Used Vacuum Modulator 1990–2019

The vacuum modulator was the original way older automatic transmissions read engine load and adjusted shift timing. Under light throttle and high vacuum it shifts early for fuel economy; under heavy load and low vacuum it delays the upshift so the engine can build power first. When the diaphragm ruptures, transmission fluid gets pulled into the intake manifold and the blue smoke tells the story. Redline has 12 used vacuum modulators from 8 makes, listed by 4 sellers. These are found on domestic automatics from the 1960s through the 1980s and are a known wear item on classic cars and trucks where keeping the original drivetrain intact matters. Harsh, early, or late shifts that don't respond normally to throttle, transmission fluid leaking into the vacuum line, and rough lurching gear changes are the signs. A ruptured diaphragm producing blue smoke from burning fluid is the unmistakable confirmation. Search by year, make, and model to find a modulator for your transmission. Common makes include Chevrolet, Honda, Infiniti, Mercedes Benz, Ford. Used OEM modulators are often the only option on older transmissions where new old stock has been exhausted.