't hold up worth a shyt for me...I've scrapped more 904s and replaced them with 727s than I can shake a stick at
plumkrazee70
Well-Known Member
Lol. Crazy how soo many people have different experiences. I drove a mild 318/904 for years with no issues. Lots of drag strip passes and burnouts.
abodyjoe
Well-Known Member
then you or whoever is building transmissions for you have no idea what you are doing.
Never had to rebuild a 727. Adjust the bands, change filter and fluids, up the pressure, install a 4.2 kickdown lever, replace the seals, good to go. My only exception is early A-Body, then I'll run a 904 if it doesn't have a 4 speed.
abodyjoe
Well-Known Member
i've beat the ever living **** out of 904's for many years and never had to pull one apart because i hurt it. have friends running in th e10's and 11's that have been running the same 904 for many many years without pulling them.. 904 every day for me.. you 727 guys can have them.
Unconventional
Well-Known Member
The guy that built the Powerglide for my partner's injected alcohol dragster told me he could build a 904 for as much horsepower as I could think about putting in front of it.
I've never had many cars that could even do a burnout if I tried/ which I honestly never tried much.... And even at that 904s don't hold up.
I've never owned anything but Chrysler products in 40 years of being a licensed driver.
I've rebuilt transmissions before, sent some out for bench rebuilds, but never really knew how to "beef one up". So most I have done have been stock overhauls. The more recent ones a mild shift kit maybe...
Though my first experience with a shift kit was on one of the first transmissions I was ever into was back in the 80s on a Cordoba, I put a b&m one in and was never happy with it, didn't need the 2nd gear bark every time it went thru the gears so that steered me away from any mods for many years after that..
Anymore I use a transgo, the mildest one they sell.
I've never owned anything but Chrysler products in 40 years of being a licensed driver.
I've rebuilt transmissions before, sent some out for bench rebuilds, but never really knew how to "beef one up". So most I have done have been stock overhauls. The more recent ones a mild shift kit maybe...
Though my first experience with a shift kit was on one of the first transmissions I was ever into was back in the 80s on a Cordoba, I put a b&m one in and was never happy with it, didn't need the 2nd gear bark every time it went thru the gears so that steered me away from any mods for many years after that..
Anymore I use a transgo, the mildest one they sell.
Never smoked a 727, I've smoked a few 904s, non built.
abodyjoe
Well-Known Member
I've never smoked a 904.
IfItsGotWheels
XS Tech-Anything worth doing, is worth doing in XS
I've smoked 2 727s, both professionally built, with the same built 340. I have yet to kill a properly built 904.
The 340/727 combo came with the car so I'll stick with that for now. The 340 appears to be a stock forged steel crank 1971 engine. If the 727 grenades I'll probably put a 4 speed in it since I've yet to hurt one of those and the 3rd pedal is more fun for me to drive anyway. I didn't expect such a debate on the transmission haha. Thanks everyone for the input.
Ant
Well-Known Member
Sounds like a good combo. I was thinking of going with a 727 for my car, but I bought the engine and 904 together, so I'll break that first lol.
Anyway, good luck with the swap, it should be a fun car when done.
Furious65
C-body Guy
I've smoked three stock 904's all behind either stock or very mild 318's. First two were back in the 80's, I'm pretty sure they were all original, and the last one was rebuilt professionally and crapped the bed right after the warranty ran out. Since then it has only been 727's for me. Never have smoked a bone stock 727 behind a stock or mild engine including BB's.
Boat anchor? How much more does a 727 weight vs a 904? Seriously, I don't know. I know the old saying is that a 727 will cost a you a tenth in the 1/4 but I would rather have the extra strength of the 727 than that tiny bit lower ET.
Ah, operative word... properly. That means that those two 727's were built professionally but not properly.
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