In other words, a vacuum modulator "modulates" the transmission's shift points to engine load rather than just plain vehicle speed. See All 8 Photos A vacuum modulator references engine vacuum to ...

Here, Darrell Young demonstrates modulator adjustment on a Turbo 350 with the vacuum hose removed. T uning an automatic transmission is perhaps the most gratifying, low-cost modification you can ...

Air leaking into your car—not out of it—can be a problem. Popular Mechanics’s automotive experts outline the tools and techniques proven to smoke out even the toughest to find vacuum leaks.

Having a manual transmission comes with extra maintenance, and if yours has a stiff gear shift, it's a cause for concern. Here are the most likely culprits.