Modulater valve
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The symptoms of a bad modulator are 1)won't upshift or late upshift more likely. 2)smoke out the exhaust followed by low fluid level.
Engine intake manifold vacuum is applied to one side of the modulator diaphragm. At idle, vacuum is high, and at cruise, vacuum rises a little. When you step on the gas, vacuum falls, allowing the modulator spring to push against valve body stuff. When you let off the gas, or the engine approaches 'easy work' at higher rpm, the vacuum rises a bit, so the diaphragm gets retracted, letting the valve body move towards 'upshift'. Additionally, the governor is cranking along, increasing its 'force' proportional to the increase in speed, so the modulator has additional forces 'pulling' for the transmission to "upshift as soon as you can, bud". This happens in each gear position, except R, I think.
Generally, once set properly, you never have to mess with a modulator. They work or they don't. If you aren't getting upshifts, check the vacuum connections at the manifold & modulator.
tom
The symptoms of a bad modulator are 1)won't upshift or late upshift more likely. 2)smoke out the exhaust followed by low fluid level.
Engine intake manifold vacuum is applied to one side of the modulator diaphragm. At idle, vacuum is high, and at cruise, vacuum rises a little. When you step on the gas, vacuum falls, allowing the modulator spring to push against valve body stuff. When you let off the gas, or the engine approaches 'easy work' at higher rpm, the vacuum rises a bit, so the diaphragm gets retracted, letting the valve body move towards 'upshift'. Additionally, the governor is cranking along, increasing its 'force' proportional to the increase in speed, so the modulator has additional forces 'pulling' for the transmission to "upshift as soon as you can, bud". This happens in each gear position, except R, I think.
Generally, once set properly, you never have to mess with a modulator. They work or they don't. If you aren't getting upshifts, check the vacuum connections at the manifold & modulator.
tom
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