904 to 727 upgrade.
I've heard a lot of silly talk about "parasitic drag"...Claims that the 904 saves tons of horsepower over a 727; same with a C4 over a C6, and a th350 over a th400. But in every case, either the kd wasn't properly set up after the change, or the original large converter was used.
Duane, isn't the non-lockup input shaft from something beside a slant six compatible to eliminate the lockup feature? I'd love to see a write-up on using an eighties 999 or whatever with the five plate dual bushed direct drum, wider band, and low gear first; with the retrofit non lockup feature. Along with the pump gear conversion to eliminate the converter lugs.
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.
