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

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Duster346 said:
There can be. I'd say up to 500hp naturally aspirated with a lighter car you'd be fine. I've built several.

However, the weak link will be the factory input shaft/forward drum. The input shaft can rip out of the drum.

There is not an upgraded input shaft/hub assembly for the A500, 42/44RH&RE transmissions available at this time.

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What about for a 904? I take it there are stronger shaft/hub assemblies avaliable?
 
Same thing applies for the 904 OEM Input... I've seen them break in 11 second cars but not break in 10 second cars. You can be on the fence real easy with a 904. Going from a 500hp 904 to an 800/1000hp 904 is a huge jump in price when adding 300m shafts, billet drums and rollerized geartrain.

The thing with the 904 is, you cannot just add a billet fwd clutch drum and 300m input shaft as it has a bearing that has to ride in the pilot of the 300m output shaft. So the input and output shafts for the 904 must be purchased together

Building a 904 now for 800+hp, even though he won't make that much power yet.. but he has room to grow.

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1967 Cuda said:
Hello Chris......I did want to pick your brain in regards to low/reverse band applied in 1st gear in a 727 transmission. I have two different 727 transmissions with reserve manual valve bodies and one have the low/reverse bands applied in 1st gear and the other does not. I am in the process of building a street strip 68 Dart with a 470 that should be around 600 hp and 600 tq. To be honest, I kind of like how the 727 without the low/band applied in 1st gear drives as there is no engine braking below 20 mph and I have made the mistake of accidentally down shifting the transmission with low/reverse band applied in 1st gear coming up to traffic lights on the street, which wasn't fun as it locked up the rear wheels. I have read the issues associated with not having the low/reverse band applied in 1st which is putting more strain on the sprag which can lead to failure. (At least that is what I have read). My question to you is, is there a way to safely have the low/reverse band not applied in 1st gear as to not have engine braking in 1st under 20 ish mph, or do I just need to deal with this type of operation so I can be safe with launching the car in 1st when I do go to the track. Thank you in advance for your insight!
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Nothing against Chris, but John Cope has a new feature in his valve bodies called a Tesla valve. It gives you low band apply, but prevents that sudden lockup of the rear wheels caused by the band coming on when you down shift to 1st gear. AFAIK an industry first for the torqueflite.
 
Duster346 said:
I was one of the first members of this site when Adam started it in the early 2000's. I've been off this forum for the last decade or so, as life gets in the way of things we'd like to pursue further, unfortunately.

My quickest BB727 has been in the 7-teens at just under 200mph and my quickest SB727 has been in the 8.50's naturally aspirated at 6000 feet elevation. I am not here to win anyone over or make money. I don't need this site to make money-- however, feel free to let me know if you have any questions about your build. I've given free advice with no sales for several decades and I'm fine with it. I won't advertise my website, as that is against site rules now, but I've helped several on here with advice or parts for quite some time.

As always, good luck with your racing program!

Chris Andrews
Andrews Racing Transmissions
Castle Rock, CO

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I saw a post on this site a while back where you said that the new 30 element sprag for the 904 does not work because you saw or had a failure. Can you elaborate on what you meant by doesn’t work.
 
Duster346 said:
Same thing applies for the 904 OEM Input... I've seen them break in 11 second cars but not break in 10 second cars. You can be on the fence real easy with a 904. Going from a 500hp 904 to an 800/1000hp 904 is a huge jump in price when adding 300m shafts, billet drums and rollerized geartrain.

The thing with the 904 is, you cannot just add a billet fwd clutch drum and 300m input shaft as it has a bearing that has to ride in the pilot of the 300m output shaft. So the input and output shafts for the 904 must be purchased together

Building a 904 now for 800+hp, even though he won't make that much power yet.. but he has room to grow.

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I’ve made a pin out of Thompson shafting to use a billet 300m input shaft with a stock output shaft. The factory pin is just pressed into the output shaft. I simply pull that out, press in a piece of Thompson that had a hole drilled through for oil, and buy the selective
Thrust bearing assembly. FYI
Off course a 300m output shaft would be much stronger, but it is doable with just the billet input.
 
May I ask a question I am needing answers to soon this spring? About my 60 thousand mile transmission in my van 904 I believe, reverse just stopped working, I have been told it can be fixed while its in the van.
My question is what broke, where is it ? What is it called?

Thank you guys, hope I didn't interfere with any direction on this thread.

Man on the hill in northeast Arkansas, memike

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memike said:
May I ask a question I am needing answers to soon this spring? About my 60 thousand mile transmission in my van 904 I believe, reverse just stopped working, I have been told it can be fixed while its in the van.
My question is what broke, where is it ? What is it called?

Thank you guys, hope I didn't interfere with any direction on this thread.

Man on the hill in northeast Arkansas, memike

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Make year and model
 
Duane said:
I saw a post on this site a while back where you said that the new 30 element sprag for the 904 does not work because you saw or had a failure. Can you elaborate on what you meant by doesn’t work.
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Sure. If the assumption is that the 30-element dog bone style sprag is going to handle a lot more power, say in a big tire, tube chassis car, it's not. So, to say it doesn't work, may have been a slight error on my part. It may work in your (just an example) 600hp, small tire drag car--just the same as the 10 element OEM 904 sprag. I know who developed and co-developed that sprag, and it is not my intention to mud-drag or smear those folks. It is my intention to advise people of the possibility of failure if purchasing that sprag for a certain application.

The factory pin is just pressed into the output shaft.
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I am aware of this.

One of the major manufacturers of 300m shafts will not sell a 300m input without the 300m output for a 904 or 727, FYI.
 
If the problem is in the reverse servo, then possibly yes, if it isn't a double wrap band; those are tougher. But it's probably not a 904 but a 727, which didn't come with a double wrap band; making the servo easier to get to.
 
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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?
 
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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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.
 
Duster346 said:
Sure. If the assumption is that the 30-element dog bone style sprag is going to handle a lot more power, say in a big tire, tube chassis car, it's not. So, to say it doesn't work, may have been a slight error on my part. It may work in your (just an example) 600hp, small tire drag car--just the same as the 10 element OEM 904 sprag. I know who developed and co-developed that sprag, and it is not my intention to mud-drag or smear those folks. It is my intention to advise people of the possibility of failure if purchasing that sprag for a certain application.


I am aware of this.

One of the major manufacturers of 300m shafts will not sell a 300m input without the 300m output for a 904 or 727, FYI.
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Yes I know who that is.
 
Duster346 said:
Sure. If the assumption is that the 30-element dog bone style sprag is going to handle a lot more power, say in a big tire, tube chassis car, it's not. So, to say it doesn't work, may have been a slight error on my part. It may work in your (just an example) 600hp, small tire drag car--just the same as the 10 element OEM 904 sprag. I know who developed and co-developed that sprag, and it is not my intention to mud-drag or smear those folks. It is my intention to advise people of the possibility of failure if purchasing that sprag for a certain application.


I am aware of this.

One of the major manufacturers of 300m shafts will not sell a 300m input without the 300m output for a 904 or 727, FYI.
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So you are saying that the 30 element sprag
Cannot handle any more torque that the stock sprag ? What does the application have to do with it ? I am assuming a transbrake
Or manual shift valve body with low band apply. Why would the application make a difference?
 
Duane said:
I saw a post on this site a while back where you said that the new 30 element sprag for the 904 does not work because you saw or had a failure. Can you elaborate on what you meant by doesn’t work.
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It’s “better” but not foolproof.…. Kind of like it’s 727 counterpart. Still good insurance
 
Duane said:
Probably the low reverse servo flipped in the bore. If it’s the piston, then yes can be fixed in the car as long as the band is still good.
Do you have 3rd gear ok ?
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Yes I do, the owner continued to drive it to the hills, being careful never to park anywhere needing reverse, if he did he parked up hill so it could roll backwards.
Lower reverse servo flipped, :thumbsup:
Thank you so much Duane, I will do some searching and learn what I need to do, you gave me the information I needed to continue forward to repair this reverse problem.
 
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memike said:
Yes I do, the owner continued to drive it to the hills, being careful never to park anywhere needing reverse, if he did he parked up hill so it could roll backwards.
Lower reverse servo flipped, :thumbsup:
Thank you so much Duane, I will do some searching and learn what I need to do, you gave me the information I needed to continue forward to repair this reverse problem.
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A body said:
It’s “better” but not foolproof.…. Kind of like it’s 727 counterpart. Still good insurance
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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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