kdml Posted July 18, 2020 Share Posted July 18, 2020 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 Link to comment Share on other sites More sharing options...
RivNut Posted July 18, 2020 Share Posted July 18, 2020 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 comment Share on other sites More sharing options...
Hans3 Posted July 18, 2020 Share Posted July 18, 2020 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 comment Share on other sites More sharing options...
telriv Posted July 18, 2020 Share Posted July 18, 2020 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 comment Share on other sites More sharing options...
kdml Posted July 18, 2020 Author Share Posted July 18, 2020 Thanks all i figured the replacements would work. Just thought it best to confirm first. Link to comment Share on other sites More sharing options...
Bloo Posted July 18, 2020 Share Posted July 18, 2020 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 comment Share on other sites More sharing options...
telriv Posted July 18, 2020 Share Posted July 18, 2020 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. 1 Link to comment Share on other sites More sharing options...
EmTee Posted July 19, 2020 Share Posted July 19, 2020 (edited) 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 July 19, 2020 by EmTee (see edit history) Link to comment Share on other sites More sharing options...
Rafz66riv Posted January 8 Share Posted January 8 On 7/19/2020 at 6:07 AM, EmTee said: 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. What size is the hose going to the modulator? Mines keeps coming loose and won’t stay connect to the modulator on my 66 riv Link to comment Share on other sites More sharing options...
EmTee Posted January 8 Share Posted January 8 (edited) I believe the hose is 1/4-inch. Yours sounds like it has disintegrated due to age and exposure to oil. 90° formed hoses are available for a better fit. My '67 has a metal line with the bend in it and only uses a short, straight piece of hose to join the metal line to the modulator nipple. Example: https://www.monstertransmission.com/TH400-3L80-Hose-Modulator-Elbow-51-Up-MERCH_p_17292.html Edited January 8 by EmTee (see edit history) 1 Link to comment Share on other sites More sharing options...
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