When very low gearing is used behind an automatic transmission, downhill compression braking can be substantial and highly beneficial, allowing you to keep your foot off the brakes and reduce heating them up. One word of caution is in order when it comes to the use of low-low doublers mated to a manual transmission. If you have a 10:1 low-low-range, you’re geared four to five times lower than a stock T-case. Should you be coming down a hill in deep low-range and gain too much speed with the clutch pushed in, it’s possible to quickly exceed the maximum rpm rating of the clutch disc. In such a case, you can literally spin one apart and destroy it under these circumstances.