I have a question regarding the way the 727 in my car (440+6 and 4:10 rear) shifts. When taking off from a standing start at just a normal rate of acceleration (like say from a stop sign in 25 mph zone), the trans. shifts from first to second pretty quickly. When it shifts from second to third, there is a strong down surge (for lack of a better way to put it) that actually makes the upper half of my body lurch forward. The quick first to second shift doesn't really bother me that much but the down surge from second to third is getting old. Can someone tell me what would cause this to happen? I might add, the down surge doesn't happen if I take off at a higher rate of acceleration.

the forward surge you are feeling is an interuption in the acceleration caused by overlap (2 items "on" at the same time that should not be) that is slowing you down. A shift kit helps with that among other bennies from it but (#1) wait for Kunkel (& others) to further advise

2 to 3 overlap was designed in our trannies in an effort to make a smoother, less noticeable shift for the non-performance buying public. And is something us performance guys have dealt with forever. It is much more noticeable at light throttle.

The only real way to deal with it (as far as I know) is to put a restrictor in the port that feeds high gear. That slows down the filling of that clutch pack thereby slowing high engagement and minimizing the overlap. The size needed varies some, and takes some trial and error to get just right. But on my trannies, an orifice in the .090" is usually close.

The biggest hassle is that you have to drop the valve body to get at the port. If you decide to do this, there are a couple of different ways to make the restrictor and several threads with pics on how to do it.

Another way to mitigate the 2-3 overlap is to loosen the kickdown band adjustment a little bit.

Wow. How did you guys get to 2-3 overlap as the problem based on his description. A couple of things came to my mined, and none 2-3 overlap flash?????

Downward surge seems contracting in of itself.

"Another way to mitigate the 2-3 overlap is to loosen the kickdown band adjustment a little bit."

I am not all that knowlegable regarding automatic transmissions. Is what you are suggesting something I can do myself or would I need to take it to a trans. shop?

You can definitely do it your self. its a oddball shaped male nub with a 3/4" (iirc) locknut and the "kickdown" one is either the one on the outside of the trans case or the one inside the pan (find out which). Hold the nub still with some vice grips and loosen the locknut then loosen (CCW) the nub however much the guys here will advise you to do so then hold it still at that new position & tighten the locknut

The 2-3 shift in a TF involves the releasing of the kickdown band and the application of the front clutch; when the clutch applies before the band is sufficiently released there is an overlap when both components are partially applied. As Dave stated, a certain amount of overlap is necessary to prevent engine rpm flare-up on the shift but excessive overlap causes the nose dive situation.

This is more pronounced at low speed/low throttle because the car doesn't have the momentum to "drive through" the resistance caused by the excessive overlap. At higher speeds the overlap is still there but the car's momentum will make the overlap less noticeable.

Yes, I just don't think that is what he is describing. Don't know though.

Bit of a hijack but... Does this apply to the a518 too?