1991 Chevy Truck Transmission has overdrive & shifting

1991 CHEVROLET TRUCK

147,769 MILES • V8 • 4WD • AUTOMATIC

SFLYBOY

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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

Sep 27, 2009 at 12:02 PM

DOCFIXIT

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Hi Maybe faulty shift solenoid or TCC. Find ALDL underdash see figure

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

Sep 28, 2009 at 9:54 AM

SFLYBOY

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The only code I got was 12 and 82.

Sep 28, 2009 at 7:58 PM

DOCFIXIT

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12 means no engine code 82 means shift solenoid "A" faulty. Need to drop pan to get at solenoid on valve body

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

Sep 29, 2009 at 9:24 AM

SFLYBOY

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I replaced the shift solenoid "A" and the trany shifts better then it has in a long time.

Thank You!
Shane

Oct 21, 2009 at 5:01 PM

DOCFIXIT

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Glad to hear that Thanks for letting me know.So often I never know if been helpful.

Oct 22, 2009 at 9:39 AM

SEC_FIDDLE

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Thanks ya much!!!

Jun 5, 2016 at 9:50 AM

SEC_FIDDLE

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3 POSTS

Transmission shifts late .
At about 30-40-&50-55.
91 Silverado 5.7.
Is shift solenoid possibly going bad????

Jun 5, 2016 at 9:56 AM