20+ years of "Building 904/727 for drag racing use"

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rumblefish360 said:
In reading all of this information, I have a few questions!

Between the 904 & 727, there comes a point where parts, for ether, become limited. Between the two;

Which one would be the better choice for a 9 second ET car.
(In my case, it would currently be a small block Duster being built.)

Ultimately, which one can hold more power?

Where are their respective Tq. & HP limits?
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Rat Bastid said:
It gets to the point where you forget both the 904 and the 727 and get a TH400. The case becomes the weak link and AFAIK no one is making an aftermarket 727 case.
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I have an 8 second car that I run a 727 in with no issues, trans brake. My father and close friend have 3350+ lb B-body cars that run low 9s and both run the 727 with no issues, footbrake. I know DVW runs 8.90s on a 727 with a 3300+ lb B-body car. Another close friend of mine we are putting a 572 wedge in his Roadrunner next month that will hopefully weigh between 3300-3400lbs. 727 in that car as well, with a trans brake.

I am not saying the TH400 isn't a good alternative for a 3 speed because of the aftermarket case, but me personally I do not see the 727 case become an issue unless someone sends a stock front drum through it after a sprag failure. I am sure Duster346 can comment further on this regarding the torque and HP limits being that he has been doing 727s a lot longer than I have. However, when converting to a TH400, there will be a lot more money spent due to needing a different converter, shifter, etc.

rumblefish, I would say the 727 should suit your needs just fine. I am sure there are plenty on here that will say the 904 will work fine as well. I know I personally have seen many of 727s go down the track running in the 9s (Typically in B-bodies) with nothing more than a Cheetah old school RMVB, 4.2 or 5.0 lever, good front band, and 12 element bolt in sprag. In my opinion, for what you want to do, I would say a good front drum, good bolt in sprag (6 bolt 16 element), low band apply valve body, steel front planetery carrier, deep pan, billet low/reverse servo, rear roller support, hardened pump gears, 4.2 lever, should last plenty long in a small block A body that runs 9s. You can do more upgrades but I think you would be fine with the ones I listed. I hope Duster346 and other experienced builders would agree.
 
Thanks. Duster346 did PM me. On this project, I’m still a bit far out. It’s third in line at the moment. But a goal I want to try for.
 
rumblefish360 said:
In reading all of this information, I have a few questions!

Between the 904 & 727, there comes a point where parts, for ether, become limited. Between the two;

Which one would be the better choice for a 9 second ET car.
(In my case, it would currently be a small block Duster being built.)

Ultimately, which one can hold more power?

Where are their respective Tq. & HP limits?
Click to expand...
There are a lot of things that need to be known about the combination, but I'd typically recommend a 904 for a small block powered car that is lighter with smaller tires. A 727 will of course work fine, but it will be slower than a 904. My footbrake 727 in that car at that ET would go 1500+ runs before needing a freshen up. Freshen up intervals on the 904 would be shorter. The 904 would cost slightly more to build than a 727 for a 9 second car.

Obviously, the 727 can hold more power than a 904.

For conservative numbers we will build a 904 for 1000hp, and a 727 for 1500hp. The blue supercharged Challenger that used my 727 made more than 1500hp.
 
Duster346 said:
What kind of case breakage have you seen?

The majority of case and extension housing breakage is going to all be related to how the chassis is setup.
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I‘ve seen them explode. Aftermarket cases aren’t made because someone wanted to open a new market.

Lets not turn this into the thread equivalent of aftermarket blocks.

If you want to run a TF with big power and a stock case, by all means have at it.

I run clutches so what the converter crowd does has little bearing on what I care about.

Defending a transmission because of brand is the same as saying you can stay with the 8.75 axle even though the 9 inch is far stronger.
 
Rat Bastid said:
I‘ve seen them explode.
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Transmission cases don't explode. The parts inside of them can, however.

And for the record, a local racer exploded a stock high gear drum in a T400 through the lights at our local track recently. Exploding drums isn't just a torqueflite problem.

If you are implying that you need an sfi case to contain an explosion, that is certainly a valid argument, but if the transmission is built properly and has billet drums the chance of having an explosion is practically 0%.
 
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Rat Bastid said:
I‘ve seen them explode. Aftermarket cases aren’t made because someone wanted to open a new market.

Lets not turn this into the thread equivalent of aftermarket blocks.

If you want to run a TF with big power and a stock case, by all means have at it.

I run clutches so what the converter crowd does has little bearing on what I care about.

Defending a transmission because of brand is the same as saying you can stay with the 8.75 axle even though the 9 inch is far stronger.
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I wouldn’t say anyone is defending a transmission purely because of brand. But the 727 will handle a lot of power and as Duster346 has just gave conservative numbers of 1500hp for the 727 and 1000hp for the 904 cases. I’d consider 1000-1500hp a lot of power. So to say the 727 won’t handle power is false.

My example, my personally owned 727 came which out of a top sportsman car that ran 4.70s on nitrous, 2700lbs 1970 GTX tube chassis. The 727 was built by Rick Allison in 2006. I bought the 727 used off of a friend who bought the GTX and decided to change its setup. I put the 727 in my car which runs 5.50s-5.60s. Never tore it down before putting it in. Ran the trans 500 runs before I had converter fins start to fail and put metal through the trans. I tore it apart, for precautionary measures, and found nothing was harmed inside. The clutches and steels looked great, could still read the writing on them and I have no clue how long they were in there before I took it apart. I freshened the trans and back in the car it goes. Worked just as good as when I took it out. Not that I am laying down an overwhelming amount of power, but for running what my car runs, my 727 works well for me.


Trust me, I see your point about the TH400 having an advantage of the aftermarket case but for a Mopar naturally aspirated racer (which I believe most of us are) who wants to simply run 9s with an A body small block, the 727 or 904 will work just fine.
 
71Demon528 said:
I wouldn’t say anyone is defending a transmission purely because of brand. But the 727 will handle a lot of power and as Duster346 has just gave conservative numbers of 1500hp for the 727 and 1000hp for the 904 cases. I’d consider 1000-1500hp a lot of power. So to say the 727 won’t handle power is false.

My example, my personally owned 727 came which out of a top sportsman car that ran 4.70s on nitrous, 2700lbs 1970 GTX tube chassis. The 727 was built by Rick Allison in 2006. I bought the 727 used off of a friend who bought the GTX and decided to change its setup. I put the 727 in my car which runs 5.50s-5.60s. Never tore it down before putting it in. Ran the trans 500 runs before I had converter fins start to fail and put metal through the trans. I tore it apart, for precautionary measures, and found nothing was harmed inside. The clutches and steels looked great, could still read the writing on them and I have no clue how long they were in there before I took it apart. I freshened the trans and back in the car it goes. Worked just as good as when I took it out. Not that I am laying down an overwhelming amount of power, but for running what my car runs, my 727 works well for me.


Trust me, I see your point about the TH400 having an advantage of the aftermarket case but for a Mopar naturally aspirated racer (which I believe most of us are) who wants to simply run 9s with an A body small block, the 727 or 904 will work just fine.
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That’s what I’m saying. How much risk is worth it? Transmissions fail. Especially when pushed.

If someone made an SFI approved TF case I’d pick the TF over the TH all day long.

There is a saying in the street bike world. There are those who have gone down, and those who are going to go down. It’s the nature of it.

That’s why when I rode I had the best equipment I could afford. I’m risk averse.

I‘m the same with racing parts. I’ve broken enough of the best the aftermarket has to offer that I don’t usually try and push stock stuff if I can avoid it.
 
Duster346 said:
Transmission cases don't explode. The parts inside of them can, however.

And for the record, a local racer exploded a stock high gear drum in a T400 through the lights at our local track recently. Exploding drums isn't just a torqueflite problem.

If you are implying that you need an sfi case to contain an explosion, that is certainly a valid argument, but if the transmission is built properly and has billet drums the chance of having an explosion is practically 0%.
Click to expand...


Right. It’s a HUGE safety factor.

I always factor in driver error/abuse in my thinking because it happens. A lot.
 
Duster346 said:
Transmission cases don't explode. The parts inside of them can, however.

And for the record, a local racer exploded a stock high gear drum in a T400 through the lights at our local track recently. Exploding drums isn't just a torqueflite problem.

If you are implying that you need an sfi case to contain an explosion, that is certainly a valid argument, but if the transmission is built properly and has billet drums the chance of having an explosion is practically 0%.
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Agreed, John Cope explains the 727 drum explosion very well on a YouTube video, but he also rightfully mentioned the 727 drum fail on the line and turbo 400 fail in the top end of the run.
 
j par said:
View attachment 1716047478

View attachment 1716047479
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The Transgo kit that I am installing in my 727 advises to turn or grind the (looking at your picture) right shoulder down approx 1/2 way. This apperantly alleviates the problem of the servo cocking in the bore. I noticed evidence on the side of the servo bore of some scuffing. Lucky for me, I couldn't feel the scuff so very minor. This according to my Trans-go TF1 instructions.
 
CFD244 said:
The Transgo kit that I am installing in my 727 advises to turn or grind the (looking at your picture) right shoulder down approx 1/2 way. This apperantly alleviates the problem of the servo cocking in the bore. I noticed evidence on the side of the servo bore of some scuffing. Lucky for me, I couldn't feel the scuff so very minor. This according to my Trans-go TF1 instructions.
Click to expand...
I don't recall that, but I've only done TF 2's and 3's.. I have the instructions still, I'll have to check it out.,
 
Duster346 said:
There are a lot of things that need to be known about the combination, but I'd typically recommend a 904 for a small block powered car that is lighter with smaller tires. A 727 will of course work fine, but it will be slower than a 904. My footbrake 727 in that car at that ET would go 1500+ runs before needing a freshen up. Freshen up intervals on the 904 would be shorter. The 904 would cost slightly more to build than a 727 for a 9 second car.

Obviously, the 727 can hold more power than a 904.

For conservative numbers we will build a 904 for 1000hp, and a 727 for 1500hp. The blue supercharged Challenger that used my 727 made more than 1500hp.
Click to expand...
Chris, what would you consider the base modifications for a 904 going from stock to using a trans brake? Engine HP ~400, 3000#-3200# car.
 
Duster346 said:
Transmission cases don't explode. The parts inside of them can, however.

And for the record, a local racer exploded a stock high gear drum in a T400 through the lights at our local track recently. Exploding drums isn't just a torqueflite problem.

If you are implying that you need an sfi case to contain an explosion, that is certainly a valid argument, but if the transmission is built properly and has billet drums the chance of having an explosion is practically 0%.
Click to expand...

I just read on another forum that a SS guy (I think he’s a Ford guy) says he’s using a Proflite in his car.

Evidently he’s not using an SFI case because AFAIK a you can’t get one.

Like I said before, if you could get an aftermarket case for the TF everyone would switch to it.

The smart guys in the classes where it matter are using the TF.
 
I talked with Rick Allison this summer at the Mopar Nats and he gave me hope about developing one. Fingers crossed.
 
That would be really nice to have as an option in the arsenal.
 
dart_68 said:
Chris, what would you consider the base modifications for a 904 going from stock to using a trans brake? Engine HP ~400, 3000#-3200# car.
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At that lower power it'd be a pretty mild build but would look like this:
- red racing clutches and bands (Rigid 2nd gear band)
- billet servos
- HD band strut
- 4.2 2nd apply lever
- Teflon sealing rings for stator/pump support
- multi-spring kit for 3rd gear drum
- oem steel 4 pinion planetary front and rear
- re-vent to the back of the case and a few other mods needed for transbrake
 
Duster346 said:
At that lower power it'd be a pretty mild build but would look like this:
- red racing clutches and bands (Rigid 2nd gear band)
- billet servos
- HD band strut
- 4.2 2nd apply lever
- Teflon sealing rings for stator/pump support
- multi-spring kit for 3rd gear drum
- oem steel 4 pinion planetary front and rear
- re-vent to the back of the case and a few other mods needed for transbrake
Click to expand...
Thanks for the info Chris! It's very helpful in how I want to proceed looking forward.
 
Duane said:
Yes I would agree that it’s better, but he is saying it’s application specific and I don’t understand why the application would matter.
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I “believe“ the application would be like a high HP big tire car and the consequences of tire shake. i understand the larger 727 style sprag holds up a little better in that situation.
 
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