Does a Rebuilt Transmission Need to be Broken in?

When you rebuild a transmission, the last thing you want is for it to fail prematurely. But do you know how to ensure that your transmission will last?

Many mechanics and car enthusiasts swear that it’s essential to break in a new or rebuilt transmission in order for it to reach its full potential. Is this true? In this article, we’ll take a look at the facts and provide some useful tips on breaking into a rebuilt transmission.

What does breaking in a rebuilt transmission mean?

Breaking in a rebuilt transmission is when you drive a car after the transmission has been replaced and you try to minimize the strain on the new transmission.

After a new transmission is installed, the fluid and filter are replaced. The fluid should be changed again after the first 1,000 miles of driving. After breaking in your rebuilt transmission, it is recommended to change the transmission fluid every 15,000-30,000 miles or so.

What are the components of a rebuilt transmission?

The components of a rebuilt transmission include the torque converter, dipstick, pan, and filter. Also included is a new clutch set, solenoids, pressure regulator, bearings, and seals.

A rebuilt transmission is put together using parts that have been tested and cleaned thoroughly. All internal parts are tested to be sure they work properly.

Does a rebuilt transmission need to be broken in?

You do not have to break into a rebuilt transmission. The reason that new transmissions need to be broken in is that the surfaces of the gears and the bearings are not yet perfectly smooth.

As you drive the car and the gears shift, they continue to wear down until they’re perfect. This process can take thousands of miles.

Rebuilt transmissions are different from new transmissions because they have already been broken in. The surfaces of the gears and bearings have already been worn down by a previous owner, so there’s no need for you to break them in again.

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You can simply drive your vehicle as you normally would, enjoying the benefits of a rebuilt transmission right away.

Why should I break into a rebuilt transmission?

You should break in a rebuilt transmission to ensure that the internal components are properly seated and that all of the seals have been set.

Breaking in a rebuilt transmission also ensures that it will be able to handle high temperatures without issue, and reduces the risk of experiencing leaks and other issues.

How to break in a rebuilt transmission?

Knowing how to break in a rebuilt transmission is important to the life and health of your transmission. Transmission rebuilding can be a time-consuming task, but it’s well worth the time and effort.

A rebuilt transmission will last longer, perform better, and have fewer maintenance problems than one that has not been rebuilt. The following tips will help you get the most out of your rebuilt transmission:

Know what type of transmission you have. Different types of transmissions are broken indifferently. For example, manual transmissions should be broken in differently than automatic transmissions.

Older transmissions may need special tools and procedures to be properly broken in. To know how to break in your rebuilt transmission, start by knowing what type of transmission you have.

Use the right fluids for your transmission. The fluid used for breaking in a rebuilt transmission depends on its type.

Manual transmissions usually need gear oil or engine oil for breaking in, while automatic transmissions usually require regular automatic transmission fluid (ATF).

Break in your rebuilt transmission slowly at first. Many people make the mistake of driving their new car with a freshly-rebuilt transmission as if nothing was different about it. This can cause serious damage to your new or rebuilt transmission, so avoid this mistake!

What to do if your rebuilt transmission fails?

If your rebuilt transmission fails, first check the warranty. Many rebuilt transmissions come with a one-year warranty, but warranties can vary from company to company.

If you’re still within that window, call the company that provided the rebuilt transmission for you and let them know about the issue. If your warranty period has run its course, it’s time to start researching what might have gone wrong.

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Look up the specific make and model of the vehicle you were driving at the time and comb through any recall or safety issues that may have been associated with the transmission. If you see something that matches up, contact your local dealership or auto repair shop.

In some cases, it is possible for a rebuilt transmission to fail outside of the warranty period due to an error on the part of the rebuilder—even if there were no recalls on your model in place at the time of the rebuild.

If you believe this is what happened in your case, first consult a mechanic or auto expert who can confirm your suspicions; once you’ve done so, consider reaching out to a lawyer who specializes in vehicle defects.

What is the best way to break in a rebuilt transmission?

There are three ways to break in a rebuilt transmission. Before you read about them, keep in mind that there are four rules for any transmission:

  • Do not use the transmission for the first 25 miles.
  • Do not shift through all of the gears.
  • Drive at moderate speeds (avoid racing).
  • Avoid stop-and-go traffic and hills to reduce clutch slippage.

Now onto the methods:

  • The first method is to drive short trips until you’ve accumulated 100 miles on your transmission. Then change the fluid, filter, and gasket by draining the old fluid and refilling your transmission with new oil. For two days, take it easy on your car and avoid taking it up to high speeds or moving through all of the gears quickly, but after that go ahead and treat the car like normal for a couple of months before changing out your transmission fluid again.
  • You can also use an engine break-in oil additive when you drain the old fluid from your rebuilt transmission and add new oil during your rebuild process. This will help prevent metal shavings from damaging your new parts as they wear down during those first few hundred miles of driving after the rebuild is complete.

How many miles should a rebuilt transmission be driven before it’s broken in?

Rebuilt transmissions should be driven 50 to 100 miles before being broken in. The process of breaking in a rebuilt transmission involves shifting between gears at varying speeds to help your transmission’s parts become accustomed to their new positions.

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After you’ve driven the recommended 50 to 100 miles, you can shift into the park and let your transmission cool down for 30 minutes. Then, you can do what’s called a “hard brake stop” to break in your transmission.

A hard brake stop is simply when you accelerate your vehicle to about 40 miles per hour and then apply your brakes until the vehicle comes to a complete stop.

After these steps, take it easy on your vehicle for the next 500 miles—avoid aggressive driving and fast starts—and make sure that you check your transmission fluid regularly.

For more detailed information about how to break in a rebuilt transmission, consult with an auto repair professional or read the owner’s manual for your vehicle.

When should a rebuilt transmission be broken in?

Your rebuilt transmission should be broken in within 1,000 miles of the installation. This will ensure that the transmission is properly lubricated and has a chance to settle into its new home. Be sure never to exceed speeds of 55 mph during this time.


In conclusion, a rebuilt transmission does not necessarily need to be broken in. However, we do recommend it. Every transmission builder and manufacturer recommends that their transmissions are broken in at a very low RPM level before normal driving takes place.

The reason why this break-in process is important is that it enlarges the clearances within the transmission so that the fluid has a smooth trip throughout the entire unit.

This allows for more efficient operation of your rebuilt transmission at highway speeds and a longer lifespan of your automotive investment.

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