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I have a 1978 chevy k20 4x4 truck. Lately my transmission will not shift to third gear, and if it does, it shift back down to second gear.

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On the back right side of the tranny you will find the modulator valve with a vaccum line. First check the the line is ok, if so, replace the valve. Note; there is an adjusting screw inside the vaccum hose fitting to change the shift modes. Don't mess with it unless necessary! Frankster016

Posted on Dec 02, 2008

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The turbo 400 is one of the bestest transmissions ever made...check vacuum modulator for clogged ripped or pinched hose (side trans near back bulbous with vacuum line to it )...advise me if that does not correct it

Posted on Dec 02, 2008

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SOURCE: 1978 chevy k20 4x4 truck

try checking your vacume lines..

Posted on Dec 02, 2008

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I have a 1978, 2wd, old chevy pickup with a 305 engine in it. It has a automatic transmission. It recently has not been wanting to shift into reverse. Any help?

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When it shift from third gear to second gear it makes an abrupt shift. This problem is only from third to second gear, the other gears shift nice and quiet. The transmission is new only 3 months old.

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1978 chevy k20 4x4 truck

try checking your vacume lines..

Dec 02, 2008 | 1983 Chevrolet C2500

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