Rebuild 904 or swap for 727?
I don't like the low band apply cuz it complicates the 1-2 shift. Instead of just applying the intermediate band for second, it has to release the low band at the same time; who needs that overlap; (might lose .25 seconds..). That's why I design mine to be raced in "D". Take off in first gear with the lever in "D" and the low band isn't applied.PS You have to remember Duane, my posts aren't written for you, but to help the guy who's working on his own car and needs some input as to how to build a car on a budget. So I'll argue with you and let them make their own choice, based on the info that comes out of our discussions. Everybody already knows that the only thing that beats cubic inches; is cubic dollars, but when it comes to Chrysler's best trans, just stick with the 727 whenever possible and move on to things on your car that really do need upgrading.
I like this post and I will tell you why. You brought up an area of the Torqueflite that I don't have experience and that is the low band apply and how it complicates the 1-2 shift.
I bought a tranzact brake with low band apply.
All Torqueflite brakes apply the band when the brake is on.
All of them. It's what happens to the band after you let go of the button. Here is where there are differences among different companies. It is hard to get the secrets from the differing manufacturers.
Turbo action years ago touted his timed release of the band.
In other words they don't shut the band off right away because the theory goes that if your slicks were to hook and then spin, while still in first gear. This spin in first gear can still damage the sprag, but as you have said, you don't want to mess up the 1-2 shift.
In the last say ten years or so we started to see the manufactures release brakes with a billet aluminum bottom valve body.
I could not understand the reason for this.
Then later we started to see billet aluminum brakes with the band on right until you pull the shifter to second gear. No timed release.
The manufacturers claimed a clean shift. How can this be.
I have one of these now.
In one of John Cope YouTube videos, he explains that when you buy one of his low band apply valve bodies, brake or manual shift,
You must also buy his rear servo kits for it to work right.
According to John these aluminum billet valve bodies have custom
Machined oil passages that allow the fluid to move faster and the servo is solid with a much higher return spring pressure to shut the band off really quick. On top of this, he recommends a band adjust
On a 904 with double wrap band of only 2.5 turns out from 72 inch pounds. It seems too tight to me and the factory manual calls for 4 turns.
I asked John about this band setting, and all he would say is 4 turns is too loose, but he won't explain why.
I am speculating that for a drag car only, this tighter setting also speeds up the shut off of the band to get a clean 1-2 shift but I don't know for sure.
What do you think ?
