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Discussion Starter #1
I have an automatic coupe , and the past two days it won't shift gears right. It revs up high and then sits at the level of Rpm and then shift hard into the next gear. Any ideas of why this is very appreciated, thanks!
 

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These automatics are vacuum modulated. Check the vacuum line. It is a hard line from the transmission up to the back of the manifold, then a short rubber piece to connect it to the manifold. Check that rubber piece.

My '67 drove great forever and then started shifting late and hard suddenly. I topped off the fluid to no change, then I discovered that my vacuum line had a nice 3" split in it. Replaced it and all was well.

And the transmission lived happily ever after.

-Matt
 

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These automatics are vacuum modulated. Check the vacuum line. It is a hard line from the transmission up to the back of the manifold, then a short rubber piece to connect it to the manifold. Check that rubber piece.

My '67 drove great forever and then started shifting late and hard suddenly. I topped off the fluid to no change, then I discovered that my vacuum line had a nice 3" split in it. Replaced it and all was well.

And the transmission lived happily ever after.

-Matt
+1.....I would guess either a vacuum leak or low fluid level..Most likely it's not getting vacuum..
 

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Discussion Starter #4
@lemonshindig thanks a lot! but im having trouble finding the line? i dont see a rubbery piece that connects to the manifold, does the car need to be jacked up to see it?

sorry, this is my first car so i'm just starting to learn things.
 

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Take off the air cleaner and look at the back of the manifold. The line will come off a fitting and run down the back of the engine toward the transmission, I believe on the passenger side.

Good luck,
MrFreeze
 

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Discussion Starter #6
Take off the air cleaner and look at the back of the manifold. The line will come off a fitting and run down the back of the engine toward the transmission, I believe on the passenger side.

Good luck,
MrFreeze
thanks! there is a line there, but its metal and screws in. but it heads down towards the trani so i guess ill jack it up?
 

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Discussion Starter #7
I FOUND IT, but its like a rubber piece that goes over the metal, so where do i buy that rubber piece? or do i need a new metal line?
 

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pull it off take it to the auto parts store and ask for half a foot of whatever line it is (show it to them) bring it home and put it back on. see if it fixes the problem
 

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Well, visually inspect the rubber line. If the hose is still flexible, there are no cracks, and it fits both metal pieces snugly, then look elsewhere.

If the hose is hard, or cracked, or fits one of the lines loosely, replace it. As stated above, the auto parts stores sell rubber hose by the foot. They will cut a piece to match for you.

-Matt
 

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Discussion Starter #10
well it seems like the problem is back! but its not the rubber hose piece....what else could it be?
 

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The modulator itself could be bad. Are you talking about the 1-2 shift? If you pulled the hose off the modulator and any fluid came out, it is bad for sure.
 

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Thanks guys! My 67 was shifting hard and late, not acting like it was supposed to, I checked the vacuum line going to the modulator, it was completely off, reconnected it. She now shifts perfect. Wow what a relief. I was thinking "rebuild" ugh! Had me really worried.

1967 GTA Convertible
351 Cleveland, C4
Positraction 9 inch rear end.
 

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+1 on the modulator.

If it's bad you'll be sucking fluid, any sign of fluid in your line?

Do you have power brakes?

How's the hard line coming off the rubber hose look, pinched anywhere?

Check your vacuum with a vacuum gauge where your line is hooked up, you said it's directly to the manifold iirc, check your vacuum there.

Also check your intermediate band to make sure it doesn't need adjusting.

And your fluid level while the car is hot, on a level surface, running in park.

Eric


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I am assuming that you have a C4. Which shift points are effected? Are you still getting both shifts? What speed are they occurring? Checking the items that 67HardtopV8 gave you should get you through the most common issues.

The only thing I would add is to check the kick down linkage and valve to make sure that it is free. It attaches by a cable from the accelerator linkage on the engine side of the firewall to a small arm on the left side of the transmission. Under hard acceleration it will pull the cable forward and move a valve that will keep the car in gear longer before allowing it to shift. Just a thought.

Kevin
 
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