Why Is My Transmission Slipping? Common Causes and Signs

Originally published on 03/21/2019
Updated on 04/04/2022

If your vehicle's transmission seems to be slipping, it can be a warning sign of failure to come.  Replacing a transmission in a car, truck, or SUV can vary significantly in cost but is among the most expensive and technically complex mechanical elements to repair or replace, sometimes costing thousands of dollars. 

Various factors can cause a transmission to slip. In some cases, a minor fix may solve the problem. A more significant fix will require more expert diagnostics, time, and money.

This article will discuss some of the most common causes of transmission slipping and some of the symptoms you should look for, and what could be causing them.

What Is a Transmission?

A vehicle transmission is a critical component that transfers and multiplies power from the engine to the wheels, allowing the vehicle to move. There are several types of vehicle transmissions, but all perform essentially the same function.

What Are the Signs of a Slipping Transmission?

Your transmission might be slipping if you notice any of these symptoms:

• You experience delays in engagement or acceleration when you step on the accelerator pedal  in your vehicle
• You notice that your vehicle seems to struggle to shift from one gear to the next
• You see a higher engine rev, RPMs, than normal on your dashboard tachometer when you're driving
• Your engine seems louder than normal
• You smell something burning while driving
• Your check engine light comes on and indicates an issue with the transmission
• Your fuel economy is suffering, and your vehicle is using an unusual amount of fuel during normal driving conditions

Don't ignore these signs! They could be letting you know that your transmission is slipping.

Now, let's check out some things that can cause automatic transmission slippage.

1. Transmission Fluid

Low transmission fluid is one of the most common reasons for a slipping transmission.

The most likely culprit is a problem in your system that's causing the transmission fluid to leak. Figuring out if you have a leak is tricky since many newer vehicles may not be equipped with fluid dipsticks in them that allow you to check your transmission fluid level. Visiting a qualified transmission maintenance and repair center is your best and safest bet to properly check your transmission fluid level.

Low transmission fluid will eventually lead to overheating, which can cause catastrophic damage. Overheating can also lead to a lack of hydraulic pressure in your transmission, which could cause your transmission to slip and struggle when it tries to engage and change from one gear to the next. This causes parts and friction material to wear out rapidly.  The quicker you discover the cause and correct it, the less expensive the repair will be.

You should also find out how often your vehicle's manufacturer recommends replacing your transmission fluid and filter. Dirty, contaminated, or old transmission fluid will damage your transmission rapidly or over time, depending on the severity of neglect. 

Be mindful to replace your transmission fluid more often if you tow with your vehicle, carry heavy loads, or live in an area with rugged or hilly terrain, stop-and-go traffic, or severe weather. Most vehicle manufacturers will provide extreme service recommendations that are more often and for less mileage for those vehicles operating in such conditions.

2. Transmission Clutches and Bands 

All automatic transmissions have friction clutches, and many also are equipped with friction bands that are essential friction devices used to hold and drive parts to shift various gears in a transmission. Those clutches and bands are very dependent on clean, cool, and full transmission fluid to stay strong and firmly engaged to operate correctly and avoid a slipping or harsh shifting transmission.

Over time, clutches and bands in your transmission can break or wear due to fluid contamination and the stresses put on your vehicle’s transmission and driveline. The only way to repair this problem is by bringing your vehicle in for service and rebuilding or replacing the transmission. Older transmissions had some adjustments for the transmission bands, but transmissions built in the last 30 - 40 years depend entirely on hydraulics pressures, valves, solenoids, and computerization to keep them adjusted.  

Automatic transmission clutch and band friction plates are paper-thin. If the transmission is not maintained with fluid changes and service inspections, the friction material on clutch plates and bands can wear out over time, leading to transmission slipping.

3.  Valve Body

The transmission is equipped with a device that is almost like a human heart. It comprises many tiny passages, valves, solenoids, and temperature sensors.  Controlled by the computer, this valve body directs the fluid to the clutches, bands, and other essential parts to provide when the transmission should go into Park, engage in a gear, shift, or downshift. This valve body has many sliding valves that look like a metal rod with pieces cut out of it along its length. These missing pieces align with a passage letting fluid flow in that direction. These valves are typically controlled by computer-controlled solenoids or by the shift lever on your console or steering column. When the transmission valve body begins to wear in the area where these valves slide, fluid escapes to incorrect places, creating slippage or shifting problems. This very common problem occurs because of age and lack of maintenance. Dirty fluid acts like sandpaper wearing the bores and valves. 

4. Gears

The gears in your transmission are called planetary gear sets, made up of a central sun gear, planetary gears that surround the sun gear, and a ring gear around the planetary gears. They play an essential part in compounding ratios that allow you to go faster and put your vehicle into reverse.

Transmission gears are designed for strength and durability. Still, with all of these complex gears constantly meshing together, they can break and wear down over the years like any other component in your vehicle if not maintained and operated correctly.

When your planetary gear set breaks, they won't mesh properly with the companion gears for a secure, perfect fit. Broken and worn gears will need to be replaced. Once you have damage to metal gears, the metal that breaks or wears off travels through the transmission and into solenoids, valves, and passages, which causes other major problems.

5. Solenoids

The solenoid is an electrohydraulic valve that acts a bit like a gatekeeper, controlling how much transmission fluid is allowed to pass through your transmission at any given time. 

If any of the solenoids in your transmission are worn, damaged, clogged, or if there have electrical issues, problems can occur. Failing solenoids may allow too much transmission fluid or too little transmission fluid to pass through your transmission's shifting passages and pressure controls, leading to various problems, including the transmission not shifting, overheating, and slipping.

6. Torque Converter

A torque converter is a component that transfers rotating power from the engine to the transmission. It uses a fluid coupling to multiply the engine's torque and provides a smooth transition between the engine and the transmission. The torque converter also is equipped with solenoids, valves, and clutch material that locks the converter during overdrive or final gears.   The torque converter also helps to dampen vibrations and reduce noise.

If a torque converter malfunctions or fails, it can cause an excessive amount of heat to build up inside a transmission, chatter, slip, and damage the rest of the transmission. 

Stop Transmission Slipping Today

If your transmission is slipping, find a certified transmission professional, such as the experts at AAMCO. For over 50 years, customers have trusted our expert technicians and quality repair to get them back on the road quickly and safely. Locate a service center near you to schedule an appointment today!