| Re: [GMCnet] tranny kick down switch [message #153989] |
Wed, 21 December 2011 20:28  |
Gary Casey
Messages: 448
Registered: September 2009
Karma:
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Senior Member |
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In spite of how it feels during a full throttle upshift, I'm sure it will not "destroy itself." However, downshifting from 3rd to second manually is significantly harder on the transmission than downshifting automatically by way of the detent ("kickdown") switch. When downshifting manually the second overrun band is engaged and it will try to pull the engine up in speed. When doing a full throttle automatic downshift the third clutch is simply released and the engine is merely allowed to increase in speed until the second freewheeling clutch engages - very gentle compared to trying to jerk the engine up with the second band. The second gear band is very, very fragile and it doesn't take a lot of high speed downshifts to burn it up. When I need to downshift I'll go to full throttle momentarily to trigger the downshift and then move the lever to the "S" position to hold it in second. Avoid manually forcing the downshift unless it is really
necessary. The upshift to third is no different whether selected manually or allowed to happen automatically.
A manual 1-2 shift, however is a totally different animal. When in either S or L the transmission line pressure is increased to the maximum - usually about 150 psi. So the manual 1-2 shift, even if done at very light throttle, is done at maximum line pressure. That can really jerk, but it still won't destroy the transmission. One way to "trick" it: With the transmission selector in L and the transmission in 1st, go to full throttle and immediately shift to D, back off a little on the throttle, allowing it to shift to second. Immediately pull the lever back into S, holding it in second.
I've seen some "shift kits" that make logical changes in the shift calibration to speed up the shifts without making them too harsh. But I've seen others where the builder seemed to think that if some is good a lot more is better. These guys will often throw away check balls that are there to control shifts, leaving the clutches with no fill restrictions at all. Just doesn't make sense. And then they will increase the pressure regulator spring force to the point that the shifts are impossibly harsh. Doesn't help the transmission, doesn't make it run cooler - all it does is make it obnoxious.
Just my opinion.
Gary Casey
I unplugged my kick down and only pull it into super manually. My tranny has a shift kit in it so it shifts harder then stock. On a hill it down shifted OK but at times the up shift was too violent. I unplugged it to save the tranny from destroying itself.
--
Roy Keen
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