Turbo 400 won’t shift into 3rd - The 1947 - Present Chevrolet & GMC Truck Message Board Network

**68350** · 07-22-2020, 09:09 AM

Im gonna try to dig into this today but figured I would get some ideas from other members here. I have a 68 impala I purchased a little while ago. It has a 327 with a turbo 400. The trans is supposedly only 5 years old approx with a few thousand miles. It will not shift into third unless you let off of the gas when youre driving. It will coast in 3rd that way, but as soon as you give it gas again it kicks it back into 2nd. Im gonna start with the obvious and make sure the vacuum line is in good shape running down to the module. If its not that, could it be the module or governor? Im hoping its something simple since it shifts into 3rd kind of

**Steeveedee** · 07-22-2020, 11:04 AM

First, make sure that the trans is full, and that the vacuum line is attached at both ends. Then pop the vacuum line off the modulator at the trans and see if fluid is leaking. It sounds like the modulator is bad, but could just be a vacuum hose.

**68350** · 07-22-2020, 03:20 PM

Thank you!

07-22-2020, 09:09 AM	#1
68350 Senior Member Join Date: Jan 2002 Location: Williston, ND Posts: 2,999	Turbo 400 won’t shift into 3rd Im gonna try to dig into this today but figured I would get some ideas from other members here. I have a 68 impala I purchased a little while ago. It has a 327 with a turbo 400. The trans is supposedly only 5 years old approx with a few thousand miles. It will not shift into third unless you let off of the gas when youre driving. It will coast in 3rd that way, but as soon as you give it gas again it kicks it back into 2nd. Im gonna start with the obvious and make sure the vacuum line is in good shape running down to the module. If its not that, could it be the module or governor? Im hoping its something simple since it shifts into 3rd kind of __________________ 68 Chevy CST/10, 50th Anniversary, 327/th400, 373 posi, buckets 68 GMC Shortbox Stepside, 402/th400, Tilt, Tach, Bucket Seats, 3.08 Positraction 69 Chevy Camaro SS, 383, 4 speed, positraction 70 Chevy El Camino SS396, Triple Black, 454/th400, Tach 70 Chevy Shortbox Stepside 4x4, 350/th350, Tilt, Tach, Cab Lights, Bumper Guards, Tow Hooks 70 Chevy 3/4 Longbox, 350/auto, 70k, SURVIVOR 71 Chevy Blazer, CST, 350/auto 71 GMC Sierra K2500, 454, 4 speed, 4.10 posi, 37s 71 Custom/30, Open Road, 350/th400, tilt 72 Chevy Shortbox Fleetside, 496 Stroker/th400, Tilt, Tach, Bucket Seats, 3.42 Posi 72 GMC Sierra Grande 2500. 427/th400, tilt, a/c, tool and stowage, buckets/console, 3.54 posi

07-22-2020, 11:04 AM	#2
Steeveedee Who Changed This? Join Date: Jan 2013 Location: Simi Valley, CA Posts: 10,081	Re: Turbo 400 won’t shift into 3rd First, make sure that the trans is full, and that the vacuum line is attached at both ends. Then pop the vacuum line off the modulator at the trans and see if fluid is leaking. It sounds like the modulator is bad, but could just be a vacuum hose. __________________ ~Steven '70 Chevy 3/4T Longhorn CST 402/400/3.56 Custom Camper Simi Valley, CA

07-22-2020, 03:20 PM	#3
68350 Senior Member Join Date: Jan 2002 Location: Williston, ND Posts: 2,999	Re: Turbo 400 won’t shift into 3rd Thank you! __________________ 68 Chevy CST/10, 50th Anniversary, 327/th400, 373 posi, buckets 68 GMC Shortbox Stepside, 402/th400, Tilt, Tach, Bucket Seats, 3.08 Positraction 69 Chevy Camaro SS, 383, 4 speed, positraction 70 Chevy El Camino SS396, Triple Black, 454/th400, Tach 70 Chevy Shortbox Stepside 4x4, 350/th350, Tilt, Tach, Cab Lights, Bumper Guards, Tow Hooks 70 Chevy 3/4 Longbox, 350/auto, 70k, SURVIVOR 71 Chevy Blazer, CST, 350/auto 71 GMC Sierra K2500, 454, 4 speed, 4.10 posi, 37s 71 Custom/30, Open Road, 350/th400, tilt 72 Chevy Shortbox Fleetside, 496 Stroker/th400, Tilt, Tach, Bucket Seats, 3.42 Posi 72 GMC Sierra Grande 2500. 427/th400, tilt, a/c, tool and stowage, buckets/console, 3.54 posi



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