1977 904 horsepower limits?

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Caco2120

Caco2120

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Hello guys.

In bone stock, 60k mile trim....what would be the boom point on a stock 1977 904?

I know it may be a silly question, but most transmissions seem to have a "wives tale" type hp limit.

Any input on flywheel hp?
350? 400? 450?

Would a manual valve body prolong life at all by eliminating the slips between shifts?

Thanks all for the opinions.
 
Caco2120 said:
Hello guys.

In bone stock, 60k mile trim....what would be the boom point on a stock 1977 904?

I know it may be a silly question, but most transmissions seem to have a "wives tale" type hp limit.

Any input on flywheel hp?
350? 400? 450?

Would a manual valve body prolong life at all by eliminating the slips between shifts?

Thanks all for the opinions.
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well im not sure about going boom but a mild 360 with only a performer cam and 4 barrel roasted the clutch packs in a stock 904 in my 73 duster I had a while back. it didn't go "boom" just burnt it up from heat caused by slippage.
 
Usually 2nd gear will be the first to go, at least my experiences.
 
Just built a 904. They will hold up past 450 hp.

20171210_151641.jpg
 
It depends on how well the 904 is built. A properly built 904 can handle up to 500 hp. Use high quality performance clutches and bands and you'll be all set! 65'
 
Plymouth 65 said:
It depends on how well the 904 is built. A properly built 904 can handle up to 500 hp. Use high quality performance clutches and bands and you'll be all set! 65'
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yes, built they do well. Perhaps list brand/part number for the clutches/bands you are talking about incase the op should decide to freshen up the 41 yr old tranny?
 
Well that's an extremely loaded question. What would a freshly rebuilt 1977 tranny hold? What would a 1977 tranny that has 60,000 miles that's at all its life? That was used periodically? That had the fluids changed regularly? That had the bands adjusted all its life properly? And the big one the pressure sensor was it adjusted correctly all its life and is it now?
The 904 seems to be the drag racers choice, so I wouldn't see one of these having any problem holding horsepower.
 
Not a loaded question. I’ve ran them behind my mud rail trucks making in the 500 600 hp range bone stock. Yes the better parts put together by a good tranny makes them last a bit longer but that 904 makes more power to the ground than a light weight 727 is why we preferred them over the 727 in the slower classes
 
Plumcrazyreindeer said:
Not a loaded question. I’ve ran them behind my mud rail trucks making in the 500 600 hp range bone stock. Yes the better parts put together by a good tranny makes them last a bit longer but that 904 makes more power to the ground than a light weight 727 is why we preferred them over the 727 in the slower classes
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While I agree with you there's no rocket science to how much horsepower a 904 will likely hold with a fresh rebuild for a purpose-built car. BUT, predicting how much a 60,000 mile, 41 year old transmission, with unknown history not being a loaded question?
With that said in 1977 904 I would believe to be a better candidate for a purpose-built rebuild then maybe an older one? It's been my experience the very little I have rebuilding 904 that the later years where for lack of better terms beefier?
 
Thanks guys. I meant the above in stock form.

I didnt literally mean explode...but failire of the clutches.

I realize its not brand new. And rebuilding it would help longevity. This is a currently operating trans behind a 318.

I had heard many say a gm 700r4 is only good for 400 horse stock, and helped a friend install a stroker 383 on a truck. The trans ran fine before. Lasted about 5 hard pulls and the clutches let go.

Wondered if there was a similar wives tale for a stock 904.
 
In my world it will last as long as it will last in a 1900lb rail. in a car on the concrete in town on the highway I would be conservative with the abuse you give a 904 unless it’s purpose built like Plymouth 65 said no matter the age. Cousin has one behind a 340 in a half ton swb85 it has 85k original on it with a 318. When we put the 340 in his truck it lasted not long befor he had to get it built right. He spent about 1500 plus a converter to match the motor and it’s been his daily driver for about 10k. The new 340 makes about 400 on motor never sprayed in front of the stock 904
 
318willrun said:
yes, built they do well. Perhaps list brand/part number for the clutches/bands you are talking about incase the op should decide to freshen up the 41 yr old tranny?
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Not sure on part numbers etc... we used a local transmission shop to build the 904 a little stouter. A decent transmission guy knows 727s and 904s. I’m no transmission guy I just tell them what I need and they try to get me there. Lol
 
Plumcrazyreindeer said:
Not sure on part numbers etc... we used a local transmission shop to build the 904 a little stouter. A decent transmission guy knows 727s and 904s. I’m no transmission guy I just tell them what I need and they try to get me there. Lol
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About how much it cost you for the rebuild?
 
slipyoke said:
About how much it cost you for the rebuild?
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$1500ish. If you need a different converter it’s about $300 to have the one you have to act the way you want. It’s about $950 for a new 8 inch converter on the cheaper end the price just goes up from ther on converters. If you making much more power than 400hp I would get the flexplate and converter for the bigger bolts like a SFI aproved setup that uses Bbm or Chevy bolts. SFI flexplate is around $100
 
slipyoke said:
About how much it cost you for the rebuild?
Click to expand...

So in other words to give you the best bang for the buck $2500 to make it a better setup. About $1800 to build up the trans and use your stock converter and have the stall increased. $1500 to just make the trans a little stouter. This is just from my experience estimated prices from having a local trans guy doing the work. Some of these online trans businesses like monster or any other big name guys can build to order and are good quality but they can be a bit more pricey from my experience. The guy I use is is just a local yocal but if I want something built new I use trans king in Conroe TX
 
Plumcrazyreindeer said:
So in other words to give you the best bang for the buck $2500 to make it a better setup. About $1800 to build up the trans and use your stock converter and have the stall increased. $1500 to just make the trans a little stouter. This is just from my experience estimated prices from having a local trans guy doing the work. Some of these online trans businesses like monster or any other big name guys can build to order and are good quality but they can be a bit more pricey from my experience. The guy I use is is just a local yocal but if I want something built new I use trans king in Conroe TX
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maybe depends on where you are. Here, just a "bench job rebuild" is about 400 - 450 without converter. I just paid 650 out the door for a rebuild on a 727 with new converter out of a 4x4. I paid 750 for 904 with some upgrades to strengthen it like kelvalar bands and some things to make it stronger - without converter.
 
Like any transmission, put enough money into it, and a 904 will take a ton of hp and torque. My ex-bosses car ran a 1200HP + Steve Schmidt pro-stock engine in his BA/A Pontiac and it had a 904 in it. It was a test mule for the performance automatic parts they make. He set a BA/A record with that car running the 904.
A lot of the SS/AA Cudas and Darts either had a highly modified 904 in it, or a 727 with 904 innards.
 
transman said:
Like any transmission, put enough money into it, and a 904 will take a ton of hp and torque. My ex-bosses car ran a 1200HP + Steve Schmidt pro-stock engine in his BA/A Pontiac and it had a 904 in it. It was a test mule for the performance automatic parts they make. He set a BA/A record with that car running the 904.
A lot of the SS/AA Cudas and Darts either had a highly modified 904 in it, or a 727 with 904 innards.
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What i wished is that somebody would make a list of the few upgrades needed to run a 904 comfortably behind, per say, a 375-400 hp 360. Kind of like "if you do x, y, z, you'll be fine for years...."

I can testify that if you run even high 13's with a original stock 904, you'll smoke bands and clutches. I've always lost 2nd gear, the first thing to go. I also know you can pull a good shifting stock 727 and it will hold up well. So, what is the basic parts list for upgrades to a 904? this question is asked a lot here... the 904 question i mean
 
Use to be several list of parts list on here but got lost in software upgrade
 
70aarcuda said:
Use to be several list of parts list on here but got lost in software upgrade
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you build your own, correct? What would you recommend for minimal "minor" upgrades to make a 904 stand behind a 375 hp 360 in a street car. Kevlar bands? junior shift kit? spring or clutch upgrades?
 
Go to www.tcsproducts.com and look through their web page and see what is available for the 904. They and other performance automatic transmission companies will have what you need to build any 904 you want.
If it was mine: and I wasn't racing --> Raybestos waffle lined friction plates, along with new steel plates, Overhaul gasket and seal kit of course, new bands (Kevlar if you so desire), bushing kit, washer kit, roller sprag kit, TF-2 transgo shift kit, filter, output shaft bearing (it's old and got a lot of miles on it). In other words, a complete, no short cuts taken rebuild. Check and then recheck the planataries for excessive wear or sloppiness, look closely at the pump gears and replace if questionable, look at the input shaft for spline wear, replace the forward clutch diaphragm spring (prone to cracking) and look closely at the two drums for wear. Update the reverse servo piston, get the intermediate accumulator repair kit. I would think that this would/could hold up to 350/400 HP.
Now if you're racing, that opens up a whole other thing. Getting ANY transmission to live up to the racing life depends on the thickness of your wallet.
Others may disagree.
 
have been using stock disc and steels...Kevlar bands...billet rear servo in a few of them MOPAR 904 500 42RH 42RE TRANSMISSION BILLET REAR SERVO KIT, DODGE, PLYMOUTH AMC | eBay some I use this servo..actually been upgrading to the MrRandy servo went I rebuild them...think I got 2 or 3 with that servo and I use this servo for the most part...42RE 42RH A904 Transmission Sonnax Rear Servo Piston 22912A | eBay

all the 904 with transbrakes (Tranzact of Indy) use the 24 spring kit in the front clutch...all the front clutches have 5 disc in them....and If the pump gear looks iffy...I change it out...I have used both Teflon and steel rings...No accumulator is required with manual valve bodies...I have one trans with a ATi wound front clutch spring but it has even to hit the track since the car is still waiting for me to work on it.

I don't buy kits...I order parts in bulk....like 10 disc..10 steels...then half dozen lip seals...and pump seals...so I always have enough parts on hand should I need to repair a transmission..
 
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My guy does my transmissions for 600-800 dollars.

Uses bolt in sprag, alto red clutches. Machines drum for an extra clutch. Forget what band. Know it isn’t a Kevlar one. He doesn’t like them for my street use. . 3.8-4.2 kickdown leaver and his Home made shift kit.

I don’t bother with getting stock converters tweaked. I call dynamic and have one built for me. More expensive hell yea but the difference is incredible. And don’t even bother with the stock flexplate. Go get a sfi one with the larger bolts. Do it right do it once.
 
a stock 904 sprag is bolted in....just drill out the head rivets and it come out...completely different then a 727...
 
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