Jump to content

Transmission Vacuum Modulator


Recommended Posts

Anyone know a good source for a new transmission vacuum modulator for my '65.  Everything I see online does not look like what I currently have.  I have the original BR transmission. 

 

Thanks

IMG_1635.JPG

IMG_1638.JPG

Link to post
Share on other sites

Your transmission is basically a GM Turbo Hydramatic 400 and I would think the vacuum modulators should be the same for all TH400's.  

 

Link to post
Share on other sites

You're correct that the "new" vacuum modulators don't look the same--they're physically smaller than the older units.  Rest assured they all function the same AND have an adjustment screw inside the vacuum line port for changing the shift points.  Your local Napa will have the best brick&mortar price, but you can see the full range available new today on Rock Auto.com.  Their price will be more expensive than Napa's after factoring their sky-high shipping charges.

Link to post
Share on other sites

Hans3,

 

    Your original modulator DOES have an adjustment on it.   DON'T DRIVE YOURSELF CRAZY TRYING TO FIND AN ORIGINAL. The smaller one functions just as well or maybe even better than the original.

 

Tom T.

Link to post
Share on other sites

Modulators have a diaphragm inside that occasionally fails, and should be viewed as consumables like tires, batteries, and hoses. Look for an original only if it's for show, otherwise take Hans3 and telriv's advice and get the new one.

 

Be sure to verify the adjustment. It affects the shift points as well as the internal pressures. I don't have one in front of me, but I believe the shop manual will tell you when it should shift.

Link to post
Share on other sites

With very light throttle the trans. will shift from 1st. to 2nd.  at around 5-8MPH.  2nd. to 3rd. with light throttle should be at around 15-18MPH.  Turn the internal screw out for sooner shifts 1/2 turn at a time. AND in for later shifts  1/2-1 turn at a time.

IF it has 3.42 gears the shifts will be slightly/little sooner.

  • Like 1
Link to post
Share on other sites

Delayed upshifts on a Turbo 400 is your queue to inspect the vacuum plumbing to the modulator.  I've never actually had a modulator fail, but have had several instances where the vacuum hose at one end or the other of the steel line has disintegrated.

Edited by EmTee (see edit history)
Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...