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Old 09-22-2014, 11:11 AM   #1
vjjack04
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hard 1-2 shift fix

I have a 2006 GMC and just today the transmisison started shifting really hard from 1st to 2nd gear. Check engine light is also on. The truck is a 2006 GMC Sierra 4 wheel drive with a 5.3 liter V8. Any ideas?
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Old 09-22-2014, 09:22 PM   #2
Old Money
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Re: hard 1-2 shift fix

yes i had that same problem in 05 gmc k1500. valve body in transmisson is culprit. take it to a transmission shop. google problem. it cost me 300 dollars, fluid, filter,and parts and labor. old money.
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Old 09-25-2014, 10:36 PM   #3
clinebarger
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Re: hard 1-2 shift fix

What Codes are set?
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Old 09-26-2014, 08:43 AM   #4
Old Money
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Re: hard 1-2 shift fix

1870 i think, trans.componet slipping.
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Old 09-26-2014, 08:35 PM   #5
clinebarger
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Re: hard 1-2 shift fix

Quote:
Originally Posted by Old Money View Post
1870 i think, trans.componet slipping.
The Infamous P1870, That will cause a harsh 1-2 shift.

The most common cause is the Isolation-PWM Converter Valve has worn the Bore that it rides in.

The Actuator Feed Limit Bore wears as well, The controls pressure to the ISO-PWM Conv. Valve.

Sonnax makes fixes for both, Requires the Valve Body to be reamed for oversized valves. The Tool kit for both bores are around $800, So its not something a DIY'er wants to pay entry price for.

VBX is owned by Sonnax & will have all the updates, http://valvebodyxpress.com/prodView.php?theId=65
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