Automatic transmission repair

An automatic does its work without asking you to do anything, so when it goes wrong the first sign is usually a feeling: a slip, a thud, a shudder or a delay. The shop sums up its approach in one line: "We will diagnose the situation to determine the kind of service you need." That is how every automatic that comes through the door starts.

How an automatic decides when to shift

Inside the case, fluid pressure applies clutch packs and bands that lock different parts of a planetary gear set. Changing which parts are locked changes the gear ratio. A valve body full of small passages and solenoids routes the fluid, and the vehicle's computer reads speed, throttle and engine load to tell the solenoids what to do. A torque converter sits between the engine and the gears and lets the engine keep turning while the vehicle sits still at a light.

That is a lot of moving parts sharing one pool of fluid, which is why fluid condition matters so much and why a small fault in one area can look like a big one. The guide to how an automatic transmission works goes further.

Problems that point to the automatic

Several of these have causes outside the transmission, such as a sensor, a wiring fault or an engine problem that the computer reacts to. Another reason to diagnose before repairing.

• The engine revs but the vehicle is slow to respond, covered under transmission slipping
• A pause before the vehicle moves after you select Drive or Reverse, see delayed engagement
• A shake or buzz at steady speeds, often called torque converter shudder
• The vehicle stuck in one gear, known as limp mode
• Fluid on the ground, a burning smell or a rising temperature reading

What the shop looks at first

The shop asks what the vehicle is doing and when, then looks at the basics: fluid level, fluid condition and any leaks. It reads stored codes where there are any and drives the vehicle to see the problem for itself. From there the answer might be a repair outside the case, a repair inside it, or a rebuild. When the work is a full overhaul, the rebuilds and overhauls page explains it.

Heat, towing and mountain driving

Heat is the enemy of automatic transmission fluid. Reno's normal July high is about 94 degrees Fahrenheit according to NOAA's 1991 to 2020 normals, and towing a trailer or climbing toward Tahoe or Mount Rose adds load on top of that. Drivers who tow or haul regularly should read the towing, summer heat and your transmission guide.

Which vehicles and what to ask when you call

The shop works on automatics in cars, trucks, SUVs, RVs and 4x4s, foreign and domestic. Have the year, make, model and engine ready, plus what the vehicle is doing. Ask about cost, timing and warranty coverage; the shop will answer for your vehicle after it has looked.