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Is Your Transmission Slipping? Here’s Why, and What to Do

Mia Bevacqua
March 7, 2018

You step on the gas pedal, but something’s wrong. The engine revs, but the car doesn’t go faster. This happens when your transmission is slipping. Transmission problems often result in a big repair bill, so you start worrying. What should you do? 

transmission slipping

If you know how to properly check your transmission fluid level, and add fluid, try that first. If that doesn't help, the next step is to get your car to a mechanic, who can diagnose the problem. You might not need to shell out big bucks — but if you wait on it, you almost certainly will.

How your vehicle’s transmission works

The transmission has one main responsibility: transmit the power from the engine to the wheels so they can move the vehicle. The energy required to get the car moving and keep it going varies, and the transmission makes this easier by using gears. Low gears are for low speeds; as the car gains speed, it uses higher gears. 

With manual transmissions you manipulate the gears using the clutch and gear shifter. You start in first gear, cycle up as you gain speed, and then back down as you slow.

All that work is taken care of for you with an automatic transmission. While your job as the driver becomes easier, the automatic transmission is anything but simple. Using a various sensors and solenoids, a computer and hydraulic power, the automatic transmission will identify the correct gear required and shift into that gear on its own. 

Reasons the transmission is slipping

If your transmission is slipping, it doesn’t necessarily mean it’s falling apart, but it does mean that it needs maintenance urgently. These are the most common causes of transmission slippage:

  • Bad fluid level or condition
  • Lack of internal pressure
  • Worn holding devices
  • Electronic control problems
Get it diagnosed by a professional
 

Transmission fluid level and condition

Low fluid level: Automatic transmissions depend on pressurized hydraulic fluid. A low fluid level can result in lack of pressure, preventing the gears from engaging like they should. This often results in transmission slippage.

Solution: A transmission doesn’t “burn” fluid the way an engine can burn oil. A low transmission fluid level means there is a leak somewhere. You might see red fluid on the ground under your car. Your mechanic can find the source of the leak and repair it. Once that’s taken care of, the transmission fluid can be refilled, and you can road-test your car to make sure the issue has been resolved.

Dirty transmission fluid: Metal debris and other contaminants can build up in dirty transmission fluid. This can cause a lack of pressure, preventing the gears from engaging. Dirty automatic transmission fluid can appear orange-reddish or reddish-brown.

Solution: Replace the transmission fluid and filter (if your car has one). Test the car to make sure that solves the problem.

Lack of internal pressure

Worn transmission pump: The transmission pump supplies pressurized hydraulic fluid to the transmission. A pump that is damaged or worn can result in a lack of internal pressure and transmission slippage. You may hear a whining noise, or notice a fluid leak.

Solution: Typically, the transmission must be rebuilt or replaced when the pump fails. That would be an expensive repair. The lack of pressure created by the faulty pump causes the transmission clutches and bands to slip and burn. This often results in debris contamination and subsequent damage to the transmission. 

Faulty valve body: The valve body directs fluid to internal transmission components. A problem inside the valve body can prevent adequate fluid from reaching the transmission bands and clutches. 

Solution: Sometimes the valve body can be replaced by itself. In most cases though, the transmission will need to be rebuilt or replaced. 

Internal fluid leaks: Fluid leaks inside the transmission can come from sources such as damaged seals. This can cause a lack of pressure and make the transmission slip.

Solution: Typically, the transmission must be rebuilt or replaced when there’s an internal leak. 

Worn holding devices

Deteriorated clutches and bands: Clutches and bands are made from friction material. In some cases, these devices simply wear out, causing transmission slippage.

Solution: On some vehicles, bands can be adjusted to compensate for wear. In most cases though, the transmission must be rebuilt or replaced. This is because debris from the bands or clutches can damage the rest of the transmission. 

Electronic control problems

Faulty solenoids: Electronically controlled solenoids regulate the flow of hydraulic fluid for shifting. Solenoids also control transmission fluid pressure and other internal operations. A problem with one or more of the transmission solenoids can cause a lack of pressure and transmission slippage. 

Solution: Sometimes, faulty solenoids can be replaced by themselves. Other times, they are integral to the valve body and the entire unit must be replaced. The transmission also could get damaged from the slipping this problem creates. In this case, the transmission may need to be built or replaced.

Transmission control module circuit problems: The transmission control module (TCM) is a computer that receives input from several sensors in your vehicle and uses it to direct the transmission. A problem with the TCM, its circuit or one of its input sensors, can result in improper solenoid operation. This can cause the transmission to slip.

Solution: In some cases, reprogramming the TCM may fix the problem. If not, the TCM control circuit or faulty sensor will need to be repaired or replaced.

What to do about a slipping transmission

Once the mechanic has diagnosed the issue, he or she can tell you whether your transmission needs to be rebuilt or replaced. Both of these will cost a lot of money. Consider getting a second opinion. If that confirms the worst, you’ll have to decide whether it’s worth it or if you should get another car instead. Get an estimate from your mechanic for the transmission work. Then figure out what your vehicle will be worth, both with and without a functioning transmission. If you have an older vehicle with lots of miles on it, it may not be worth fixing.

If you do get your transmission repaired or replaced, in most cases, the torque converter should also be replaced, and the transmission cooler flushed.


Mia Bevacqua

About the Author

Mia Bevacqua is an automotive expert with ASE Master, L1, L2 and L3 Advanced Level Specialist certification. With 13-plus years of experience in the field, she applies her skills toward writing, consulting and automotive software engineering.

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