904 to 727 upgrade.

Duane said
The info that I have always heard about the performance improvements of a 904 over a 727 when both equally built are about
.15 faster in the quarter mile. To me the real benefit of the 999 version is it had all the best beefy parts and the 2.74 low gear. The planetaries are all steel and both are 4 pinion. The front drum in the late 80,s model came with the 5 clutch front drum. Also a better thrust washer design between the input and output shaft. It also uses a 4 clutch rear drum, double wrap low reverse band. No one seems to pay attention to these because of the lockup feature, but the internals had all the best stuff in them.
The first one I converted, I used a 2 ball stator and an input shaft from a slant trans. To use the 5 clutch front drum on the 2 ball stator requires machining on a lathe to cut a bevel to clear the wider drum. There is a .060 though difference on the seal ring diameter
Between a 2 ball stator and a 3 ball lockup stator. So to use a lockup 4 clutch forward drum on a 2 ball stator also requires machining the bore in the stator to 1.560 from 1.500.
If you put a non lockup forward clutch into a lockup stator, it will bolt together without any machining, but the .060 thou difference in sealing ring diameter will cause a big hydraulic leak and you will not get any forward motion.
I converted my first and only lockup 999 to non lockup by doing this machining. It worked fine.
However years later I am questioning whether I really needed to use a 2 ball stator. I am currently reviewing the hydraulic passages of an
A500 overdrive trans that a friend donated to me. It has a larger higher volume pump gear with the "d" drive on it. The gears are also only 11 lobes which are a higher pump volume. The front drum
Is unique to this stator with 2 different diameter bushings versus the regular one bushing. This drum and pump stator assembly could be used in a non lockup as long as those parts stay together.
To answer your question about the input shaft, yes you could use the input shaft from any non lockup 904-999 for the conversion.

My current 904 in my drag car has a 2.74 factory steel rollerized 4 pinion front planetary, rollerized steel 4 pinion rear planetary, the new 1,000 ft pound rear sprag from ati, red lined double wrap low reverse band with a&a solid low reverse servo, double rollerized output support, 1.75 inch wide red line 2nd gear band, with double
Ring billet servo, aluminum 4 clutch rollerized 4 clutch drum with 5 thin clutches, 4 clutch lockup forward clutch into 2 ball ported stator with a&a big lug heavy duty race pump gears, with a turbo action
4600 pro series converter with the optional thick walled drive hub,
and new transact pro comp nitro brake with safe neutral. Billet ati input shaft and lightened rollerized sunshell.
Overkill for what I need, but I only paid for parts and all the machining and labour I did my self.
But I am looking at an easier way to just do a basic conversion to non lockup without all the machining. I am not 100% sure but I think you can still use a 3 ball stator. Just change the input shaft and the valve body to non lockup. There should be some pics in my profile of my trans.

After some investigation this week, I think I have figured out a way to convert a lockup trans to non lockup while still using a 3 ball lockup stator and requires no machining.
As far as I can tell the 3 ball stator uses a 3rd oil passage and an additional sealing ring on the input shaft that is used to operate the lockup converter. The 2 ball stator simply does not have this 3rd passage drilled because it is not required.
There are no differences on the case.
Although this method may not be the cheapest way to do it, it should work. The main parts to be changed are the valve body, the torque converter and you would have to buy a 27 spline, yes 27 not 26 input shaft that a&a trans sells. This is a 300m billet input shaft specially made for the lockup trans. Although it says in the catalogue that it is a 2 ring, it also says it is 27 spline so that it can be used with common non lockup aftermarket converters. The reason that you cannot use the standard 1 ring input shaft is that the bushing and sealing ring surfaces in the lockup stator are placed differently to allow the second sealing ring. Therefore the two shafts are dedicated to there respective staters. The a&a 2 ring shaft is still designed for for the lockup stator but operates as a non lockup with the aftermarket converter and valve body.
This shaft is not cheap, but would allow the conversion to non lockup without any custom machining. It also appears that an A500 flat drive pump and stator assembly could be used with this shaft as well as long as that front drum and stator stay together. Or the other option one could do is use the flat drive pump and gears with any 904 build as long as the converter has the appropriate drive on it. I have not tried this way of converting to non lockup, so don't hold me to it, but from what I can see it should work.
This method would allow a late eighties lockup trans which had all the best heavy duty parts for v8 use to be used as is with just an input shaft, converter change and valve body change.