Ok I just went through 904 h*ll trying to match parts together. Let me share my story. . .

A long time ago, in a land far away. .. (ok it was only 6 years ago) I had a duster, that I wanted to put a 904 in. High 11 sec 340. nothing too special. From day one, the 904 gave me problems. The trans would flare the 2~3 shift, but only if I really wound it up (say over 6,000 rpm) To make a long story short, I replaced the following parts in no particular order. Valve body, pump/stator, high gear drum, input shaft/rear drum/ clutches/steels/bands/2nd gear servo/ int. band lever/ etc. . .basically every part in the trans. I finally gave up and put a 727 back in it. Well 6 years have passed, I have coleen steels, raybestos blue plate special race clutches, and an $800 turbo action converter, that I just can't give up on. So I decided to jump back in for my 416" EFI duster I'm doing right now.

At the time, I called every trans shop in the country. Nobody could figure out what it was. So this time, I really spent a lot of time trying to figure out what it was myself.

Well at the time when I put the trans together, in my infinate wisdom (I was only 20 by the way), I decided to put 5 rear (thin) clutches in my 4 clutch high gear drum. I'd seen this in pro trans' and other race type stuff, so I machined down my pressure plate, and made it all work. Now upon close inspection this time, I realized that the bottom clutch of the high gear clutch pack, was borderline to engagement on the rear clutch splines. What I figured out was happening, is that at low RPM, as the piston moved in the high gear clutch to clamp the clutchpack, even when the bottom clutch wasn't splined (indexed), it would simply rotate in to place and apply. But at high RPM the bottom clutch was spinning so fast, that it just kept skipping over the teeth on the rear clutch. Since it wouldn't spline itself, being the bottom clutch, it kept the entire clutch pack from clamping, thus causing the flare, until the point that the force of the piston caused the clutch to finally engage into high gear.

So because of all that, I have spent a lot of time looking and understanding the seemingly millions of 904 variations there are out there.

Here are a few things I've learned.


Any 4 clutch drum, will fit any 2 ring pump, as long as it is not a machined 5 clutch high gear drum pump, then there is potential for problem.

5 clutch drums will only fit machined
(clearanced) pumps.

If you plan on using a 5 clutch drum, you must have the correct rear clutch/input shaft to go with it. (this goes for 4 clutch stuff too, there are 3 clutch pack "colt" style stuff so pay attention!) If you don't use the matched rear drum/front drum the splines on the rear drum, will not completely engage the bottom clutch on the high gear drum.

Non lock up input shafts, CAN NOT simply be pressed into the mating rear clutch for a 5 clutch high gear drum. So if you're thinking of pressing out the input shaft of a non-lock up drum, to press into the lock up rear drum, you can't do it. The reason is, the snap ring location between the 2 are different. If you put the non-lock up input shaft, into the lock up style rear drum, it could move around .060. Which means the endplay could also move that much.)

From what I can tell there is only 1 input shaft/rear drum combo that will work to make a true non-lock up 5 clutch high gear drum combo work. It is a non-lock up 3 ring style, which uses a completely different pump all together.

There are several different high gear drums. Some even have different diameters which necessitates a different sun shell. There are 1 and 2 bushing types. There are also 2 different diameter stator supports. They only vary by about .050, so you have to really pay attention. The high gear clutch must match the pump/stator diameter.

Low gear sets can be switched out of late style 904's. but the thrust plate that go between the snap ring, and the sun shell must stay with sun gear. There are at least 2 distictly different thickness thrust plates in the sun shells.

You have to be very careful mis-matching parts together. The sealing ring heights on the different stack ups, can vary by as little as .100" from one style to the next. So what looks like it may work with no problem, if you have the end play set loose, it could cause some huge problems.


My advice to anyone that wants to run a 904 is to stick with an early style 4 clutch. The newer you get, the more variations and suttle changes there are. The low gear set can be simply swapped into your trans (78 and later 904/998/999 trans have 2.74/1.58 gear sets) Just make sure you take the sun gear/thrust plates/spacer/planetary's and thrust washers as you will need all of those parts to do the swap. The 904 will hold a lot of power. Their light weight/small design vs. the 727 gives it a significant performance advantage on the right application. Just make sure you be careful when you start swapping parts because they aren't as forgiving as a 727 when it comes to part/year swaps.

Anyway. I hope all of my pain and time can be useful to someone out there.

Good stuff man ! thanks for taking the time to post all that. Just in time.I might be doing a 904 for my cuz...

Thank you for all the info

if I was home I could give some more tid bit's on the 904's, including picture's, clearances and such, look for additional info sometime in the morning.

I went thru this same scenario back in 1995. I had a 1973 904 that came behind a 318. I wanted to swap in the 2.74 low gear and the wide 5 clutch drum. Doing a lot of research, there were several different variables that had to match before parts worked together. The best core to start with was the 1975-1977 A999 trans that came behind 360 engines. These had the wide 5 clutch front drum, non-lock-up shaft, bevelled back pump, and longer splined forward clutch drum hub. If you could find one of these, all you needed was a 1980-up 2.74 gear set to complete the package. I could not find one, so I started piece parting this thing. I was able to obtain a bevelled back pump & a wide 5 clutch direct drum from a local tranny parts house. These were for a '75-'77 360 trans. I still needed a special bevelled direct clutch drum piston and the longer splined forward drum with non-lock-up input shaft. I got the P/N for the dished piston in the Direct Connection Chassis Book, and the Mopar dealer ordered one. No luck finding the forward drum, so I called Dynamic Racing trans. They knew exactly what I needed, and sent me one. The forward drum used with the 4 clutch direct drum has a 1" splined hub, but the forward drum used with a wide 5 clutch direct drum has an 1-1/8" splined hub. This is the difference that was pointed out at the start of this post. After all the parts were obtained, the trans went together without problems, and still is being run in my low 11 sec 340 Duster. I wanted to build a spare trans, but had problems finding the '75-'77 parts. So I did some more research and calls. Found out that the '78-up parts will work, if I can find non-lock-up components. So, off to the tranny parts house. Was able to find a non-lock-up, bevelled back pump, wide direct drum, and the non-lock-up long clutch hub forward drum. The '78-up parts used a slightly different sized sealing ring on the stator and forward drum, ~0.060", so you have to be careful when matching parts. The non-lock-up pump has 2 balls sealing passages in the stator and the lock-up has 3 balls. That is an easy way to ID them. The '78-up parts seem to be more plentiful, but usually you find lock-ups in everything from '78-up except for Fleet vehicles, trucks, etc. I have an old CarMatic trans parts book as well as one from Delta that I use to ID parts. It gives Mopar part numbers as well as industry part numbers, and some identifying dimensions where required. The 904 is a challenge to build with all the variations, but as long as you have all the info, it becomes an easy task. I talked to Rick Allison at A&A for 2 hours, and he helped me tremendously.

John

I have an '86 998/999 that I'm parting out (valve body is sold). it's a 2.74/1.54, 5 disc clutch lockup tranny. what would be the parts to keep that people might be interested in before I take the rest to the scrap yard? the suns,planets, and associated thrust washers? drums, too?

Here are a few pic's of mod's that can be done to a 904, these are from mine when I built it and using a trans brake. The first one is a sleeve that I used to replace the govenor, since it is manusl shift only, you don't need it.

this is the drilling for the transbrake wiring connector.

this one show's the sun shell after I lightened it.

this one show's big spring that the multi spring retainer replaces, the multi spring retainer is a good investment as it helps with the flare up problem that is common in 904's created by the large spring coming unwound at high rpm's, found this out by talking to Rick Allison a A@A

this show's the oil escape hole's in a front drum, so the plates won't hydraulic.

here are some of the part's that went into mine,selective snap ring kit,4.2 lever and renforced band strut.

oiling mod to the stator support, plus the use of the teflon sealing ring's make a big improvement

with a few exception's the 904 to me is the same as the 727 except smaller, and anything you can do to improve a 727 will work for a 904 also, the best thing to have is a manual and the ATSM is a good one and the Torqueflite handbook is another.

Patrick - the entire 2.74 planetary geartrain including sun shell, which is unique to the 2.74 set; The wide 5 clutch drum, the forward drum with shaft - the shaft can be replaced with a '78-up non-lock-up shaft; the pump can be reused in a non-lock-up application if one of the balls in the stator is removed. It is kinda tricky to remove, but can be done. The front servo is a controlled load and is not desirable. The low/rev drum is not special. John

thanks, if i ever build my 66cuda w/ a small block it will have a 904

If you do the oiling mod to your high gear drum it doesn't hurt to drill a row of extra holes in the band as well to vent the extra oil. One other thing I've noticed is that the 999 seems to have a heavier duty [ thicker ] drive shell than the 904 so if you're looking to lighten a drive shell maybe start off with the lighter one.