4L65, sliding 1-2 shift.
10-12-2004, 09:24 AM
#1
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4L65, sliding 1-2 shift. Good morning...
I'm getting an occasional slide on my 1-2 upshift.
It will only happen if I give the motor moderate throttle, and bring the RPM's up over 2,500rpm or so. If I accelerate at a "normal" pace, it shifts just fine with the stock firmness.
I had this issue about three times over the last two days, but was not able to duplicate it this morning. I had my laptop handy, so I scanned... I had two 1.0 second 1-2 shifts, but they "felt" good. They had authority.
All other shifts are just fine.
I have no internal tranny mods done. I do have a lot of programming done to shift points, and TM is reduced to 300ft/lbs on the 1-2, and 350ft/lbs on the 2-3 shifts. Shift pressure has not been touched. I've done a moderate amount of towing, maybe 500miles with a 5,000lb trailer.
Fluid level is good, fluid color/odor is fine. A few drops of fluid on a clean paper towel didn't leave any rings or residue. Truck has 26,000 miles.
The 1-2 accumulator in this tranny is plastic. (I don't know if it's the same in the f-body 4L60's). I guess this has a tendency to crack if used with a shift kit. I've had two people tell me that they most likely this has cracked on me... but I'm surprised if that's the case with my tranny being stock.
I've been told to replace the accumulator, but throw a TransGo shift kit, (and the Corvette servo) in while I have the pan off.
What do you guys think?
Any chance it was just a hiccup in programming or throttle position or something?
I'm getting an occasional slide on my 1-2 upshift.
It will only happen if I give the motor moderate throttle, and bring the RPM's up over 2,500rpm or so. If I accelerate at a "normal" pace, it shifts just fine with the stock firmness.
I had this issue about three times over the last two days, but was not able to duplicate it this morning. I had my laptop handy, so I scanned... I had two 1.0 second 1-2 shifts, but they "felt" good. They had authority.
All other shifts are just fine.
I have no internal tranny mods done. I do have a lot of programming done to shift points, and TM is reduced to 300ft/lbs on the 1-2, and 350ft/lbs on the 2-3 shifts. Shift pressure has not been touched. I've done a moderate amount of towing, maybe 500miles with a 5,000lb trailer.
Fluid level is good, fluid color/odor is fine. A few drops of fluid on a clean paper towel didn't leave any rings or residue. Truck has 26,000 miles.
The 1-2 accumulator in this tranny is plastic. (I don't know if it's the same in the f-body 4L60's). I guess this has a tendency to crack if used with a shift kit. I've had two people tell me that they most likely this has cracked on me... but I'm surprised if that's the case with my tranny being stock.
I've been told to replace the accumulator, but throw a TransGo shift kit, (and the Corvette servo) in while I have the pan off.
What do you guys think?
Any chance it was just a hiccup in programming or throttle position or something?
10-12-2004, 09:38 AM
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It may be there are regions where you have more engine
(* converter multiplication) torque than you have shift
pressure to hold. You may want to log the Delivered
Torque - Trans PID, input & output shaft speeds (so you
can take the ratio and see any shift flare / settling)
and see if there are any "bumps" where you have too
soft a shift action. The Delivered Torque - Trans is the
torque index for the shift pressure tables I believe (not
the engine torque). If you lower your shift adaptation
time settings the PCM may just learn not to "slide" on
its own but upping the shift pressure in areas where you
feel it, wouldn't hurt.
(* converter multiplication) torque than you have shift
pressure to hold. You may want to log the Delivered
Torque - Trans PID, input & output shaft speeds (so you
can take the ratio and see any shift flare / settling)
and see if there are any "bumps" where you have too
soft a shift action. The Delivered Torque - Trans is the
torque index for the shift pressure tables I believe (not
the engine torque). If you lower your shift adaptation
time settings the PCM may just learn not to "slide" on
its own but upping the shift pressure in areas where you
feel it, wouldn't hurt.
10-12-2004, 12:12 PM
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Cool stuff, I'll scan it tonight...
I'm a little hesitant on chaning any tuning parameters at this point. I've been running this tranny programming for at least a month now with no slides...
I lied about the 1.0 second shifts - i just noticed those were from 'logging glitches' in HPT. The slowest I scanned was .5sec, which is in spec of the ".6 desired" 1-2 upshift.
I'm a little hesitant on chaning any tuning parameters at this point. I've been running this tranny programming for at least a month now with no slides...
I lied about the 1.0 second shifts - i just noticed those were from 'logging glitches' in HPT. The slowest I scanned was .5sec, which is in spec of the ".6 desired" 1-2 upshift.
10-12-2004, 02:12 PM
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Well, I desire 0.15 second upshifts and have gotten away
with running 0 time values for over a year, previously
(Predator does that if you tell it -20%). So you've got plenty
of room to play.
with running 0 time values for over a year, previously
(Predator does that if you tell it -20%). So you've got plenty
of room to play.
