CT5635 - A new made in USA vacuum modulator for the Cast Iron Powerglide transmission for the years 1958 1959 1962 1961 & 1962. All modulators will eventually go bad. And when this happens tranny fluid gets sucked into your engine's intake resulting in exhaust smoke and other bad things. It is a good idea to replace your modulator on a regular basis. If you can't remember when you last changed your modulator, then it is time to replace it. It's an easy job and it will save you lots of trouble down the road. Fiber gasket included. Note: this modulator does not work on aluminum powerglide transmissions.