Vehicles that have been modified are going to make some interesting noises versus unmodified rides. Some of these noises can be a sign of trouble, while others are just a part of what you deal with when you drive a custom vehicle. Gear rollover is something that might pop up if you install an aftermarket manual transmission, and it’s not as serious as it sounds.

There’s a lot of work that goes into bolting a new aftermarket manual transmission into your vehicle. After you complete the installation, new noises might be heard coming from under the vehicle that might sound like big problems. Numerous things like a part of the driveline touching the transmission tunnel, unbalanced parts, the type of bushings used, or other items could be generating strange noises or vibrations.

Now, if you hear something that sounds like a box of rocks being vibrated while the vehicle is in neutral, or while you’re engaging the clutch, that’s what’s known as gear rollover. You can diagnose gear rollover by starting the vehicle while the transmission is in neutral and with the clutch pedal fully disengaged. You’ll want to bring the car past idle to 2,500-3,500 rpm, at this point the noise should disappear or become softer.

Gear rollover can be annoying, but it doesn’t damage the transmission, or mean the transmission is having a serious issue. The noise is created as the engine vibrates the transmission physically or through harmonics.

The experts at Silver Sport Transmissions (SST) add some additional details about gear rollover.

“All transmissions make noise while the engine is running, but only some are loud enough to be heard in the cabin of the vehicle. The vibrations of the engine cause the gears, synchronizers, and other parts of the transmission to rattle against each other. It creates a sound that most people describe as a box of rocks. If you were able to see it happening through the case, you’d see it’s not a violent clanging of gears; it’s more like change jingling in your pocket. This action does not harm the internals of your transmission in any way.”

SST also noted that other factors will increase the likelihood of gear clatter noises being audible inside the vehicle’s cabin. Transmissions with larger gears are going to make more noise than transmissions with smaller gears. That means that TREMEC Magnum and TR-4050 transmissions are more prone to gear rollover noises versus TREMEC TKX and T-5 transmissions. Vehicles that have low idle and aggressive cams can also create vibrations that will cause gear rollover noise.

According to SST, there are a couple of things you can do to easily reduce the impact of gear rollover noise.

“There are two ways to dampen the noise and they may eliminate the noise entirely from the cabin. First, you can use a thicker, approved fluid like TREMEC HP-MTF, and make sure you’re using the amount suggested. Second, you can add thermal/acoustic insulation between the transmission tunnel and the carpet. This won’t only cut down on the noise, but it will also help regulate the cabin temperature.”

Hopefully, this will ease your mind when a new transmission starts to make some strange sounds. Gear rollover noise isn’t anything serious to worry about and it can be reduced to nominal levels with a little bit of work.