Beefing Up 904

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Topless69

Topless69

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I know this has been discussed often here on FABO, but I also know tech, means and methods and parts selection are updated regularly, so here goes…
I’m replacing my original 318 with a 340, and while it’s out, I’m taking my stock 904 to a shop for rebuild/strength updates.
Any suggestions, advice and help you guys could offer would be greatly appreciated, since I know next to nothing about automatics and they’ve always been something of a black art to me.
Whatever brands, parts, advantages, disadvantages and pitfalls recommended will be studied, researched, pored over and implemented with great care, as I only want to do this once.

Thanks in advance to all the FABO tranny gurus and everyone else on this great forum for all the help and advice in this project!
 
/6 first gear, steel 4 pinion planetaries, kolene steels, good mancini clutches, good kevlar bands. That's how my 2 904's are built for drag racing.
 
Topless69 said:
I know this has been discussed often here on FABO, but I also know tech, means and methods and parts selection are updated regularly, so here goes…
I’m replacing my original 318 with a 340, and while it’s out, I’m taking my stock 904 to a shop for rebuild/strength updates.
Any suggestions, advice and help you guys could offer would be greatly appreciated, since I know next to nothing about automatics and they’ve always been something of a black art to me.
Whatever brands, parts, advantages, disadvantages and pitfalls recommended will be studied, researched, pored over and implemented with great care, as I only want to do this once.

Thanks in advance to all the FABO tranny gurus and everyone else on this great forum for all the help and advice in this project!
Click to expand...

After doing the same research while my old 273 was out and I was waiting for my BPE 408 to arrive, I had a parts list $1800 deep and sill hadn't picked out a converter or found someone to do the buildup confidently.
Then I went to the TCI website and saw that for around $2k I could get a new Streetfighter 904 good for 400 HP.
StreetFighter Transmission Package Torqueflite 904 1967-79 (318, 340, 360) Converter #141300 Non Lock-Up
When it came I put it all together and now with about 2500 miles and quite a few hard acceleration events; I am very happy with my choice.
Something to think about...

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Vince, I hope you have better luck than a lot of us have had with TCI. I'm not dissing your purchase, but I along with others have had no GOOD luck with TCI transmissions. I hope they have upped their QC & are turning out better merchandise now.
 
904s have too many limitations to get them to handle 400hp. Maybe start with a 999 and build it retro...There are too many people making money off C4 and 904 transmissions and they keep up the hype that they can be built to handle 900 hp etc, but we're talking $4-5k for a real one, not something with a couple sets of reds and a kevlar band with billet servo...Anybody who has compared a 904 to a 727 and a C4 to a C6 would have an understanding of the differences between a money pit weakling and a stock trans capable of 400 hp.
 
CudaFactHackJob said:
Step #1...take your transmission to a shop that doesn't need you to tell them how to build it.
Click to expand...
This is the best advice EVER! So go ask around your area for a competent trans shop for older cars. Try the drag racers first, they know people.
 
413 said:
This is the best advice EVER! So go ask around your area for a competent trans shop for older cars. Try the drag racers first, they know people.
Click to expand...
Scrap it and put in a 727.

On the TCI thing I have never spent any money on TCI anything but see a couple of their converters available for what seems like a decent price, compared to a stock reman. How are their converters? Decent or crap?

My converter seems to work ok driving, but I think that my ring gear has issues listening to how it spins over on the starter. I'll know when I swap engines. (That will be happening no matter what)
One of those "as long as it will be exposed and staring me in the face" kind of things.
 
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Depends on what you are going to do with it, and how powerful the engine is. If it is fairly stock engine, for the street, I would recommend a manual valve body, deep trans pan and increase the high gear clutches and change the spring in the drum , rebuild with good parts. The AMX I drive has a Torque Command transmission, AMC's version of a 904. It has gone 9.90s in the 1/4 mile at 3200 lbs. Before last freshening, had over 300 runs. The last 904 I built, I had over $1000 in parts, and already had the low gear set, valve body and deep pan.
 
I used transgo s shift kit on my 904 that made a hell of a difference, really fast hard shifts that chirp me into another dimension
 
CudaFactHackJob said:
904s have too many limitations to get them to handle 400hp. Maybe start with a 999 and build it retro...There are too many people making money off C4 and 904 transmissions and they keep up the hype that they can be built to handle 900 hp etc, but we're talking $4-5k for a real one, not something with a couple sets of reds and a kevlar band with billet servo...Anybody who has compared a 904 to a 727 and a C4 to a C6 would have an understanding of the differences between a money pit weakling and a stock trans capable of 400 hp.
Click to expand...
 
904 and 999 are teh same basic trans, a few little differences within, but not much
 
Math is hard for some people; but geometry is impossible. If you take the time to measure a 904 and a 727 clutch disc do the math, subtract the difference, You'll find that the 904 plate is a little over HALF the friction area of a 727; exactly only 5/8 the area. A six plate direct clutch 904 is 75 square inches of friction material. A six plate 727 is at 118 square inches. A four plate 727 is 79 square inches; a little bit more than a six plate 904. To get to six plates in a 904 it requires a lock up trans as a foundation for parts. And then you need a dummy lockup converter..more expense. A lot of trouble to get to a point that is still weaker than a stock 727. And for what? 1/8 of a second in a quarter mile? The friction material in a 904 has an outer radius that is smaller than the inner radius of a 727. You can easily drop a 904 plate right thru a 727 plate. Consider the difference in the leverage a 727 plate has since the radius is a lot larger. There's more to strength than square inches; it depends on how close to center those inches are. Based on square inches plus leverage, a 727 plate is over twice as strong as a 904 plate.
 
CudaFactHackJob said:
Math is hard for some people; but geometry is impossible. If you take the time to measure a 904 and a 727 clutch disc do the math, subtract the difference, You'll find that the 904 plate is a little over HALF the friction area of a 727; exactly only 5/8 the area. A six plate direct clutch 904 is 75 square inches of friction material. A six plate 727 is at 118 square inches. A four plate 727 is 79 square inches; a little bit more than a six plate 904. To get to six plates in a 904 it requires a lock up trans as a foundation for parts. And then you need a dummy lockup converter..more expense. A lot of trouble to get to a point that is still weaker than a stock 727. And for what? 1/8 of a second in a quarter mile? The friction material in a 904 has an outer radius that is smaller than the inner radius of a 727. You can easily drop a 904 plate right thru a 727 plate. Consider the difference in the leverage a 727 plate has since the radius is a lot larger. There's more to strength than square inches; it depends on how close to center those inches are. Based on square inches plus leverage, a 727 plate is over twice as strong as a 904 plate.
Click to expand...
The point of my posting that link was to show that there were key differences that Chrysler made to the 999 version to make it strong and durable enough for small block v8 use. The 727 is overkill for a small block. Line pressure is helpful with less clutch surface. 727 were beefy enough for use in diesels. They are overkill for a small cube v8 gas engine. The low gear set would allow a higher(lower numerically rear gear for economy while still having reasonable stoplight performance.
These trans with the lockup are plentiful.
Besides the clutch surface are the steel 4 pinion planetaries for heavy duty use. The distance from centre of the 999 low gear set is very similar to the 2:45 727 gearset with a better ratio. Most 904s use an aluminum front planetary which can fail in the splines. The best feature of the lockup 999 that will really increase your street or racing thrill is the 2.74 low gear that came standard in these trans. You will pay a hefty premium to get that ratio in a 727. The 904 comes standard with a riveted roller clutch, the 727 would require an aftermarket $$$ bolt in clutch.
In a performance application of any kind, the 727 user should be using an aftermarket steel or aluminum front drum, if you value your legs. The 904 does not have the problem of the drum exploding in a roller clutch failure. Looking at the 999 from that perspective, the 999 is strong enough and much cheaper to build, and will give better performance.
Yes you would have to do a few things to convert a lockup to non lockup if desired, but that really is just selecting the right parts from a donor trans. There are also performance lockup converters starting to appear on the market. This is why most feel that going from a 904 to a 727 is not really an upgrade.
Earlier I mentioned that the 904 is approximately .15 faster in the quarter mile, built equal to equal. Equal as in same first gear ratios. Changing from a 727 to a 999 with a 2:74 low gear, along with a cam change and a better matched converter dropped my et over half a second. Ymmv
 
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Aaaaah yes, TCI.
About 20 yrs ago I bought a TCI o'haul kit for my 727. Also came with TCIs shift kit.

The shift kit instructions were photo copies...very poor when you need clarity.
But worse was to come.....
As I read the instructions, they seemed familiar.......
I got out some old Transgo instructions & the TCI was a copy, just the odd word changed here & there to make it look like they were different.
Agree with other comments about usage. A Transgo shift kit, plus possible upgrades depending on usage.
 
Just my experience,
When my 727 in my 340 gts
Got tired I didn't have the money to rebuild it.
I had a simi fresh 998 from a 1987 dodge truck with a V6.
I put it in and it was like I had added 100hp!
Compared to the 727.
It has the low gear set, 4 pinion steel planetaries and 5 clutch drum.
Since then I went all through it, put 6 thin clutches in front drum, all Billet servos, and accumulator, Kevlar bands,
Rmvb, 3500 stall 9.5 "dynamic converter, deep aluminum pan, quicksilver shifter...etc
It works So Amazing I'm glad I made the switch.
My car is a daily driver with 400ish hp.
3.73 rear gears
It gets 17.5 mpg in town.
That's actually a bit better then it was with the 727.
Win Win
Mike

I just wanted to add,
I would not have known what to do as far as performance upgrades to my 904/998
Without the experienced members here and
Especially Robert at A & A transmission in Indiana.
He took the time to help me , answer all my questions and sell me exactly what I needed and nothing I didn't.
I bought all parts from A & A but the Converter. ( Sean at Dynamic was Awesome too! )
I highly recommend both of them.
Good luck on your project!!
 
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