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December 5, 2007
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about 4 months ago
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There are more airplanes at the bottom of the ocean than there are submarines at the top of the sky.
News - Enginursday: This is why …
about a year ago
If that diaphragm was ruptured, you would get no fluid transfer from the transmission to the intake manifold, because when the pedal is mashed, there is no appreciable intake manifold vacuum, therefore no flow.
The flow (smoke, etc) will happen when you let off the pedal and generate maximum manifold vacuum, eg. high rpm’s, low engine load, deceleration.
The vacuum modulator decreases transmission fluid line pressure to the shift valves in response to manifold vacuum. More throttle = Less manifold vacuum = higher engine load = less transmission fluid line pressure = need to have higher rpm’s in the transmission, more accurately at the governor, to generate the required line pressure to activate the shift valve for the next gear. And it’s essentially out of the picture once you get past about ½ throttle in most situations.
When you “mash the pedal to the floor”, you are activating the ‘detent lever’ which is another valve in the transmission which basically dumps all shifting line pressure until the governor (which is driven by rpm) is able to overcome that and allow an upshift.
So, in short, if you’ve got a blown vacuum modulator diaphragm, the only way to keep it from smoking, is to run the engine wide open all the time (eg. no manifold vacuum) or not run it at all (eg. again, no manifold vacuum).
Need to split these gizmo’s into two categories…
vacuum modulator = adjusting normal up and down shifts at normal throttle positions (and causes smoke when it rips)
detent valve = the downshift when you mash or the upshift when you un-mash.
Not a downshift mechanism. That’s the vacuum modulator, which modifies the shift points according to engine load (eg. manifold vacuum). The downshift is the rod extending from the back of the carb off the throttle linkage down to the transmission.
It’s a relatively common failure point in GM’s, Fords, Dodge’s, basically anything with an automatic transmission of that era that used a vacuum operated diaphragm to modify shift points.
about 2 years ago
Which “there” are you using in that sentence?
“there”, “their”, or “they’re”?
My reply depends on that answer…
“40K/CH Memory Depth”
News - September Caption Contest
about 2 years ago
How ‘bout that… It’s almost 3:00…
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