1978 Chevy Truck what would cause the auto transmission fr

Tiny
DANCASSIDY
  • MEMBER
  • 1978 CHEVROLET TRUCK
  • V8
  • 2WD
  • AUTOMATIC
  • 89,000 MILES
This vehicle won't upshift out of first gear. Please let me know what can cause this. Thanks
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Tuesday, February 3rd, 2009 AT 10:53 PM

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Tiny
BOWTIE BABY
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  • 101 POSTS
If the modulator is bad or the vacuum line disconected it will not shift until about 25 or 30 mph. Check to make sure vacuum line is hooked up and you are getting vacuum to the modulator. If you are then you will have to replace the modulator, there fairly cheap(20-30dolars) and easy to change. It is located at the back of the tranny on the passenger side.
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Friday, February 6th, 2009 AT 2:40 AM
Tiny
DANCASSIDY
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Thanks, we checked the modulator and governor, changed the oil and filter too. Checked to be sure the detents matched on the tranny and the shifter. It refuses to upsift at all no matter what speed. Dan
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Friday, February 6th, 2009 AT 10:37 AM
Tiny
BOWTIE BABY
  • MEMBER
  • 101 POSTS
Well its hard to tell without driving the truck myself. You might want to take it down to a local tranny shop for a diagnostic, sometimes you can get them free, Aamco has free diagnostics sometimes. You might also want to check the shifter linkage to make sure it is going all the way into drive.
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Saturday, February 7th, 2009 AT 4:54 PM

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