Rebuild 904 or swap for 727?
Old thread I know. But the actual amount of "parasitic drag" in a 727 amounts to less than 1/4 second in the quarter mile. The reason people believe the bigger transmissions have so much drag (chevy, ford, mopar) is because when the 904 is swapped out for a 727, the original 727 converter is used, and it usually has a lower stall. Then they don't have the kickdown set up and adjusted properly (thinking they'll just shift it manually) but it shifts too soft and the shifts are longer without the kd right. And good luck finding somebody who can do a performance build on a 904; much less any automatic. They throw a kit in it and call it good. And don't get me started on these "performance" trannys for $2k and up; most only have four direct frictions. Chock full of their own trick (expensive) specialty parts. The weak point on ALL the old three speed automatics is third gear.
I am disagreeing with the post!
Chrysler did back-to-back testing in the '70 and when both 727 and 904 were built to the same level and converters were configured the same, the ET difference was about .15, which is still a lot when looking for ET in a restricted class racing environment.
* The original 727 converter
can not be used in a 904. Even if it could be, it wouldn't affect the stall/flash.
* If the kick'down and automatic featured are retained, they simply "should" be adjusted properly. If somebody doesn't do it right, it's not the transmission's fault. But most
race cars use a RMVB.
* 904's don't blow up like a 727 when the sprag gets damaged, improper burnout, driveline breakage, etc.. That's a big benefit right there.
* There are obviously many people who can build a good 904. Aftermarket internals are even put into 727's behind Hemi's & big blocks.
* While some of the specialty $2K 904's get the job done. A lot of the price goes into aftermarket parts and lighter weight. Often some durability is sacrifices for a few more hundredths of ET. The trans just needs to be rebuilt more often. That's the racers choice.
