904: should I switch to 727?

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75Chimera

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Hi, new to the group!

I picked up a 1975 Dart Sport recently, supposed to have a 360/727, Sure Grip rear. The engine and rear end check out, but the transmission is actually a 904. It is a former hole shot car. I couldn't get under the car when I bought it because it sits REALLY low, and has those horrible ground-dragging headers. Anyway...

I've heard the 904 is better in some respects because of lighter internals, but it's also bad because it has lighter internals that are weaker than its 727 cousin. This will primarily be a street car , but I indefinitely want to be able to put the Sure Grip to use and burn a little rubber. I'm a big kid, sue me. :D

Thoughts? If you say "rebuild it with stronger parts", could you also recommend which parts?

Thanks gals and guys!
 
Well, crap, forgot to put more pertinent info! I haven't gone through the engine yet, but will likely run a mild cam, and have the cylinders bored to the next size as needed. I have NO idea about final horsepower. I think stock was what, like 270-275? I'd like to increase that a bit just for bragging rights, but nothing crazy. I currently have the 3.91 third member, but I'm considering something a little shorter so I get a bit better mileage, more in town / longer drives drivability. If that makes sense.
 
The 727 IS a stronger transmission but your car is light and you don't plan on towing anything around with it so you will be fine. I always thought I needed the 727 but now that I have the car I realize I really don't abuse it as much as I thought I would and a guy I met at a show locally has a 904 behind a built 360 (I believe its stroked) and that car is FAST in my opinion. I asked him if he was worried about breaking the 904 and all he said was that he built the motor expecting the 904 to blow up and when it did he would send it out to get fully built as well... and that after 10 years of driving the crap out of the car, he still hasn't been able to kill the trans...
 
904s will take plenty of abuse if built right. Some drag racing guys build & race them because they're lighter too.
 
niceolddart said:
904s will take plenty of abuse if built right. Some drag racing guys build & race them because they're lighter too.
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That's what I've heard, but I just don't know what "built right" means, as part of me still believes automatic transmissions work on about 10% magic. :)
 
Projectile Dart said:
The 727 IS a stronger transmission but your car is light and you don't plan on towing anything around with it so you will be fine. I always thought I needed the 727 but now that I have the car I realize I really don't abuse it as much as I thought I would and a guy I met at a show locally has a 904 behind a built 360 (I believe its stroked) and that car is FAST in my opinion. I asked him if he was worried about breaking the 904 and all he said was that he built the motor expecting the 904 to blow up and when it did he would send it out to get fully built as well... and that after 10 years of driving the crap out of the car, he still hasn't been able to kill the trans...
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Thanks for that! Yeah, my original 75, back in the early '80s, had a 360 and 727, with the standard rear differential. I did an overhaul once, put it back together, and promptly turned the stock diff into a shiny, shattered paper weight. Had a local shop owner tell me that the 727 was the ONLY way to go, or I would have shredded a 904 too. Maybe it was a status thing? Who knows. But, if I can figure out what I can do to beef up the 904 just a tad, I'm sure that I won't abuse it as much as my much younger self probably did. :)
 
And no, I've got my old truck to tow with, so it'll just be eye candy with a bit of street squealing from time to time.
 
I bought a used "supposedly built" (to what degree I have no idea) A-904 transmission for my Duster back in 2010 for $100, maybe less. First it was behind a roughly 270 HP (crank HP uncorrected at 5000' elevation) 360 for 25k+ miles, then behind my current 360 HP (same, crank HP at 5000') 360 for another 10k miles or so. Most of the time I had it there was no indication the valve body had been modified with a shift kit or anything like that until a few years ago when my valve body cracked and I installed a later one I modified doing a "poor man's shift kit" type deal with the guidance of some super knowledgeable FABO members. Still shifts perfectly and when I pulled the pan to replace the valve body there was minimal clutch material in the bottom of the pan and the fluid looked perfect.

Keep the 904 and just make sure it has some form of shift kit in it to firm up the shifts and reduce overlap between gears when shifting, should last you a long time. The original 904 my Duster came with behind a worn-out 318 did give up the ghost but that was a BONE stock original 1970 transmission that had never been rebuilt and I beat on it pretty hard doing a lot of manual WOT 1-2 upshifts.

I'd personally only use a 727 behind a big block and/or in a heavy vehicle or truck that does a lot of towing and hauling. They're kinda like the Ford C6 or GM TH-400, beefy as hell and last forever (sprag failures notwithstanding lol) but you pay for it with all the power they absorb due to the heavy internals.
 
MopaR&D said:
I bought a used "supposedly built" (to what degree I have no idea) A-904 transmission for my Duster back in 2010 for $100, maybe less. First it was behind a roughly 270 HP (crank HP uncorrected at 5000' elevation) 360 for 25k+ miles, then behind my current 360 HP (same, crank HP at 5000') 360 for another 10k miles or so. Most of the time I had it there was no indication the valve body had been modified with a shift kit or anything like that until a few years ago when my valve body cracked and I installed a later one I modified doing a "poor man's shift kit" type deal. Still shifts perfectly and when I pulled the pan to replace the valve body there was minimal clutch material in the bottom of the pan and the fluid looked perfect.

Keep the 904 and just make sure it has some form of shift kit in it to firm up the shifts and reduce overlap between gears when shifting, should last you a long time. The original 904 my Duster came with behind a worn-out 318 did give up the ghost but that was a BONE stock original 1970 transmission that had never been rebuilt and I beat on it pretty hard doing a lot of "manual" 1-2 upshifts.

I'd personally only use a 727 behind a big block and/or in a heavy vehicle or truck that does a lot of towing and hauling. They're kinda like the Ford C6 or GM TH-400, beefy as hell and last forever (sprag failures notwithstanding lol) but you pay for it with all the power they absorb due to the heavy internals.
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Excellent info, thank you.
 
If you want to do a little searching, you can change the 3 gear planetary to a 4 gear by using an A-995 planetary setup, and also get the benefit of the lower 1st to 2nd gear ratio. You will need the planetary and the matching shaft, I bought mine from a local trans shop for $50. You can also get the stiffer apply lever, either the 3.5 or the 5.0, I think I used the 3.5, the 5.0 was claimed to be a very hard shift. I’m running all 904 behind my small blocks, they are much better IMO for their reduced weight. There is also talk that you can run a 66 trans, which has a front and rear pump, mine was already a 66, but you will need the matching torque converter for the larger front register of your 360, and the offset flex plate. I think you can change the input shaft for the correct spline count, or have the converter built to accommodate that.
 
cosgig said:
If you want to do a little searching, you can change the 3 gear planetary to a 4 gear by using an A-995 planetary setup, and also get the benefit of the lower 1st to 2nd gear ratio. You will need the planetary and the matching shaft, I bought mine from a local trans shop for $50. You can also get the stiffer apply lever, either the 3.5 or the 5.0, I think I used the 3.5, the 5.0 was claimed to be a very hard shift. I’m running all 904 behind my small blocks, they are much better IMO for their reduced weight. There is also talk that you can run a 66 trans, which has a front and rear pump, mine was already a 66, but you will need the matching torque converter for the larger front register of your 360, and the offset flex plate. I think you can change the input shaft for the correct spline count, or have the converter built to accommodate that.
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When you say "66", you mean a 1966 model 904? I already have my 904, but haven't pulled it yet to determine its year. I'd guess 1975, but no real idea.
 
OMG. I need to clean off my boots after reading through all that drivel. Don't touch any TF before 71 or after 78 just to be on the safe side. A 66 doesn't have a rear pump; and you don't want that crap anyway. I would probably tend to keep the 904. What do you mean about the build of the trans when you say that it was a former hole shot car? I'd like to see the guts, but your motor sounds like something a 904 could handle. Thin Red Eagles in the direct drum, Kevlar band; are a couple of cheap upgrades. A cheapo TransGo RV shift kit.
 
If you want to learn all about your transmission and ways to toughen it up you should buy this book, it's excellent and comes highly recommended by several FABOians.

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SA Design SA394 SA Design Chrysler Torqueflite A-904 & A-727 Transmissions: How to Rebuild | Summit Racing
 
I am a 727 man. I'd destroy 904's with Horse power. Just think how long a 904 would last behind a 440 or a Hemi. Probably why they never offered any Big block 904's. If your lacking that much power to turn a 727 keep the 904 and rebuild it more often. Put a 7 1/4 in much lighter also.
 
I've burnt out more 904s in stock daily driving than I can shake a stick at. I've never had a "race" car, put mild cams and 4 bbls on a few but that's about it.
I've swapped 727s in place of 904s whenever there was a 727 available. Problems solved.
318, 2bbl, 2.xx gears even.... And I have not had much luck with 904s. ..
I'd be interested in what you guys mean by "built right" 904. .. most of mine have been assembly line stock.
 
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