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1991 Chevy Truck Transmission has overdrive & shifting

Tiny
SFLYBOY
  • MEMBER
  • 1991 CHEVROLET TRUCK
  • V8
  • 4WD
  • AUTOMATIC
  • 147,769 MILES
Sometimes when the truck is shifted into overdrive the transmission won't shift out of drive into overdrive instead the RPMs climb to redline. Other times it will shift back and forth between drive and overdrive very quickly. Also when it shifts between any gear it sometimes shifts hard with a load thud and you can really feel it. This all started all of a sudden a week ago.

The truck is a 1991 Chevy 1/2 ton extended cab truck 4x4 with a 5.7L V8 EFI engine. I do not know what the automatic transmission is or were to look but I am pretty sure it's the factory original.

Any help would be greatly appreciated.

Thanks
Shane
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Sunday, September 27th, 2009 AT 12:02 PM

7 Replies

Tiny
DOCFIXIT
  • MECHANIC
  • 18,828 POSTS
Hi
Maybe faulty shift solenoid or TCC. Find ALDL underdash see figure


https://www.2carpros.com/forum/automotive_pictures/198357_Graphic_150.jpg


Jumper between term. A&B paper clip will do turn key on DO NOT start. MIL will flash like flash, flash, pause flash that's 21. see what codes are present and post.
Thanks for donate
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Monday, September 28th, 2009 AT 9:54 AM
Tiny
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  • MEMBER
  • 5 POSTS
The only code I got was 12 and 82.
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Monday, September 28th, 2009 AT 7:58 PM
Tiny
DOCFIXIT
  • MECHANIC
  • 18,828 POSTS
12 means no engine code 82 means shift solenoid "A" faulty. Need to drop pan to get at solenoid on valve body


https://www.2carpros.com/forum/automotive_pictures/198357_Grafic_3_43.jpg

. ground terminal "B" at ALDL solenoid should click if no replace.


https://www.2carpros.com/forum/automotive_pictures/198357_Graphic_158.jpg

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Tuesday, September 29th, 2009 AT 9:24 AM
Tiny
SFLYBOY
  • MEMBER
  • 5 POSTS
I replaced the shift solenoid "A" and the trany shifts better then it has in a long time.

Thank You!
Shane
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Wednesday, October 21st, 2009 AT 5:01 PM
Tiny
DOCFIXIT
  • MECHANIC
  • 18,828 POSTS
Glad to hear that Thanks for letting me know. So often I never know if been helpful.
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Thursday, October 22nd, 2009 AT 9:39 AM
Tiny
SEC_FIDDLE
  • MEMBER
  • 3 POSTS
Thanks ya much!
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Sunday, June 5th, 2016 AT 9:50 AM
Tiny
SEC_FIDDLE
  • MEMBER
  • 3 POSTS
Transmission shifts late.
At about 30-40-&50-55.
91 Silverado 5.7.
Is shift solenoid possibly going bad?
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Sunday, June 5th, 2016 AT 9:56 AM

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