Hard Shift?
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Hard Shift?
Hey everyone i am new to corvettes, i picked up a 1978 25th anniversary about a week ago and she ran great. yesterday i drove around quite a bit and it worked awesome but today i got in started it up and put it in drive and when i would apply gas it would bog down and then go but it dosnt want to change gears unless i take my foot off the gas to let it shift. i can floor it and the rpms will go high but it wont change until i take my foot off the gas then it will go up a gear. any ideas? 
Thanks!
Thanks!
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Joined: Sep 2013
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From: Pflugerville Texas
Sounds like a vacuum issue, you need to check the vacuum modulator. Check to make sure the vacuum line is not cracked and that it is dry. If the vacuum line is wet the modulator needs to be replaced.
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Awesome thanks for the photo i had no idea that was there. i will put it up on a lift and take a look. the reason i asked about the exhaust is because i want to replace the current fake dual with side mounted exhaust.
Race Director
Joined: Mar 2003
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From: Eustis ( Area 51 Bat Cave ) Fl
Exhaust doesnt normally have effects on an automatic shifting that I know of,
On my 69 it has a th400 tranny my vacuum line the metal part got mashed almost flat and caused a problem much like yours....
On my 69 it has a th400 tranny my vacuum line the metal part got mashed almost flat and caused a problem much like yours....
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Joined: Sep 2013
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From: Pflugerville Texas
But really I am pretty sure you have a modulator issue.
If you chase the metal line up to the engine you will find it also has a small rubber hose connected the the intake manifold, make sure to check it for cracks also.
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haha that just may be my problem :P i was looking at some of the rubber hoses today and they are not in good shape. this corvette sat for 9 years then the guy i bought it from had it running for about 6 months.
Burning Brakes
Joined: Aug 2011
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From: Redding California
with The13Bats and Tejasak. Welcome to the world of C3's. You may not be handy with a wrench at the moment, but if you plan on driving your 38 year old Vette for an extended period of time you're going to get pretty familiar with the mechanics of it
Keep us posted and good luck.
Team Owner
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From: Ontario
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Awesome! you have all been a ton of help. i thought the repair was gonna cost an arm and a leg but its only like $12! the soonest i can get it up on a lift will be friday or saturday but i will keep you all posted. just looking at the modulator it just pushes into the transmission? Any ideas of a good place to get the side mounted exhaust?
Team Owner
Joined: Aug 1999
Posts: 30,995
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From: Ontario
Awesome! you have all been a ton of help. i thought the repair was gonna cost an arm and a leg but its only like $12! the soonest i can get it up on a lift will be friday or saturday but i will keep you all posted. just looking at the modulator it just pushes into the transmission? Any ideas of a good place to get the side mounted exhaust?
When I removed mine it appeared that the internal diaphragm had developed a pinhole leak and some transmission fluid had found its way in the vacuum tube. This caused some erratic shifting.
Race Director
Joined: Mar 2003
Posts: 11,608
Likes: 780
From: Eustis ( Area 51 Bat Cave ) Fl
with The13Bats and Tejasak. Welcome to the world of C3's. You may not be handy with a wrench at the moment, but if you plan on driving your 38 year old Vette for an extended period of time you're going to get pretty familiar with the mechanics of it Keep us posted and good luck.I couldnt afford a vette if I didnt do most of the work on it,
Get a good generic auto repair manual, not too new, something that covers the 70-80's not modern computer controlled everything,
Then if you really get into it go for a 78 assembly manual, they are nice to have especially if you are a bit new to vettes wrenching or both,
Team Owner
Joined: Aug 1999
Posts: 30,995
Likes: 98
From: Ontario
I couldnt afford a vette if I didnt do most of the work on it,
Get a good generic auto repair manual, not too new, something that covers the 70-80's not modern computer controlled everything,
Then if you really get into it go for a 78 assembly manual, they are nice to have especially if you are a bit new to vettes wrenching or both,
