Transmission shudders, slips or shifts hard

With about 15,000 complaints across the vehicles covered here, the wording splits several ways. Four in ten mention slipping or engine revs, three in ten a hesitation or delay, about a quarter a shudder or vibration, and one in seven a clunk or bang. The median mileage owners give is about 48,000. One car stands out: the 2014 Ford Focus has more reports on this sheet than any other vehicle year, followed by the 2018 Ford F-150 and the 2014 Jeep Cherokee.

Firestone's list of transmission warning signs reads like a summary of these complaints: gears that won't shift or struggle to, slipping and over-revving when the car should be pulling, shaking or jolting during shifts, grinding and surges of power between gears, a burning smell or red fluid on the ground. Its first suspect for poor shifting is low or contaminated fluid. It also notes the check engine light can pick up transmission problems before you feel them.

Software plays a part too. One report in ten mentions a software update or reflash, and recalls in the data show why. Mitsubishi's 16V-563 reprogrammed the CVT control unit on some 2015 and 2016 Outlander Sport, Outlander and Lancer models because the transmission could hesitate during acceleration. Subaru's 21V-955 and 22V-485 reprogrammed the transmission control unit on some Ascent, Legacy and Outback models after a programming error could let the drive chain slip.

Expect a scan for stored codes and a check of the fluid level and condition, the two places Firestone's list points first. Ask whether a software update or a service bulletin applies before anything is taken apart. NHTSA posts the bulletins manufacturers file with it, searchable by year, make and model.

The car generally still drives, but don't wait long. If it slips so the engine revs without the car moving, or bangs into gear hard enough to lurch the car, treat it as urgent, since either one can catch you out in traffic. Firestone warns that ignoring the signs can end in a failed transmission, and if a transmission temperature light comes on, its advice is to stop and let it cool.

Tell the mechanic when it happens (cold or warm, from a stop or at cruising speed, up-shifts or down-shifts) and how often. A note of dates and mileage helps. Check NHTSA's recall lookup. And report it while the powertrain warranty still applies, because the FTC says a defect reported during the warranty period must be fixed even if the warranty expires before the repair.