Question on vacuum modulator
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Elder User
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Question on vacuum modulator
My transmission was rebuilt completely in January and by a very good mechanic. So this morning I noticed the transmission shifting weird when warmed up. When going from 1-2, it jerks back and forth like it doesnt know which gear to go in, then seems to jump to third. when I manually shift the truck, all is just fine. I noticed the idle to be a little higher and rough as well (vacuum leak?). When I squeezed the vacuum line going down to the modulator, the idle smoothed out.
Back in January, the mechanic did not replace the modulator valve - I had put one on a few years ago and told him not to do it.
Can the modulator be the cause of this?
Back in January, the mechanic did not replace the modulator valve - I had put one on a few years ago and told him not to do it.
Can the modulator be the cause of this?
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Elder User
Joined: May 2008
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Found it. It was the small piece of vacuum line that connects the hard line to the modulator nipple. The intake manifold leaks so bad that it had softened / swelled the hose.
So another question - this has been this way (I think) since I got it rebuilt and am just figuring this out. My truck actually misses second gear. It goes from 1 to 3. If I manual shift, from 1-2-3, all gears are just fine.
Would any adjustment in the modulator valve allow for this, or is this more of a transmission band adjustment?
So another question - this has been this way (I think) since I got it rebuilt and am just figuring this out. My truck actually misses second gear. It goes from 1 to 3. If I manual shift, from 1-2-3, all gears are just fine.
Would any adjustment in the modulator valve allow for this, or is this more of a transmission band adjustment?
New User
Joined: Oct 2014
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if you have a tach keep an eye on it to see if you can see when the trans shift. on my 71 from first to second is a hard felt shift which is a bad thing that needs adjusting but from second to third is smooth and can hardly be felt if at all but I can see when it shifts on the tach .
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