Transmisison 904 vs. 727

-
G

gold75duster

Member
Joined
Mar 28, 2010
Messages
11
Reaction score
0
Hi Everybody,

I have a 75 Duster with a stock 318 and automatic tranny.

I recently discovered that the 318 has compression in all of 5 cylinders and could realy use a rebuild.

I am in the process of pricing out having a modified 360 built for it but am concerned with the rest of the drive train. Engine will have a moderate cam, edelbrock heads, edelbrock intake and carb.

I have the broadcast sheet and it lists the transmisison code as D34 in line 2 (automatic) and 423 in line 4. I have looked on line an can't determine what transmisison it is but it looks like 75's came with the 904?

Will a stock 35 year old transmission expolde if I put the power of a 360 though it (assuming it produces approx 350 HP)? Any ideas on what sort of power these transmissions can take would be helpful.

Should I be looking at having a sturdier transmission installed or rebuilding the existing one? Any idea on ball park figures for a reman tranny would be appreciated.

Also, will a 8.25" rear end be sufficient? I am planning on having the rear end done as it is making noise and want to put some shorter gears in it.

Any advice . thought would be greatly appreciated.

Thanks
 
It is pretty typical for the 318 to be paired with the 904. It's a decent tranny and should be able to handle 350 hp. Suggest making sure it's not worn out. If you decide to keep it, I recommend putting a RV shift kit in it. FWIW, I have a warmed up 318 in the Demon with a 904. The 904 has a TransGo RV shift kit in it. A competition kit is available, but the Demon is street car.

The 8¼ is ok as rears go. Mopar put 'em on 360 Magnum Dakotas. Putting a locking differential on it spreads the torque load and reduces the chances for snapped axle shafts. I haven't heard anything near the noise about 8¼ that I've heard about 7¼.

Price for services is going to be all over the place. Best to look for quality service first, then price. There are lots of horror stories on here from people who tried to do something on the cheap and got burned badly. It usually costs less to do it right the first time.
 
Gold75, I think your 8 1/4 is integral 3rd. member? If you decide to up-grade to 8 3/4 or 8"/9" ford,with removable 3rd. member, their easier to service(on the bench).Easy to exchange for say drag or track day use. If you decide to up-grade to an auto with o.d.,would be like best of both worlds, lots of rear end ratio and good cruise rpm. Good Luck, ateam.:cheers:
 
Gold75, I think your 8 1/4 is integral 3rd. member? If you decide to up-grade to 8 3/4 or 8"/9" ford,with removable 3rd. member, their easier to service(on the bench).Easy to exchange for say drag or track day use. If you decide to up-grade to an auto with o.d.,would be like best of both worlds, lots of rear end ratio and good cruise rpm. Good Luck, ateam.
 
Nothing wrong with a 904. A 727 is naturally stonger because it has bigger (but heavier) parts in it. I use a 904 and there are lots of race 904's used behind big blocks (in 727 cases and w/adapters) and some other very fast cars. It just depends how much you want to spend. But there is nothing really "trick" with the JW Trans. 904 I have.

A rebuild would be in order with a good shift kit or valve body. Red clutches are suppose to be better than the blue ones. (forgot brands) An external trans cooler will help overall life.

This is a 727. It has an area that sticks out under the dipstick tube.
http://image.fourwheeler.com/f/9192010/129_0608_10_z+automatic_transmission+torqueflite_727.jpg
A 904 has a pretty much square pan.
 
engineers do a great job of finding a happy medium.Such as 318/904/8.25 When you decide to upgrade one whether you like it or not you will upgrade the others.350 h/p is about twice what your car came out with.904 is a great transmission and will hold up with upgrades also.8.25 kind of iffy.I have seen too many of them broke to say they hold up.
 
You'll be just fine with the 904 give it a good rebuild with quality parts and it'll handle 350 h.p. no problem my 904 has been behind a 520 h.p. 416 and is currently behind my 406 h.p. 360 and has taken a beating at the track for 4 seasons and is still holding up..
 
If you never want to do the work again..go the 727/8 3/4. Draggers race with the 727..and they are tough..for cruising, you would no know the difference...AND you can get a very good overdrive for under 100 bucks..

Grassy
 
You can beef the 904 pretty tuff and many guys even put 500+ pHP in front and run 10s so it should be just fine!

Build it tight, good clutches, new steels and all new seals, solid bands not flex , 4.2 lever for 2nd a tf2 shift kit and maybe billet servros and a bolt in sprag buddy. Will be bullet proof.. enjoy:)
 
The A-999 is a bad boy. It has a 5 clutch direct drum and a four clutch forward drum and 4 pinion planetaries and a lower gearset than the 904.....that is, if you can find one. If not, then the 904 can be upgraded easily. Some people don't like the extra low gearset in the A-999, but I kinda like it on a street car. If you find an A-999, or mod one like an A-999 and use good parts like a good quality reprogramming kit (I like Transgo), Red Eagle clutches and kevlar bands, it will hold 500 HP. Bucky Hess used to run a highly modified 904 behind a Hemi in his SS/AA '68 Barracuda. That car went like 8 seconds with a 904. Needless to say it was well past 500 HP. Course, he had stuff like billet drums and whatnot that REALLY cost. An expense you really don't need at 500 and under HP. I've also witnessed first hand the difference on the dyno as a part of test we did years ago on parasitic drag. We made several dyno runs between the two (727 and 904) and found the 904 on average used 60 HP less than the 727. That's a gob of HP gettin to the rear tires by just a transmission change. To me, it doesn't make sense NOT to use a 904 of some sort. It's a no brainer as they say. Here's my A-999 with some clues on how to tell one when you see it:

A-999-1.jpg


Hope that helps.
 
60 hp loss at the rear wheels is significant..and very hard to believe...why do most mopars use the 727 or has this changed as well ? ..or are the folks that I know that are MOPAR are too old school ? All these changes are hard to keep up..

Should we all be running 8 1/4s as well ?

Grassy
 
Everyone i know runs a 904 in their a-body..and they all race and beat on them and they last...:D:D
 
grassy said:
60 hp loss at the rear wheels is significant..and very hard to believe...why do most mopars use the 727 or has this changed as well ? ..or are the folks that I know that are MOPAR are too old school ? All these changes are hard to keep up..

Should we all be running 8 1/4s as well ?

Grassy
Click to expand...

Simply because the 727 was touted as the heavy dutier of the two....and it is. but with modern technology and the introduction of the A-999, the anti got upped on the 904. The HP loss isn't hard to believe when you have a 904 and 727 torn down on the bench together. The difference becomes apparent then. ...and no, the 8.750 is still the weapon of choice as far as I'm concerned.
 
I,m running a built 904 behind over 500hp,ran [email protected],s much lighter than the 727 and built right can do the job easy.Must be years of tinkering with the 904,they,ve found a way to run better than the 727,s.
 
why do most mopars use the 727 or has this changed as well ?
Click to expand...

because they are living in the stone ages and listening to 20 year old magazines and oldheads.. its the same as the guys telling you that anything over 3000 stahl is too much for the street. all my friends are running 904s in their small blocks.. took some time to convert some of them but they are now believers...
 
I was told by another member,that I was wasting/copying people with more money than brains by building a 904 for racing.Prove me wrong now?My total cost for my rebuilt 904 racing tranny was $750,which I thought was rather cheap for a race built tranny.
 
So the 904 is what behind my /6 ? So I could just pull out the /6 and drop in the 360 and all would be good ?

I have heard that about the stall as well...

Grassy
 
torquehouse said:
Your /six 904 bellhousing bolt pattern is different than a small block 904. But internally, they're basically the same.
Click to expand...


904 comes behind /6 has 3 clutches in forward clutch pac
998-------------318..... 4
999..................360.... 5
 
grassy said:
..so in theory, if I have an adapter plate , I can do this ?

Grassy
Click to expand...
Hold on Grassy:small block 904s are easy to get ahold of.Adapter plates are not cheap.I think i have 5 in my barn.Come and get one.
 
d5667,

Thanks for the offer but MO is a long way from where I live :) . I will poke around here to find one..Thanks. Ian.
 
You must log in or register to reply here.
-

Back
Top