Rebuild 904 or swap for 727?

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CudaFactHackJob said:
It's not my job to care about my customers' well-being. IF they want to play it safe, then buy a volvo with the extra side air bags. I'm here to help make their car a very dangerous piece of transportation from one stop light to the next. If they die, they die; as long as their transmission doesn't die. You're showing pics of 727s that were destroyed by god knows what; but pretty sure it was a lot more power than what 99% of small blocks put out. Too bad chrysler never put the 904 behind bbs so we could have a realistic historical comparison. Why spend money on a hardened 904 input shaft? and don't forget that when you want the right return springs on your 904 direct drum; that you can find somebody who knows wth you are even talking about. Most guys that come to me are just glad they found somebody who knows ANYTHING about performance TFs, and isn't trying to "upgrade" their own wallet. You know tons about these trannys, but most of it doesn't apply to 95% of the dudes on here who just want a weekend warrior.
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Ok finally you have made a realistic post. Yes a guy that is just looking for a reliable economical build would be looking for a guy like you that just charges a fair price. I get that. Kudos to you.
I spent the money on a hardened input shaft because of my anticipated performance level.
That may be the first area of weakness. Ati transmission built the 904 for the first Chrysler drag pak. At that cars performance level the input shafts were failing.
I cannot confirm this story, but rumour is that when Chrysler was building the hemi super stockers back in the 60,s, they built a small number of them in Canada with the 904. NHRA would not recognize those cars.
Hence the birth of Protrans who began putting the 904 guts in a 727
To get around the rules.
The pic in my last post( not the Chev) are what happens to the stock drum at high rpm in first gear if the sprag is unknowingly failed.
The planetary gearset is designed to spin the front drum at an rpm
That is within its safe operating rpm. But this safe rpm relys on the sprag to hold. If the sprag does not hold, a new ratio is created
That spins the drum way past its intended safe rpm and centrifugal force
Combined with the material of the stock drum, becomes a grenade as the drum flys apart. That is why I said that it's not a horsepower issue. There is a member on here cracked back I believe that said that he had a station wagon towing a trailer and the drum exploded.
It would be very very rare for it to happen in just a daily driver.
But in a performance car, where you know the guy is gonna do bunny hops on the street and the like at any significant rpm,
The stock drum can be very dangerous. That's why locomotion recommended that a performance street car should use a valve body with low band apply. This problem with the 727 is so prevalent that John Cope racing will not make any of his performance valve bodies without low band apply. Low band apply uses the rear band to assist the sprag in holding under high torque so the sprag cannot fail. But there were many performance valve bodies made without low band apply. On the street if the guy is gonna goof off, he should have low band apply.
I have seen 14 seconds cars go up in flames when all the trans fluid got on the headers. Guys have lost feet, cars ruined, windshields
Broken. You have to have seen one let go to believe it.
They look jus like in that picture.
 
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I don't like the low band apply cuz it complicates the 1-2 shift. Instead of just applying the intermediate band for second, it has to release the low band at the same time; who needs that overlap; (might lose .25 seconds..). That's why I design mine to be raced in "D". Take off in first gear with the lever in "D" and the low band isn't applied.PS You have to remember Duane, my posts aren't written for you, but to help the guy who's working on his own car and needs some input as to how to build a car on a budget. So I'll argue with you and let them make their own choice, based on the info that comes out of our discussions. Everybody already knows that the only thing that beats cubic inches; is cubic dollars, but when it comes to Chrysler's best trans, just stick with the 727 whenever possible and move on to things on your car that really do need upgrading.
 
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CudaFactHackJob said:
I don't like the low band apply cuz it complicates the 1-2 shift. Instead of just applying the intermediate band for second, it has to release the low band at the same time; who needs that overlap; (might lose .25 seconds..). That's why I design mine to be raced in "D". Take off in first gear with the lever in "D" and the low band isn't applied.PS You have to remember Duane, my posts aren't written for you, but to help the guy who's working on his own car and needs some input as to how to build a car on a budget. So I'll argue with you and let them make their own choice, based on the info that comes out of our discussions. Everybody already knows that the only thing that beats cubic inches; is cubic dollars, but when it comes to Chrysler's best trans, just stick with the 727 whenever possible and move on to things on your car that really do need upgrading.
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I like this post and I will tell you why. You brought up an area of the Torqueflite that I don't have experience and that is the low band apply and how it complicates the 1-2 shift.
I bought a tranzact brake with low band apply.
All Torqueflite brakes apply the band when the brake is on.
All of them. It's what happens to the band after you let go of the button. Here is where there are differences among different companies. It is hard to get the secrets from the differing manufacturers.
Turbo action years ago touted his timed release of the band.
In other words they don't shut the band off right away because the theory goes that if your slicks were to hook and then spin, while still in first gear. This spin in first gear can still damage the sprag, but as you have said, you don't want to mess up the 1-2 shift.
In the last say ten years or so we started to see the manufactures release brakes with a billet aluminum bottom valve body.
I could not understand the reason for this.
Then later we started to see billet aluminum brakes with the band on right until you pull the shifter to second gear. No timed release.
The manufacturers claimed a clean shift. How can this be.
I have one of these now.
In one of John Cope YouTube videos, he explains that when you buy one of his low band apply valve bodies, brake or manual shift,
You must also buy his rear servo kits for it to work right.
According to John these aluminum billet valve bodies have custom
Machined oil passages that allow the fluid to move faster and the servo is solid with a much higher return spring pressure to shut the band off really quick. On top of this, he recommends a band adjust
On a 904 with double wrap band of only 2.5 turns out from 72 inch pounds. It seems too tight to me and the factory manual calls for 4 turns.
I asked John about this band setting, and all he would say is 4 turns is too loose, but he won't explain why.
I am speculating that for a drag car only, this tighter setting also speeds up the shut off of the band to get a clean 1-2 shift but I don't know for sure.
What do you think ?
 
CudaFactHackJob said:
I don't like the low band apply cuz it complicates the 1-2 shift. Instead of just applying the intermediate band for second, it has to release the low band at the same time; who needs that overlap; (might lose .25 seconds..). That's why I design mine to be raced in "D". Take off in first gear with the lever in "D" and the low band isn't applied.PS You have to remember Duane, my posts aren't written for you, but to help the guy who's working on his own car and needs some input as to how to build a car on a budget. So I'll argue with you and let them make their own choice, based on the info that comes out of our discussions. Everybody already knows that the only thing that beats cubic inches; is cubic dollars, but when it comes to Chrysler's best trans, just stick with the 727 whenever possible and move on to things on your car that really do need upgrading.
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You will notice that most guys that ask which trans to use will say to use what you already have, like you said to save money.
If he has a 727 use it.
If you have a 904 although it's weaker, it will still get the job done for a typical street strip car. I 100% agree that it is not as strong as a727, no argument, but its overkill for say an a body with a mild small block. Use what you got, it's cheaper, don't need a driveshaft.
But I get your points, I just hope that you get mine and the other posters as well.
 
You would think that in a place like Southern California; where I live, that there would be TF experts coming out of the woodwork; but there isn't. Every trans that comes in here has been apart several times, and the slop and junk I run across is astounding. They just slap a kit in it and call it good. I have people drive up from San Diego and over from Los Angeles; even a few from Arizona. But it's partially understandable; considering you can't even find a kit that replaces the direct pack with an extra steel and thin Red Eagles for the direct clutch; the easiest upgrade ever.
 
CudaFactHackJob said:
You would think that in a place like Southern California; where I live, that there would be TF experts coming out of the woodwork; but there isn't. Every trans that comes in here has been apart several times, and the slop and junk I run across is astounding. They just slap a kit in it and call it good. I have people drive up from San Diego and over from Los Angeles; even a few from Arizona. But it's partially understandable; considering you can't even find a kit that replaces the direct pack with an extra steel and thin Red Eagles for the direct clutch; the easiest upgrade ever.
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CudaFactHackJob said:
You would think that in a place like Southern California; where I live, that there would be TF experts coming out of the woodwork; but there isn't. Every trans that comes in here has been apart several times, and the slop and junk I run across is astounding. They just slap a kit in it and call it good. I have people drive up from San Diego and over from Los Angeles; even a few from Arizona. But it's partially understandable; considering you can't even find a kit that replaces the direct pack with an extra steel and thin Red Eagles for the direct clutch; the easiest upgrade ever.
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You should go into the Torqueflite race trans business. Maybe there is a market for that in your area, lol
 
They just waste my time with all their dumb ideas they read about online. I mostly do street trannys. I ask them their hp level and rpm shift point and give them a price. When they start telling me what they want in it....I say, "I think you're looking for the AAMCO experience."
 
CudaFactHackJob said:
They just waste my time with all their dumb ideas they read about online. I mostly do street trannys. I ask them their hp level and rpm shift point and give them a price. When they start telling me what they want in it....I say, "I think you're looking for the AAMCO experience."
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I found this online. Notice the engine rpm that would fail a stock drum if the sprag were failed. Very easy to blow up.
Tcs makes a lot of the aftermarket drums and performance trans parts on the market.

image.png
 
LOL. Wow, I didn't realize I would stir up such a hornets nest. I asked the original question and read all the replies. Some of the information was above my head and some just hurt my head. This car will be a street rod and probably not get onto the track more than a couple of times and for more fun than trophy chasing.
In short, I gathered the following:
My existing 904 will fit and be strong enough to handle the 360 I will put in front of it. (so just rebuild it for piece of mind)
If I wanted to swap out to a 727, I would have to get one and possibly modify the firewall and floor??
 
Bob Wilkie said:
LOL. Wow, I didn't realize I would stir up such a hornets nest. I asked the original question and read all the replies. Some of the information was above my head and some just hurt my head. This car will be a street rod and probably not get onto the track more than a couple of times and for more fun than trophy chasing.
In short, I gathered the following:
My existing 904 will fit and be strong enough to handle the 360 I will put in front of it. (so just rebuild it for piece of mind)
If I wanted to swap out to a 727, I would have to get one and possibly modify the firewall and floor??
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67-up no modifications needed. Bolt in deal. Driveshaft needs to be shortened though. And 727 yoke.

My opinion is still to do a quality rebuild with quality parts and use the 904.
 
Everybody talks about "quality parts" as if there are junk parts available. I would like to be made aware of any "un-quality" parts available..In forty plus years, I have NEVER found any sub par transmission parts. The strange thing to me is that; knowing the weakness of the direct clutch pack, I hardly ever hear anyone refer to using .061 performance fibers; allowing for an extra plate. If you aren't aware of this trick, then you don't know the first thing about a "quality rebuild using quality parts".
 
Based on the totality of this thread, I will have someone rebuild the existing 904.
What upgrades or reliable tricks do you recommend and why?
What specific parts or kits do you recommend and why?
Thanks again to you all for the assist!
 
Bob Wilkie said:
If I rebuild the 904, what would you recommend I tell the shop who rebuilds it to use or do?
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Pretty much a guarantee that they will tell you what they will use. You start telling them you want this or that they’re likely to recommend you do it yourself or you better be prepared to explain to them why you think you need x, y and/or z when they may say you don’t, that they do things their way. Just a touch of reality here, I’d theorize most shops are going to use what they like to use.
Bob Wilkie said:
Should I replace the smaller 7260 u-joints and re-use the driveshaft or replace it with a larger one and 7290 u-joints?
If replace, what do you recommend?
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Have you looked at what it would cost to change the slip yoke, differential yoke, have a new driveshaft fabricated with new yokes etc?? Just wondering: why are you thinking that you might need to swap out the 7260 yokes/u-joints?
Its your money, but the 7260 setup will be all you will ever need. I’d spend that cash on the converter.
 
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12many said:
Pretty much a guarantee that they will tell you what they will use. You start telling them you want this or that they’re likely to recommend you do it yourself or you better be prepared to explain to them why you think you need x, y and/or z when they may say you don’t, that they do things their way. Just a touch of reality here, I’d theorize most shops are going to use what they like to use.

Have you looked at what it would cost to change the slip yoke, differential yoke, have a new driveshaft fabricated with new yokes etc?? Just wondering: why are you thinking that you might need to swap out the 7260 yokes/u-joints?
Its your money, but the 7260 setup will be all you will ever need. I’d spend that cash on the converter.
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I first asked that question because I was always under the impression that the 7260 joints were smaller and thereby weaker. I have since heard from several people that they will be fine for my setup. I will just have the 904 rebuilt and keep the same driveshaft and yokes with new 7260 joints.
 
12many said:
Pretty much a guarantee that they will tell you what they will use. You start telling them you want this or that they’re likely to recommend you do it yourself or you better be prepared to explain to them why you think you need x, y and/or z when they may say you don’t, that they do things their way. Just a touch of reality here, I’d theorize most shops are going to use what they like to use.
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I will see what shops have a good reputation around me and have them rebuild the 904 using whatever parts or kits they suggest.
 
Bob Wilkie said:
I will see what shops have a good reputation around me and have them rebuild the 904 using whatever parts or kits they suggest.
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I think any shop that recommends using Alto red frictions w/Kolene steels, red lined bands, and installing a Transgo TF2 shift kit would cover the basics, be a standard? There are a lot of other things that can be done, upgraded components that would be optional, beyond a standard performance rebuild. As to a converter I would consult companies like Turbo Action, FTI, PTC (generally $600-700 range) or perhaps any well regarded regional companies with your specs vs. relying on a shops recommendations. :)
 
Bob Wilkie said:
Based on the totality of this thread, I will have someone rebuild the existing 904.
What upgrades or reliable tricks do you recommend and why?
What specific parts or kits do you recommend and why?
Thanks again to you all for the assist!
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Even for your application I will vouch for what Cudafact said in his previous post. Use the thinner clutches to add more clutches,
Particularly in the front drum as this is a shifting clutch that wears.
More clutches there will add durability. Also on this same clutch drum, I would add the multi spring pack. It will give better shift timing or improved overlap. A wider 2nd gear band will add durability as well. I have used these thinner clutches in my diesel truck and have 25,000 miles on them with no ill effects.
 
I've heard of using five oem thin forward frictions in the direct clutch, but I only use hi-performance thins in there (.061). The original direct frictions were thicker steel and thicker friction material (plus grooved) because the third gear clutch engages at a higher rpm than the forward clutch. But Alto Red Eagle friction material has a much higher burning temperature than oem. I think Red Eagle makes the grooved plates for those nervous about wandering too far from stock, but they lose 20% of the contact area. The th400 and the C6 And C4 use smooth plates in direct a lot of the time. Anybody have a problem with smooth plates in the TF direct pack? Weird shifting or hanging up?
 
I put 6 thin Grooved red altos in my direct drum.
I was going to use smooth frictions but
A & A transmission recommend the grooved ones.
Maybe because it's a Driver only?
BTW. I changed my transmission from a 727 to a 904 and it's one of the best improvements I've done so far!
I think mainly because it has the low gear set and adds bottom end acceleration for a city driver.
Op good luck with your car!
Good choice staying 904. Imo
 
Most 904s have a higher stall converter. What method did you use to install SIX frictions into the direct drum? Thinner top plate? Figuring the grooves take up 20% of the surface area, then four smooths equal five grooved.
 
CudaFactHackJob said:
Most 904s have a higher stall converter. What method did you use to install SIX frictions into the direct drum? Thinner top plate? Figuring the grooves take up 20% of the surface area, then four smooths equal five grooved.
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Yes I used a thinner top plate and snap ring
The drum was already a 5 disc one
Plus I used different thickness steels
To get the clearance I wanted.
Went with a 3500 9.5" dynamic converter
 
Personal experience:
A built 904 will serve you well. I would stick with the 904 (A999's are even better if you can find them).
I lucked out and found an A999 out of a old police cruiser (88' Diplomat) in the junkyard.
Put in kolene steels, red eagle clutches and kevlar bands.
I also converted it to non-lockup (which I regret, see below). And put a Cheetah stage 2 valve body from Turbo-Action.
Total cost for was about $1200, HOWEVER that is because I did most of the work myself with an 30+ yr trans tech helping me out.
I have almost 50,000 daily driven miles on this trans behind a fairly beefed up 360.
We're both even confident that it'll survive easily behind the 408 stroker I'm building.
My only advice is: If it's a street car stick with the lock-up and just shell out the clams for a good LU torque converter and level 2 valve body kit. I kinda wished I did, the 200-250 lower rpm on the freeway would've been great.
 
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CudaFactHackJob said:
Most 904s have a higher stall converter. What method did you use to install SIX frictions into the direct drum? Thinner top plate? Figuring the grooves take up 20% of the surface area, then four smooths equal five grooved.
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With as much disinformation as there is regarding transmissions, maybe you should think about doing a "what parts to use" thread regarding the 727 and 904. I know I for one would appreciate it.
 
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I wish that was possible, but every situation is different because it depends on what you have and what you intend to do with it. The 71 to 78 727s are the best, but many times parts have been switched with older units so that can't even be a rule of thumb. And with 904s, there are later 998 and 999 units that have some fantastic upgrades; like more clutches, wider band, lower gears, and dual bushings in the direct drum, but it can be confusing and sometimes machining is necessary to adapt the upgrades into an older 904. Plus the fact that the "upgraded" 904s; the 998 and 999s; are all lockups from what I've seen, and those converters are more expensive. So what we end up with is a situation where folks think all these fantastic upgrades are a bolt-in for the old 904, but most of them aren't. A trans with six thin direct Red Eagles, wider kevlar band, and low first gearset is a killer tranny, but don't confuse that with a 904 with four directs; the strength difference is night and day. That's why I steer customers to wards the 727; it's cheaper. And another thing...just because some place rebuilds trannies, don't even go thinking they can build a performance anything. There are 904 specialists and there aren't. I have never met one. The one individual I have confidence in as a 904 specialist (besides myself) is Duane, but his knowledge far surpasses mine in upgrading the 904 to the better pieces with machine work.
 
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