How Long Does A Transmission Flush Take? [Save A Ton Of Money]

In this guide, I’ll explain how long does a transmission flush take. As a car enthusiast like me, you will be well aware of transmission oil change requirements. The recommended service interval for vehicle transmission fluid flush is typically 30,000 miles or every 3 to 4 years, depending on your vehicle model. However, transmission fluid can be changed any time it starts to look dirty, or as soon as your transmission starts shifting hard.

Transmission flush is a clean and easy job compared to the transmission servicing job as transmission flush only involves pumping the fresh transmission fluid through transmission cooling lines. Transmission flush will take around less than an hour if you’re not changing the transmission filter. In addition, if proper transmission flush and servicing are performed i.e. adjustment of clutch bands, cleaning of the transmission pan, and inspection of valve body, transmission flush could take 3 to 4 hours. Before transmission flush, you should first check the color of the transmission fluid. If it is too dark, clumpy, and has suspended impurities, you should avoid transmission flush, and only do transmission oil and filter change.

Why Transmission Fluid Wears Out?

Transmission fluid is a viscous liquid designed to act as a lubricant. It is used in automatic transmissions to prevent the friction in the transmission from creating excessive heat. The transmission fluid wears out due to its exposure to intermittent high heat loads under specific driving conditions. 

A transmission is a complex mechanism, but at its core, it consists of two basic parts: a torque converter (a mechanical device), and a drive train (the rest of the gearbox and engine). The transmission fluid lubricates the components inside the transmission and keeps them cool.

The fluid is constantly being forced through the transmission to lubricate the transmission parts, absorb the heat and maintain an optimum pressure inside the valve body to engage clutches and shift gears. The fluid in automatic transmissions oxidizes and breaks down over time just like any other lubricant when working in extreme temperatures. In addition, the constant contact between the gears in the drivetrain produces small metal shavings that can cause a lot of damage to the rest of the transmission.

As the transmission fluid loses its viscosity over time, it can’t provide enough lubrication to the clutch pack. As a result, transmission fluid will heat up very quickly, and it will cause clutch pad material to wear out. 

What Is A Transmission Flush?

Transmission flush simply means pumping the fresh transmission fluid under pressure through transmission cooler lines to replace the dirty transmission fluid inside the transmission system (torque converter, transmission pan, valve body, and clutch packs) with fresh transmission fluid.

The procedure involves removing the transmission pan, torque converter, and valve body. Flushing the transmission fluid will remove any debris which may have entered the transmission system.

Transmission flushes are usually recommended every two years, or as recommended by your vehicle manufacturer. They are also a good way to make sure that your transmission is working correctly.

A transmission flush costs roughly $100 – $250, depending on the vehicle.

What Happens During A Transmission Flush?

In a transmission flush, 100% of the old and dirty transmission fluid, in which metal shavings and other particles are suspended, is replaced with fresh transmission fluid. This is done to ensure that the transmission fluid is clean and does not contain harmful elements that could affect the internal parts of the transmission.

A proper transmission flush includes a thorough inspection of the transmission fluid and filter(s) (if applicable), a check for leaks, and a visual inspection of the transmission pan for rust and other signs of wear.

What Is The Difference Between Transmission Flush and Transmission Oil Change Service?

The main difference between a transmission flush and a transmission oil change is that a transmission flush involves pushing the fresh transmission fluid through the transmission back and forth while a transmission oil change involves draining the transmission fluid from the transmission pan by simply opening the drain plug.

Transmission oil change only involves draining the transmission oil from the transmission and replacing the filter, while transmission flush also involves replacing the dirty transmission fluid in the torque converter with fresh transmission fluid.

Transmission oil change and servicing only removes 1/3rd of transmission oil as the remaining transmission oil is still present in the torque converter and transmission cooler. In transmission flush, service companies do not drop the oil pan. They just run fresh transmission fluid through the transmission cooler lines of the transmission and replace it with 100% of the old transmission fluid.

Whether your vehicle needs transmission flush or transmission change service, you can find it in your owner’s manual. It is mandatory to change transmission fluid every 30,000 miles or every 3 to 4 years. But the requirement of transmission flush is dependent on your vehicle’s model.

Signs You Need A Transmission Flush

• The transmission fluid color is reddish brown or yellow after wiping the transmission dipstick with a white piece of cloth.
• Transmission shifts hard, especially when it is cold.
• Transmission is jerky due to the clutch slipping.
• Groaning noise is coming from the transmission.

Transmission Flush Good Or Bad?

Transmission flush can only be bad and cause damage if the color of the transmission fluid has become dark black due to not changing of transmission fluid at recommended intervals. 

If your vehicle has high mileage, and transmission fluid has not been changed for a long time, it will have metal shavings and small chips of clutch pad material suspended in it. The suspended chips of a clutch pad material will helo clutches engage and maintain the grip. If you perform a transmission flush at this stage, two damages will occur to the transmission:

• The clutch will slip because the fresh transmission fluid will not have any material suspended in it to engage the clutch.
• The metal shavings hanging out in the transmission pan and microscopic debris in the transmission will be forced back into the valve body, solenoids, and clutch packs, thus blocking the oil from properly applying pressure to the band.

Due to the above two reasons, transmission flush has established a big myth among car owners that it will damage the transmission. If you never let the transmission fluid become too dirty and dark, transmission flush won’t harm your vehicle’s transmission system.

Moreover, some transmission service companies use high-pressure flush machines to pump fresh transmission fluid through the transmission and replace it with the old one. These high-pressure transmission flush machines may not meet the manufacturer’s specifications and can damage the delicate internal passages and seals of the transmission valve body. This type of transmission flush is called a power flush, which I won’t recommend to you for your vehicle.

Best DIY Method To Perform Transmission Flush

To save a big chunk of your money, in place of using a flushing machine that produces high pressure in the transmission lines in order to flush away the old transmission fluid, I would recommend you perform a regular transmission flush that uses the power of your transmission’s gear pump. 

You should perform the following steps for transmission flush:

1. First, check the health of the transmission fluid. If it is reddish brown or yellow colored, it will be fine to perform a transmission flush. If transmission fluid is dark black and you can observe suspended particles, you should only do an oil and filter change for your transmission. You should use a white wiping cloth to observe the color of the transmission fluid.
2. Remove the transmission pan and clean it thoroughly. Some transmission pans have magnets to catch the metal shavings. Clean the transmission pan with a brake cleaner.
3. Also, clean the transmission filter.
4. Fix the transmission filter and tighten the transmission pan.
5. Now, locate the transmission cooler inlet and outlet lines. The location of those lines entirely depends on your vehicle’s model. You can take help from the owner’s manual to find them. The transmission cooler lines are located near the radiator.
6. After you locate the transmission cooler lines, it might be difficult to tell which is the inlet line (this line carries transmission fluid from transmission to the cooler) and the outlet line (this line carries cooled transmission fluid from the cooler back to the transmission). You can take two rubber hoses and attach them to the hoses that go into the transmission cooler lines. Put the opposite ends of those two hoses in the bucket and start the engine. The hose that spits out the transmission fluid is the one that goes from the transmission into the cooler. I found this video clip on finding the transmission line that goes into the cooler helpful.
7. After confirming which transmission hose goes into the cooler, disconnect it from the cooler and connect it with a rubber hose.
8. Take a bucket and put the opposite end of the rubber hose into the bucket to collect the old transmission fluid.
9. From underneath the hood, find the transmission oil dipstick and remove it. 
10. Take a long funnel and put it into the opening where the transmission dipstick goes.
11. Take a bottle of transmission oil recommended by your vehicle’s manufacturer. Make sure that the bottle of transmission oil has recommended capacity. For instance, Ford 150 needs 14 quarts of transmission oil during transmission flush.
12. Start the engine and gradually add the fresh transmission oil through the funnel.
13. Meanwhile, you will be observing bad transmission fluid flowing out of the hose in the bucket.
14. Keep on adding the fresh transmission fluid until you see the color of the transmission fluid color change from yellow or reddish brown to a clean red.

Frequently Asked Questions About Transmission Flush