727 -> 904

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alfred340

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I have the possibility to buy a ´79 A-904 with TCI pan and TCI 2600(?) stall converter. Bands and clutches are worn, as I was told its driveable but would rev when braking. I´d go through the internals anyway...
I think about installing it instead of my badly leaking 727. Car is a ´68 340 Cuda with 8 3/4 rear.
What would be the mayor issues in the swap? Can the driveshaft be lengthened or woukd i have to buy a new one? What about crossmember and linkage?

Greetings from hot Bavaria
 
The linkage may not be a problem, the driveshaft will be about 1 1/2 inches to short, so you'll have to get another one (I don't think they can lengthen a drivshaft, but I have never worked in a driveshaft shop). Also, you may need to get a new flexplate as the 727 plate may be bigger. One the bright side, you should start putting down about 30 more HP to the ground with the 904 as it has less rotating mass.
 
30 horsepower? No way. A maximum of maybe, and I mean maybe with everything else maxed out, 18.

I don't think the swap is worth it unless you are running a stocker or a super stocker where every hundreth of a second may count. I run a 904 in my car because I went from a 4 speed to the automatic. The price differential was negligable since I had to buy everything anyway. To put a 5 disc front clutch in a non lockup 904 requires a list of specific parts that were only produced for a few years and aren't always readily available and I know they aren't available new from Mopar. So the reliability and ease of parts procurement is just not as good as it is with the 727. Besides what are really after, the absolute best ET or dead nuts reliability with a little (hardly even noticable) less performance?
 
I agree with Guitar. Rebuild your 727 and stay with reliability. Yes the 727 will use a little more HP to turn it but it's worth it in reliability. As far as how much HP difference there is. I read an article a few yrs. ago that did comparison of all the major manufacturers different automatics and how much HP they required to turn them. The 904 required 42 hp and the 727 took 55 hp so there was only 13 hp difference.
 
I´d have to update the 727 anyway. And the 904 comes with pan and converter which alone would be over $500 in Germany. I´d buy the whole thing for $300 plus ~$150 for a clutch and gasket set.
As I heard, lengthening and balancing the driveshaft would be around $150.
The 727´s stock converter is already stretched to its limit with my XE268H cam. I think the 2400 stall TCI would be just what I need to keep it streetable with some reserves to go one step further. But I´m not that experienced with converter stuff. Still trialin´and errorin´. :blackeye:
 
BTW, reliability isn´t the big issue. With our gas prices being $6.50 per gallon, the car won´t be driven more than 1000mls a year. :sad1:
Unbolting and bolting stuff is the most economic way to have fun with the car. :)
 
I understand where your coming from. But I think if you figure up things the cost will be close no matter which trans you choose. You say the 904 will cost you $300 plus need rebuilding adding $150 plus needing driveshaft work adding another $150. That brings the total to around $600. Add $50 for flushing the torque converter cause any torque converter should be flushed out if the trans. has been burned up that it was in. Now your at $650. Stay with your 727 and rebuild it ($150 for a kit cause they cost about the same as a 904) and put in a new converter and deep pan (you said $500 for them) and your at $650. Same price and in the end you still have a new trans with a stall speed converter and deep pan and it's the heavier duty 727.

Don't get me wrong I'm not trying to make up your mind for you. Just giving you something else to think about.
 
Well not only will the driveshaft need to be retubed you'll be buying new u joints and a slip yoke as well. The dipstick tube is not the same either. The linkage and arms maybe OK but the flex plate is probably different as well. It's not as simple as it sounds. Rebuilding your 727 and buying a converter for it are better options. The pan is just icing on the cake, makes it sweeter but is not needed.
 
I must admit you´re probably right. The smaller tranny wouldn´t be worth the fuzz.
What about the Mopar performance converters like the 166K P4876878. They tend to be less pricey than aftermarket pieces and should offer the bit of extra stall I´d like to have. Are they ok in terms of quality and performance?
 
We put one in a friends car and he hasn't had any problems with it. I think it's just a stock converter with some extra stall speed in it. Don't expect it to have any torrington bearings, a steel stator and/or furnaced brazed turbine fins.
 
I swapped from a 727 to a 904 last year. The only things I had to change besides the Tranny/Converter were the drive shaft and U joints and slip yoke. I am using an aftermarket shifter though. Dip stick tube from the 727 worked fine.

Ive been told anywere from 15 to 30 horse power less to turn a 904 over the 727 wicj is 1.5 to 3 tenths in the quarter.
 
Two friends of mine, one runs a B/SA 440 6 pack Challenger and the other runs a FA/SS 440 6 pack Challenger both bought the $5000 whiz bang Pro Trans 727 with 904 guts trannies for their cars and only picked up .15. How this would be worth it for a street car or a bracket racer is beyond my comprehension.
 
understandable but were not talking $5000 protrans. If his tranny needs a rebuild anyways and he can get the 904 with the converter and good pan he's pretty much gaining the extra power for nothing. A 904 will handle a mild small block without any problems.
 
I'm also running the 166K Mopar perf torque converter due to cost restraints. Seems to work ok so far but I haven't ran it much yet. I have a buddy who has ran several with no problems and some of his cars have made over 400 hp. I did some checking and Guitar is right. They're just stock converters that they modify for more stall. But they're cheap. If you just have a mild build they should suit you fine.
 
AdamR said:
understandable but were not talking $5000 protrans. If his tranny needs a rebuild anyways and he can get the 904 with the converter and good pan he's pretty much gaining the extra power for nothing. A 904 will handle a mild small block without any problems.
Click to expand...

I think you missed my point, if a $5000 transmission only picked their cars up by .15 how much do you really think a stock 904 is going to do?

The Pro Trans transmissions have all the lightest aluminum internals with roller bearings and Torrington bearings. They are the lowest drag 3 speed TorqueFlites that you can buy and that .15 is all they do.
 
John Cope of CRT told me that the roller bearings and light internals gain durability thing then power. From what I have heard is most people who have switch from a 727 to a 904 pick up anyweres from a tenth and a half to 3 tenths in the quarter. So 15 to 30 hp. But that is just what I have been told not from experience.
 
I've always heard the same thing as well but how accurate is that? My car may pickup 2 tenths from one weekend to the next just from the difference in the air. I think it's way optimistic to expect even .15 from a stock 904 from a 727. You may see some improvement from a small cubic inch low torque engine but I really doubt there's a verifiable tenth of a difference. Heck you can get that or more just from a converter change and we all know the same converter wasn't used in both transmissions. What I think is an advantage in the 904 is the available (relatively) cheap factory low gear set and it's lighter weight. If not for that I don't see the point.
 
I agree with Guitar.

The 904 advantage is in the low - cost low gear set, and a little less rotating mass, but on the street -- I would take the 727.

I have a 1971 Duster 340 that currently has a 904, and I just sold a 1969 340 Dart Swinger with a 727.

Looking at the 727 on the bench with the factory service manual, the 727 has much more surface area in areas known to take stress, clutch packs look different on the 727, bigger beefier parts overall.

The 904 looks OK, but I see no real performance gains with the 904 over the 727 at the strip.

Always keep in mind that the torque converter has a LOT to do with overall performance (stall speed, flash, etc.).

For my money give me the 727...
 
You can have the 727, I'll stick with my 2.74:1 first gear, 1.54:1 second gear A904. Very very happy with how it performs.
 
Interesting. When I was first building my car and planning to use a 727 behind my 360, all I heard was "don't use the 727, use the 904, it will be better all the way around".
I had never had any luck with 904's holding up on the street, but I went ahead and got a core and built the 904. I still have my small block 727 core, the 904 is holding up okay for now, but if it goes the 727 is going in there.
 
ANY good build on a 904 will hold up to anything you can throw at it...

I have a friend, that is running a locally built 904, dynamic converter and has it in the mid 11's 11.53 to be exact. he has had the trans in the car for over 5-6 years, 4.56 gears, wheelstands, anything he throws at it it handles, over 1000 passes, and NO PROBLEMS...

you guys are goofy thinking that you need a 727 for the street..... plain and simple.

you WILL gain at least a .10 on the track from the swap.

do you know they make adapters for big blocks so they can run 904's?

do you know that they take 904 internals and put them in 727 cases for ULTRA high performance builds?

there is no way i'll ever put a 727 behind a small block, street or strip.

if you want to , go ahead, I am not stopping youi but please keep your facts correct. the 904 WILL handle anything this aforementioned car can throw at it.
 
i don't know. i have been running a 904 in my car with no problems. and i beat the ever living crap out of it... i think the reliability arguement is just an old school way of thinking to me... if you build them with quality parts and know what your doing they will be fine... guess everyone has their opinion but i will never put a 727 behind a small block.. 904 all the way for me..


in your case if money is an issue and you have everything for the 727 it may be cheaper to keep the 727 instaed of getting a longer drive shaft and new flexplate.. the linkage shoud be the same between them..
 
It's the same arguement for a lot of stuff.

People would all say a GM 12 bolt was the only way to go, and that 10 bolts sucked. Then the 12 bolts started to dry up...suddenly the parts are available for the 10 bolts and they take the power.

Same with Ford 9" vs. the 8.8"

Same with our 8.75" vs 8.25"

Granted, there is a limit to what an 8.8 or 8.25 can take, but it's alot more than many of us are running in our cars. I'm sticking with both my 904 and my 8.25.
 
Any tranny can be built quite a bit stronger than original,but the big boys will always be tougher because of there size.The 727 is the big brother to the 904, as the T400 to theT350, or C6to the C4. YES, bigger is better, just maybe not as quick.Ive built lots of trans and I couldnt be bothered with a small trans.
 
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