727 or 904?

[dart_68]

IMO, if you don't already have a tranny, don't spend money on a SB 727. SB 727s tend to be rarer thus more expensive. SB 904s are pretty much a dime a dozen and will be plenty strong for what you're doing. A 904 weighs less, has less rotating mass, and shifts faster than a 727. Only time I would use a 727 on the street is if I was doing some fairly heavy and frequent towing.

 

[Magster65]

I found this on a couple different sites. It was copied from an old Car Craft magazine article apparently.
(no other info with it)
Powerglide_____18 hp
TH-350________36 hp
TH-400________44 hp
Ford_C-6______55-60 hp
Ford_C-4______28 hp
Ford_FMX______25 hp
Chrysler_A904__25 hp
Chrysler_727___45 hp

The old parasitic drag notion has been around ever since some joker put a 727 from a new Yorker into a Duster. Problem was, he used the New Yorker converter. A lot lower stall than a 904, hence the 'parasitic drag'. Racers run the 904 so they can get every tenth available, but for the street, it isn't worth it. You can actually drop a 904 clutch THROUGH a 727 clutch; there's that much difference in strength. Just a bone stock three clutch direct 727 is twice as strong as a 904. In my 37 years rebuilding them I've only seen one blown sprag; and it was in an old New Yorker being driven by a senior citizen who got stuck in the snow. Hopped up 904's are good for making a ton of money for rebuilders off people who are afraid to cut their driveshaft.

 

[j par]

I would say the 904 has less drag because there's less in it. I'm seriously not joking when I say you can train a monkey to rebuild one of these things.

 

[70aarcuda]

1. the old parasite drag is real...swapped out 727 with TA converter for a 904 with Ta converter...car picked up .15 and 2 mph....some say no big deal...as the car becomes faster...a tenth and half can cost alot of money.....i know big deal you are bracket racing just put a dial in on it and run it.....well..true...but i keep trying new stuff to go faster.
2. As Rob said aka Crackedback....I use stock disc and steel...put 5 of the thin disc and steel in front drum....use the 24 spring kit in front drum..cost about 120 bucks...ATI had the reverse wound big spring for 20 bucks...I have one in 904 but the trans has not made it way into the car it was build for.
3. I replace the servos with billet units from Sonnax ...not very expensive....there is some other billet servos for around 86 bucks.....MOPAR 904 500 42RH 42RE TRANSMISSION BILLET REAR SERVO KIT, DODGE, PLYMOUTH AMC | eBay

For band i use Kelvar lined bands ...some people dont like them....I have never had any problems with them.....they usually sell for around 30 bucks each.........replace drum bushing...pump bushing ...tailshaft bushing....
We have 3 904 in use...they all use Tranzact of Indy transbrake ...I have a complete spare with brake installed...also got another 904 with old TA manual valve body ready for another project this winter....Have used low gear sets and regular gear sets.....only problem i have had is one burned up the clutches in the rear drum a couple of years ago...I have a few problems that were my fault....like rolled lip seal....lol

dont waste you money on bolt in sprag...cause the stock sprag is bolted in....or rivet in....

They are very easy to rebuild as J par says....hell if he can do it...a cave man can do it....

 

[stroked340]

Hopped up 904's are good for making a ton of money for rebuilders off people who are afraid to cut their driveshaft.

And for WINNING at the track..and performing just as well on the street been running mine for SEVEN seasons not one problem with it in my street/strip car worth every dime spent..you can keep those 727's

 

[j par]

 

[Magster65]

I guess it just boils down to preference... both have strong points.
One of the guys in our 'hot rod crowd' had a trans shop for 25 years. I'll work with him but he's the brains (I'll be the monkey in training).
I'll get his opinion too but I'm leaning towards beefing up the 904.

I would say the 904 has less drag because there's less in it. I'm seriously not joking when I say you can train a monkey to rebuild one of these things.

 

[CudaFactHackJob]

People started cussing the 727 when they tried to put them into the 63 66 abodies. They lost patience. Gotta cut the bellhousing floor bumps and notch the trans rib. And the guys who did manage fitting them in used the big converter and usually didn't hook up their kickdown. Shifted it 'manually'. I built my 904 for my 66 with the TransGo shift kit rv heavy duty, with red eagles and 2.74 first, but it's behind a stock 360 and a 7 1/4 rearend. Plus it was in the car already. My magnum 5.9 will be in front of a 727 and 8.8. Some people have good luck with 904's but unless you're racing, you'll be way ahead in the long run with a 727. 904's were only available behind slant sixes when they first came out; for a reason.

 

[stroked340]

People started cussing the 727 when they tried to put them into the 63 66 abodies. They lost patience. Gotta cut the bellhousing floor bumps and notch the trans rib. And the guys who did manage fitting them in used the big converter and usually didn't hook up their kickdown. Shifted it 'manually'. I built my 904 for my 66 with the TransGo shift kit rv heavy duty, with red eagles and 2.74 first, but it's behind a stock 360 and a 7 1/4 rearend. Plus it was in the car already. My magnum 5.9 will be in front of a 727 and 8.8. Some people have good luck with 904's but unless you're racing, you'll be way ahead in the long run with a 727. 904's were only available behind slant sixes when they first came out; for a reason.

Ya,cause' like everything else factory no one knew their true potential..anyone I know and I know a LOT of Mopars guys that race(beat on their cars) all run 904's just need to build them RIGHT like anything else if you want them to last..

 

[CudaFactHackJob]

The difference between a 904 and a 727 is obvious to anybody who has rebuilt both. A 904 clutch will drop thru a 727 clutch. Most guys don't have money to throw away for a tenth of a second and 2mph on a daily driver. If you can find a driveshaft or have one cut reasonably then always choose a 727 over a weak flimsy 904. I build 904's for guys running strokers on the street, but it's not worth it. They have plenty of money but they want it to all bolt together simply. When I talk about driveshafts and cross members, they get a blank look on their face. Too complicated, they say.

 

[crackedback]

Tons of 904's running behind 500hp stuff now. It's not 1970 anymore.

727's blow up, plenty of examples all over the internet and magazines.

Would you happen to be Butch?

 

[CudaFactHackJob]

I see tiny C4's behind 460s too. And if a person wants to win at the track then that's the way to go. A bolt in sprag for a 727 is under a hundred bucks. I hate to see people get sucked into the hype over these weak trannies by these companies trying to make a buck off 904 parts that come stock in a 727. I have plenty of info already in my brain from my own experiences so I am able to stick to the subject at hand. For a daily driver that doesn't need an extra tenth, you're way ahead with a 727. Why take a chance. Eventually it will go out and another rebuild is definite.

 

[CudaFactHackJob]

I'm familiar with the articles on parasitic drag. The numbers are laffable. I see where it's stated that a C6 takes up to 60 horsepower. How can anybody in their right mind believe such nonsense? A VW bug has a total of 60 HP. There's a lot of info on the internet and most of it is bogus, just advertising for somebody trying to make a buck.

 

[stroked340]

I see tiny C4's behind 460s too. And if a person wants to win at the track then that's the way to go. A bolt in sprag for a 727 is under a hundred bucks. I hate to see people get sucked into the hype over these weak trannies by these companies trying to make a buck off 904 parts that come stock in a 727. I have plenty of info already in my brain from my own experiences so I am able to stick to the subject at hand. For a daily driver that doesn't need an extra tenth, you're way ahead with a 727. Why take a chance. Eventually it will go out and another rebuild is definite.

EVERYTHING needs to be rebuilt eventually...weakass tranny far from it you like the 727 good for you but don't put down the 904 just because YOU think they're not any good

 

[j par]

I believe that's the outright beauty of a 904 is how easy it is to rebuild! And look at poor 70aarcuda having to rebuild his after 10 years of drag racing at LOL
Hey "hack job" can you think of an easier auto tranny than the 904 to rebuild? I think it was easier than rebuilding my A833.

 

[CudaFactHackJob]

Not withstanding the childish posts on here, the 904 has its place, but a dependable strong transmission it definitely is NOT. I rebuilt my first 904 in 1980. It was simple; just as simple as a 727. All this hype about how great a 904 is is just rubbish. Anything can be built up if you're working with cubic dollars. A 904 belongs behind a mild small block. If I really wanted to slam a 904 I'd talk about their junk converters that crack because the metal thins out just inside the pump slots. Arguing against a 727 for the street is just sad.

 

[stroked340]

Not withstanding the childish posts on here, the 904 has its place, but a dependable strong transmission it definitely is NOT. I rebuilt my first 904 in 1980. It was simple; just as simple as a 727. All this hype about how great a 904 is is just rubbish. Anything can be built up if you're working with cubic dollars. A 904 belongs behind a mild small block. If I really wanted to slam a 904 I'd talk about their junk converters that crack because the metal thins out just inside the pump slots. Arguing against a 727 for the street is just sad.

Lived just fine behind my 520 h.p. 416..and STILL performing just fine behind my far from stock 360 ..it's all in WHO builds it..and it DON'T take cubic dollars to build a good performing one..if you talking stock converters who uses them

 

[fishy68]

I have a 408 (approx 480 hp) in my 68 Cuda and built a 904 for it 3 yrs. ago. I don't take it to the track much but am real hard on my car. Living out in the country gives many places to open it up. So far it's working just as good as the day I installed it. I wanted to build a trans that lasted a nice long time because my back gives me a lot of pain and R&R'ing them isn't much fun anymore. Here's what I did

1. 73 904 case hot tanked and inspected
2. Steel 4 pinion planetary gearsets front and rear (mandatory with a stroker IMO)
3. Red Eagle clutch plates and Kolene steel plates
4. My trans came with a 4 disc front clutch retainer and I had the local machinist mill the pressure plate down so I could get 5 friction discs and steel plates in it
5. Multi spring pack for the front clutch (you generally don't need this unless you spin it over 6k rpm)
6. New stock type or red lined rear band. Wide front Kevlar lined band
7. Replace all bushings and thrust washers
8. Adjust the rear geartrain end play to .008" or as close as possible. Adjust the front end play to .020" or as close as possible
9. Set rear clutch pack clearance to .030~.040". Set front clutch pack clearance to .060~.075"
10. 4.2 ratio front servo lever
11. Trans-go TF2 shift improver kit
12. Deep oil pan with filter extension. Dacron type filter
13. Good quality transmission cooler

If you machine the front clutch carrier to accept more clutches that the splines on the rear carrier engage into all the front clutch friction discs. Some rear carriers had shorter splines and won't engage all the front discs. One thing that helps extend trans life immensely is the proper installation of the shift improver kit because it boosts line pressure to the clutch packs for more holding power and eliminates shift overlap or flare up.

You might want to check out this book from Tom Hand. It has a lot of great info on building torqueflites

https://www.amazon.com/dp/1613253354/?tag=fabo03-20

I usually buy my major rebuild parts at either www.bulkpart.com or www.wittrans.com
Specialized parts can be bought from A&A trans

 

[crackedback]

Wow...

What's a simple fix on 904's for the cracking converter lug ears? I know of two...

Cubic dollars? Fixing the exploding 727's and rolling sprags is more cubic dollars than you'll spend on a 904 with good parts. 727's explode and roll sprags without expensive front drums and bolt in sprags. Even bolt in sprags get toasted. I've seen at least 10 this year from guys I know. Heck there's a post on moparts right now about a rolled sprag.

BTW, I don't use any fancy clutches or steels in anything I build. A $100 transtar kit an some extra fiber/steels from WIT or bulkpart... done. A good VB and tweak the line pressure a bit helps a lot.

Have at it continuing to belittle those that don't agree with you. It's a good look.

 

[j par]

Hey you know I just threw that hack job comment in just to be funny and lighten things up? But really to come on and say these Transmissions are not dependable and not strong is quite laughable.

Not withstanding the childish posts on here, the 904 has its place, but a dependable strong transmission it definitely is NOT. I rebuilt my first 904 in 1980. It was simple; just as simple as a 727. All this hype about how great a 904 is is just rubbish. Anything can be built up if you're working with cubic dollars. A 904 belongs behind a mild small block. If I really wanted to slam a 904 I'd talk about their junk converters that crack because the metal thins out just inside the pump slots. Arguing against a 727 for the street is just sad.

 

[Coffee&Cars]

Yes the 904 is quicker, about a tenth. However, it is small and has weaker parts because of it's physical size. It takes a little more to give it the strength the 727 already has. More and larger clutches gives more surface area for grip. If you do it right you can stuff "6" clutches and steels into a 727. Alum. forward drum will make your 727 spin faster, billet drum will make it stronger. 4-5 pinion carrier a must. Use the best bolt in sprag you can get. This combo will take a lot of power. There are a torrid of causes that can cause it to blow up! Not just the above mentioned parts. Install a safety device!!!!!! Why? Insurance company's are not going to cover you for a racing accident. Protection costs less than hospital bills !!!!!!!!!

 

[CudaFactHackJob]

I know how frustrating it can be to find answers sometimes. That's why I pay close attention to the facts stated by the original poster. He said he has both 904 and 727s. He also said his transmission mechanic isn't that familiar with building high performance transmissions. He said he wanted advice on building a 904. I promote the 727 and I get clobbered by 904 fans but they can't seem to give this guy any pertinent advice. I guess they don't really know much about the actual inner workings of a hyper 904. If they did, the first thing they would suggest is a five plate direct drum which takes a wider band as well. Then red eagle clutches; all forward thins; six into the direct drum. Kevlar band. Very minimum of endplay measured on a cold case. Anything added to this grocery list would be welcomed by all I'm sure.

 

[dart_68]

I know how frustrating it can be to find answers sometimes. That's why I pay close attention to the facts stated by the original poster. He said he has both 904 and 727s. He also said his transmission mechanic isn't that familiar with building high performance transmissions. He said he wanted advice on building a 904. I promote the 727 and I get clobbered by 904 fans but they can't seem to give this guy any pertinent advice. I guess they don't really know much about the actual inner workings of a hyper 904. If they did, the first thing they would suggest is a five plate direct drum which takes a wider band as well. Then red eagle clutches; all forward thins; six into the direct drum. Kevlar band. Very minimum of endplay measured on a cold case. Anything added to this grocery list would be welcomed by all I'm sure.

I think I missed the post about that he has both. In that case, I would go with whatever would be easiest and least expensive. If he has a drive shaft that specifically fits a 904 or 727 then I would build that tranny. The 727 is definitely beefier out of the box but not always necessary.

 

[Magster65]

People are passionate about their beliefs! It's all good CFHJ. Thanks for the input. I'll take this entire thread with me when I meet up with my trans guy this week.
Cheers

I know how frustrating it can be to find answers sometimes. That's why I pay close attention to the facts stated by the original poster. He said he has both 904 and 727s. He also said his transmission mechanic isn't that familiar with building high performance transmissions. He said he wanted advice on building a 904. I promote the 727 and I get clobbered by 904 fans but they can't seem to give this guy any pertinent advice. I guess they don't really know much about the actual inner workings of a hyper 904. If they did, the first thing they would suggest is a five plate direct drum which takes a wider band as well. Then red eagle clutches; all forward thins; six into the direct drum. Kevlar band. Very minimum of endplay measured on a cold case. Anything added to this grocery list would be welcomed by all I'm sure.

I only have the tiny little slant 6 driveshaft but my bro has a wrecker just down the street... there'll be something in there I can use to make one.
I have a feeling my trans guy is gonna say stick with the 727... thanks for your input.
Cheers

I think I missed the post about that he has both. In that case, I would go with whatever would be easiest and least expensive. If he has a drive shaft that specifically fits a 904 or 727 then I would build that tranny. The 727 is definitely beefier out of the box but not always necessary.

 

[Magster65]

Thanks everyone, I think there's enough info in this thread to move forward.
I appreciate everyone's thoughts.
Cheers