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Old 09-14-2005, 10:22 PM   #1
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Default Transmission Shifting

Maybe someone can explain this to me..

With a stick, you depress the clutch, thus removing load from the engine. If you were to stay on the gas the engine would just free rev into unsafe RPM territory. How do automatics shift so fast without removing power transfer? Like when the car shifts the RPMs don't raise a bit, but the transmission engages immediately [at least the case on the cutlass.. certainly not the bonneville anymore :(]. I understand how the transmissions slip and all, but with that slip comes less load, less load equates more RPM, which I don't have. So how does this work?

Btw, a little update for everyone on ol' pearly'* transmission. http://www.bonnevilleclub.com/forum/...ic.php?t=40550
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Old 09-14-2005, 10:55 PM   #2
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the PCM controls the engine and the trans shfits.....if you ever ride in a Daimler product vehicle and go WOT you can feel the car pull the timing and fuel as the car shifts to protect the trans
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Old 09-14-2005, 11:44 PM   #3
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Not in the hydraulic pre-92s. I don't think there is any timing retard at shift points, because the ECU doesn't know when it'll shift, just after it does. I just want to know how the RPMs are consistent, and the transmission drops out of gear and into another without the RPMS increasing. Even if this happened at split second speeds, you could still see some sort of RPM increse.. but there is none.
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Old 09-14-2005, 11:53 PM   #4
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oh...i though you were just talking in general....

remember everything is clutches and bands for constant friction, and the engine dosent free rev
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Old 09-14-2005, 11:56 PM   #5
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The TV cable prolly has something to do with it......I would assume.
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Old 09-15-2005, 12:05 AM   #6
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i too have wondered this very thing. the taurus does the same thing. when its cold, it will stay between gears for 3 seconds. the rpms hold, yet the power output drops off <like it is all disengaged>. but i doubt it is pulling timing because it pulls like crazy just as it drops into second. i too wonder what happens to all that power. and what about those old cars that arent smart enough to pull timing?
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Old 09-15-2005, 07:50 AM   #7
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Exactly, the cutlass [86] is carburated and has a distributer. It is electronically controlled, but the ECU in that thing is hardly an ECU. I keep wondering why the carb really sucks with light throttle and works real well with higher throttle [ECU problems]. Oh well, still doesn't answer my question .

Just for clarification, this would be on a carburated and a points-style distributer equiped car. Something unable to adjust timing.
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Old 09-16-2005, 07:04 PM   #8
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Old 09-16-2005, 10:13 PM   #9
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I don't know if this will give you your answer but I found this an interesting read.

http://auto.howstuffworks.com/automa...ansmission.htm

It has multiple page so just keep on clicking Nex Page
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Old 09-16-2005, 11:09 PM   #10
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Sorry I did not go to the how stuffworks page but I believe i remember seeing in a couple of places that nearly all of the GM Automatics do not ever leave gear but hits 2nd gear and then disangages first

So no free rev and not timing or fule being pulled
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