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Discussion Starter #1
Hello All: I got a problem with my 68 gto automatic HT400. All of a sudden it won't shift into second gear. The car was working great yesterday, and taking out for a ride after adjusting the timing the car won't shift into 2nd gear??
I was working on it for some time, and the temp got up to 210 degrees??? Would it being so hot not make it shift. Fluild level looks good, and very clean.
Bought car last Feb. It goes into reverse ok. Goes into drive ok. But won't shift into second gear. I've had it up over 2000rpms. Usually it shifts right away just taking off slow. I'm very confused.
Need some help here guy's.
Tks, Bob :)
 

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Uh oh
3000 rpm and 30 mph home eh ??

Sounds like a vacuum leak to the teansmission vacuum modulator..
there is a vacuum line off the front of the q jet .. passenger front..
2" of hose to a metal tube make sure these are snug ...
follow it down to the tranny ..... usually this is where the issue is

the 90 degree hose is usually soft or not snug on the tranny ... poor vacuum makes for late or no shifting ...

https://www.classictransmissionsolutions.com/th350-th400-vacuum-modulator-red-stripe-turbo-350-400-transmission-w-extra-hose-and-oring/?gclid=Cj0KCQjwtb_bBRCFARIsAO5fVvGREEWZxECGAWM-0G_fWHevYWfG6mEdQmTmRPQ5R5PHTSoa4qx0qCoaAvq9EALw_wcB


I am not a tranny guy ,,,, but my trucks run t 400 tranny ... and I have had this issue b4 also

Scott

if any tranny fluid is present IN the hose or on the nipple replace the vacuum modulator as it has failed ...

again I hope for an easy fix for you ,,,, is your carb a q jet ? is your modulator un like the picture and big n black ?
do you still have the steel tube down to the tranny ?
do you still have the clip on the bellhousing bolt for the tube to clip into for vibration wiggle that may have
yanked the hose off ?

thats all I got ... door bells ringin gotta go .............
 

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68 Posts
Discussion Starter #4
1968 transmission problem

Hello All: Well, you are all right. When I was doing the timing I disconnected the Vaccum line going down to the Transmission. All fixed... Dumb ass me...
LOL LOL Hahahah I was one scared GTO owner. New it had to be something simple.... Let this be an example to everyone. Check your work when your done.
Tks, Bob :)
 
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