Trans Shift point question??
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Logistics Pro
Joined: Oct 2004
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From: FL
Trans Shift point question??
Hello and merry christmas/happy holidays to all!!! - just got a quick question about shift points in a psd.... i have a 97 with an auto trans (4 speed w/ TC lockup) and 4:10 gears.... my question is this.... the first 3 gears go firm and fine all the time, usually shifting at about 1500-1750 rpms, (under slow acceleration) but 4, (or overdrive) never hits till about 2000 rpm's, at 35MPH. Then the TC locks up and everything is fine.... my question is this.... is it normal for the trans to wait till 2grand to shift into overdrive? i was thinking it is normal, due to the low 4:10's although i'm not 100% sure..... I mean the truck has enough torque to pull at 50RPM's in overdrive, so why would the pcm delay the shift till 2000 Rpm's???? (well maby not 50, but close!!) any input would be great!!! thanks!! -Robb
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Joined: Feb 2002
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From: Bonney Lake, WA
Depending on the box code of your truck, the last shift you're feeling might not be the shift into OD, but the torque convertor locking. I've got a '97 code in my chip, TDE1, and my shift sequence is: 1-2, 2-3, tc lockup, 3-4. My torque convertor locks at 35mph, and the shift into OD happens at 42mph. Both of these are assuming light acceleration, of course. The shift points rise with the weight of the right foot.
If you've got a different box code, your shifts might have the last two "shifts" reversed from my example. If you let off the throttle prior to the last "shift", do the rpms drop down to near idle speed, or do they hold near the rpm prior to letting off the throttle? If they drop substantially, it's likely the tc hasn't locked yet, and the final "shift" is actually the tc locking.
If you've got a different box code, your shifts might have the last two "shifts" reversed from my example. If you let off the throttle prior to the last "shift", do the rpms drop down to near idle speed, or do they hold near the rpm prior to letting off the throttle? If they drop substantially, it's likely the tc hasn't locked yet, and the final "shift" is actually the tc locking.
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Logistics Pro
Joined: Oct 2004
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From: FL
The first three gear shifts are all very similar... then into the last "gear/ tc lock-up" it goes into what i think is overdrive... and then the tc locks up, so i believe that it is the reverse of yours Quad.... if i let off the throttle after 3rd, and before the next gear, the trans doesn't shift at all, the truck just slows down.... and the "4/tc lockup" can not be isolated... they happen almost similtaniously.... even when slowing down... the tc doesn't unlock and stay in OD, it goes stright to third.... which can make for quite a jerkey ride from about 33-37 mph on side roads.... so i was wondering it if this is normal... or not?? also is it normal for the pcm to delay the last 2 " shifts (od+TC lockup)" till 2000 Rpm's?? The truck waits in third to make these last two changes......- Thanks for the help so far Quad!!
Last edited by Robbgt; Dec 25, 2004 at 06:51 PM.
