Transmission shifting hard all of a sudden - Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum



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Go Back   Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum > 2002 - 2009 TrailBlazer/Envoy Tech > 02-09 Vortec 4.2L I-6 Engine and Drivetrain > OEM Issues

OEM Issues Original Equipment Repairs and/or Problems

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  #1  
Old 07-08-2019, 10:21 AM
lukeclement lukeclement is offline
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Join Date: Mar 2019
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Transmission shifting hard all of a sudden

Hey guys, was camping over 4th of July weekend.
2003 Trailblazer LTZ 4.2l 4x4
On the way back into town, only about 20 miles from home, I noticed that while in overdrive, my RPM kept bouncing between 2000-2200 while cruising at 55. So I kicked it into third and it was fine. Then, coming back into town, I hit a stop light, when I slowed down, I did downshift to second, and it shifted really fast and hard. Then at the light put it back in third once stopped. When I accelerated off the light, the 1-2 shift and the 2-3 shift were extremely hard and fast, like a big jolt. Kept doing it on the way home.

Any ideas?
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  #2  
Old 07-09-2019, 10:03 PM
miketexas miketexas is offline
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2003 Chevy TrailBlazer LS
Black 4.2L I6 2WD
Join Date: Feb 2018
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Quote:
Originally Posted by lukeclement View Post
Hey guys, was camping over 4th of July weekend.
2003 Trailblazer LTZ 4.2l 4x4
On the way back into town, only about 20 miles from home, I noticed that while in overdrive, my RPM kept bouncing between 2000-2200 while cruising at 55. So I kicked it into third and it was fine. Then, coming back into town, I hit a stop light, when I slowed down, I did downshift to second, and it shifted really fast and hard. Then at the light put it back in third once stopped. When I accelerated off the light, the 1-2 shift and the 2-3 shift were extremely hard and fast, like a big jolt. Kept doing it on the way home.

Any ideas?
Codes?
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  #3  
Old 07-10-2019, 11:17 AM
lukeclement lukeclement is offline
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Quote:
Originally Posted by miketexas View Post
Codes?
No codes, hooked up hptuners to it and found nothing. It's not doing it anymore, thinking maybe I heated up the clutch packs and it shifted hard to minimize slipping? Lots of steep hills with fast moving traffic and loaded fairly heavily. Maybe just a self protection mode? Dont know if anything like that exists, but it's back to normal now.
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  #4  
Old 07-17-2019, 07:09 PM
gammarider gammarider is offline
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2003 GMC Envoy SLT
Carbon Black Metallic 4.2L I6 2WD
Join Date: Oct 2009
Location: SF Bay Area
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When was the last time you flushed and replaced the trans fluid?
I had a clunk going into 2nd which was fixed by this.
Also, was it very hot out when this happened?
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  #5  
Old 07-17-2019, 07:20 PM
miketexas miketexas is offline
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2003 Chevy TrailBlazer LS
Black 4.2L I6 2WD
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Originally Posted by gammarider View Post
When was the last time you flushed and replaced the trans fluid?
I had a clunk going into 2nd which was fixed by this.
Also, was it very hot out when this happened?
People never can seem to learn that changing the trans fluid doesn't fix anything.
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  #6  
Old 07-17-2019, 07:28 PM
gammarider gammarider is offline
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2003 GMC Envoy SLT
Carbon Black Metallic 4.2L I6 2WD
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Location: SF Bay Area
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Before and after results
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  #7  
Old 07-18-2019, 12:06 AM
Almad Almad is offline
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2008 Chevy TrailBlazer LS
White 4.2L I6 4X4
Join Date: Nov 2012
Location: Saudi Arabia
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Did you check speed sensor, as I have the same issue and local dealer says it's cos of speed sensor and throws code 716 & 717
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  #8  
Old 07-18-2019, 05:42 AM
miketexas miketexas is offline
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2003 Chevy TrailBlazer LS
Black 4.2L I6 2WD
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Originally Posted by gammarider View Post
Before and after results
Been working on this junk for 40 years. Changing the oil does nothing, but you keep wasting your money.
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  #9  
Old 07-18-2019, 07:14 AM
marineguy99 marineguy99 is offline
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2004 Chevy TrailBlazer LS EXT
Silverstone Metallic 4.2L I6 4X4
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Location: Texas
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If it were my truck and it's been say 40K since the last fluid change, I would do a pan drop and filter change. While I was in there, I would replace the A&B shift solenoids. Very easy to do and about $16 each on Amazon. Google 4l60e shift solenoid.

Some will say throwing parts at a vehicle is not the way to go. Agree, but for the price and the possible pay-off, this is what I would do.
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