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Harsh Downshifts - is there a fix?

njk4o5
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chrispassas21 Enthusiast

chrispassas21

Posted
Posted
im going to try for the lemon law as hard as I can. im sick of having to leave work early to take this shitbox to the dealer who cant fix it. im going to try to legally fcuk them as much as possible

What ever happened with this?


2015 Silverado LT Midnight Edition
4.5” CST suspension lift
Sent from my iPhone using Tapatalk
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Jwc
Jwc

So does anyone think hard down shift is what could have caused my torque converter to come apart?

MGIG
MGIG
njk4o5 Enthusiast

njk4o5

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Posted

The lemon law is a PITA to do. I probably had to bring my truck back and forth to the dealer 15 times but finally got a new trans out of them. Truck is out of warranty now and at 113k miles. I put 35" tires on it too and so far the shifting is back to normal.

  • 9 months later...
Brandon Romero New Member

Brandon Romero

Posted
Posted

I have a 2015 Chevy Silverado LT with 96,000 miles on it . I’ve been noticing the harsh downshifting as well , I bought a diablo tune and set it to performance 93 while also turning off my AFM . Hoping this will fix all the harsh shifting I’ve been experiencing with the truck . It helped a little but not really . Still get weird shifting from the first 3 gears up and down . I did this only because the dealership told me the truck was supposed to shift like that .. I’m in fear of my trucks tranny taking a dump on me shorty after I lift my truck . Past trucks drove 10x smoother 

  • 1 month later...
  • 2 years later...
MGIG New Member

MGIG

Posted
Posted
On 4/25/2017 at 4:01 PM, Dunc said:
On 4/25/2017 at 2:24 PM, njk4o5 said:

theres no way this is normal. my truck does it intermittently 75% of the time. the other 25% of the time it drives as it should

This is a normal symptom of the GMC tranny. You can push and hold tow haul for three seconds and it will shut the gear brake off and it helps tremendously! Also try using Diablos Preditor 2 Tune, seems to help.  Good luck 

 

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  • 10 months later...
bubbanbrenda Enthusiast

bubbanbrenda

Posted
Posted

turning off hill decend helps a lot for my 2014, but still not a cure. I think the hill descend feature should be off my default below 30-40 MPH would be a good idea.

  • 3 months later...
Vatech New Member

Vatech

Posted
Posted

Just bought a used 2014 sierra z71 doing exactly the same a hard downshift when almost stopped smooth all other times  going to the dealer tomorrow to have it checked didn’t feel normal for sure!

  • 5 months later...
JeremyGray New Member

JeremyGray

Posted
Posted

I got a new transmission at about 170k. Never had a hard down shift. Now I have 50k on the new transmission and today it started down shifting real hard. Especially from 2nd to 1st. Before you never really noticed it even down shifted. One time today it almost chirped the tires. 

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      Thanks newdude!  By the time manual selection is needed, I'm probably too much of a control-freak to depend on the transmission sensing braking to activate automatic downshifting.  I would be anticipating the situation and already be manually downshifting.   This truck replaced a 2004.5 LLY diesel with the Allison 5-speed.  Putting it in T/H made noticeable differences (when the torque converter locked, upshift points, downshift behavior).  On this 2024 gasser with the 10L1000 I haven't been able to detect much, if any, difference.  Ok, I can never tell now when the torque converter locks up.  But I also don't notice differences in shifting.  For downhills, I've probably already manually downshifted by then anyway.  Since it's also more awkward (than the 2004.5) to engage/disengage I don't even bother.  Or maybe it doesn't really matter with just a 3k lb. camper in the bed?   Thanks also for the list of reasons the charging system might select various voltages.  However, what I am seeing doesn't fall into any of those categories.  It very definitely, and very consistently, rises after coasting/braking.  Maybe not immediately, but not very long after coasting/braking.  Very consistently drops voltage when no longer coasting/braking.  It might also be interacting with the camper battery charging (I might disconnect the camper and see if it changes the charging behavior).  I also need to recheck turning on headlights for when I want to force it to charge the camper.   Another JR, in June I converted the camper to LiFePO4.  Since it's not a good idea to try to charge lithiums directly using truck, I installed a Victron Orion XS DC-DC charger (which BTW is AMAZING!!).  Being cheap, I only had to buy that one item (besides the battery, of course) to do the conversion.  The camper OEM 120v battery charger (only 19 years old and works perfectly) and the truck feed the input to the DC-DC charger (not at the same time).  But I didn't want the camper charger feeding back to the truck so I kept the old separator.  I considered replacing the separator with a 30amp diode but that means more work and might add another 1/2 volt drop.  One thing that surprised me was the voltage drop over the long 10awg wire run, so I can only charge smoothly at 8 amps (because the DC-DC charger is completely configurable).  Another reason I don't want an added voltage drop with the diode.  I might also be a little lazy but all this work is being done under the sink with a small cabinet opening.    

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