Question about trans vac modulator - The 1947 - Present Chevrolet & GMC Truck Message Board Network

NINERS1 · 05-10-2011, 06:10 PM

Hey guys, does anyone know if a bad vacume mod on a th 400 trans would cause my trans to only have park and 1st? no matter where i shift to it's 1st. already unhooked the linkage and shifted it at the trans output shaft to eliminate column and linkage, same thing no reverse or neutral. and checked the vac lines from the mod to the intake seem to be fine. could it be the modulator causing this?

sean1969c10 · 05-10-2011, 08:12 PM

You will usually have 1st and reverse, the trans just won't shift without the modulator working.

BIGKEV · 05-10-2011, 10:53 PM

Sound like you may have a valve hanging up in the valve body. Does it feel like it's engaging reverse and drive at the same time by chance?

NINERS1 · 05-11-2011, 07:37 AM

not so much reverse and drive but does seem like its in neutral till you give it some gas then drive! damn just my luck, i know nothing about transmissions. expensive to fix? thanks for the help guys. i do appreciate it.

05-10-2011, 06:10 PM	#1
NINERS1 Registered User Join Date: Feb 2006 Location: weatherford ok. Posts: 255	Question about trans vac modulator Hey guys, does anyone know if a bad vacume mod on a th 400 trans would cause my trans to only have park and 1st? no matter where i shift to it's 1st. already unhooked the linkage and shifted it at the trans output shaft to eliminate column and linkage, same thing no reverse or neutral. and checked the vac lines from the mod to the intake seem to be fine. could it be the modulator causing this? __________________ 71 chevy cheyenne lwb http://s321.photobucket.com/albums/n..._tab_my_albums Democracy is two wolves and a lamb voting on what to have for lunch. Liberty is a well-armed lamb contesting the vote!

05-10-2011, 08:12 PM	#2
sean1969c10 Registered User Join Date: Mar 2008 Location: Powhatan, Va. Posts: 376	Re: Question about trans vac modulator You will usually have 1st and reverse, the trans just won't shift without the modulator working.

05-10-2011, 10:53 PM	#3
BIGKEV Registered User Join Date: Jan 2011 Location: Prescott AZ Posts: 112	Re: Question about trans vac modulator Sound like you may have a valve hanging up in the valve body. Does it feel like it's engaging reverse and drive at the same time by chance?

05-11-2011, 07:37 AM	#4
NINERS1 Registered User Join Date: Feb 2006 Location: weatherford ok. Posts: 255	Re: Question about trans vac modulator not so much reverse and drive but does seem like its in neutral till you give it some gas then drive! damn just my luck, i know nothing about transmissions. expensive to fix? thanks for the help guys. i do appreciate it. __________________ 71 chevy cheyenne lwb http://s321.photobucket.com/albums/n..._tab_my_albums Democracy is two wolves and a lamb voting on what to have for lunch. Liberty is a well-armed lamb contesting the vote!

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