http://www.txchange.com/transgo.htm
http://www.automedia.com/Auto_Trans_Shi ... 050201sk/1
http://racingarticles.com/article_racing-77.html
http://www.transgoperformance.com/
http://www.transmissioncenter.net/Shift_Kits.htm
http://www.youtube.com/watch?v=6Svl0fDl1qI
Originally Posted by TNprogrammer
Every time I see someone talking about rebuilding their auto trans, they mention putting a shift kit in it. Now, I've heard people talk about shift kits in transmissions all my life, but never really cared about what they did. Can someone explain to me exactly WHAT a shift kit really does and why you would want one? Thanks.
rjent
it is a little complicated but not too bad. An automatic has a gear set called a planetary set that is constantly in mesh. We control the ratios by changing how each part of the planetary set is manipulated. Without going into full detail the forward or direct clutch is applied in first gear which spins the sun gear on the primary planet set and there is a whole reaction in the rest of the gear set from there. As that sun gear is spun (direction of engine rotation) the ring gear on the planet set spins backwards. Second gear happens when we stop that ring gear from spinning making it stationary. The faster we can apply the holding device (band or clutch) to hold the ring gear the more solid and less slippage the shift is. Third gear happens when we apply the high reverse clutch (the one closest to the front of the tranny) which basically "locks up the planet set" making a 1 to 1 input to output.
A shift kit changes oil pressure (line) and changes the flow to those clutches and bands to create a far more efficient transmission. We control the different oil flow/pressure by drilling out holes in the valve body separator plate, changing springs on the pressure regulator and the shift valves. It is all a balance of keeping the transmission shifting at the right time, but spending less time changing from one gear to another!
So, in laymens terms, I have always thought that it basically made the transmission shift more quickly from one gear to another, or spend less time in transition from gear to gear. Am I close?
That is exactly right!
rjent
A "banded" three speed (C4, C6 Fords, torqueflights etc) use a band as the second gear holding device. That band has to release as the high/reverse (3rd gear) clutch is applying. There is an overlap of time when the transmission is in 2nd and 3rd at the same time . If the band releases too soon, it goes back into 1st (flares in RPM) briefly before the HR clutch applies. If the HR clutch applies before the band releases you go into a binding lockup briefly. The GM tranny ie 350 and 400 THM's don't us a band for second gear. They have a clutch spragged so when the HR clutch applies the stationary clutch (ring gear) simply spins away on the sprag. The sprag has the down side of weakness, but eliminates the "overlap"
So banded trannys have a whole different approach to a shift kit than GM does. But the bottom line is making the tranny shift from one gear to the next quicker and more efficiently!
http://www.automedia.com/Auto_Trans_Shi ... 050201sk/1
http://racingarticles.com/article_racing-77.html
http://www.transgoperformance.com/
http://www.transmissioncenter.net/Shift_Kits.htm
http://www.youtube.com/watch?v=6Svl0fDl1qI
Originally Posted by TNprogrammer
Every time I see someone talking about rebuilding their auto trans, they mention putting a shift kit in it. Now, I've heard people talk about shift kits in transmissions all my life, but never really cared about what they did. Can someone explain to me exactly WHAT a shift kit really does and why you would want one? Thanks.
rjent
it is a little complicated but not too bad. An automatic has a gear set called a planetary set that is constantly in mesh. We control the ratios by changing how each part of the planetary set is manipulated. Without going into full detail the forward or direct clutch is applied in first gear which spins the sun gear on the primary planet set and there is a whole reaction in the rest of the gear set from there. As that sun gear is spun (direction of engine rotation) the ring gear on the planet set spins backwards. Second gear happens when we stop that ring gear from spinning making it stationary. The faster we can apply the holding device (band or clutch) to hold the ring gear the more solid and less slippage the shift is. Third gear happens when we apply the high reverse clutch (the one closest to the front of the tranny) which basically "locks up the planet set" making a 1 to 1 input to output.
A shift kit changes oil pressure (line) and changes the flow to those clutches and bands to create a far more efficient transmission. We control the different oil flow/pressure by drilling out holes in the valve body separator plate, changing springs on the pressure regulator and the shift valves. It is all a balance of keeping the transmission shifting at the right time, but spending less time changing from one gear to another!
So, in laymens terms, I have always thought that it basically made the transmission shift more quickly from one gear to another, or spend less time in transition from gear to gear. Am I close?
That is exactly right!
rjent
A "banded" three speed (C4, C6 Fords, torqueflights etc) use a band as the second gear holding device. That band has to release as the high/reverse (3rd gear) clutch is applying. There is an overlap of time when the transmission is in 2nd and 3rd at the same time . If the band releases too soon, it goes back into 1st (flares in RPM) briefly before the HR clutch applies. If the HR clutch applies before the band releases you go into a binding lockup briefly. The GM tranny ie 350 and 400 THM's don't us a band for second gear. They have a clutch spragged so when the HR clutch applies the stationary clutch (ring gear) simply spins away on the sprag. The sprag has the down side of weakness, but eliminates the "overlap"
So banded trannys have a whole different approach to a shift kit than GM does. But the bottom line is making the tranny shift from one gear to the next quicker and more efficiently!