ProCarReviews is reader-supported. We may earn commission on sales through our links at no extra cost to you. View policies.

The Best Transmission Additive 2021

Transmission Additive For Hard Shifting

Slipping transmission or hard shifting are very common issues, which can be expensive to fix. However, using a transmission additive may be an affordable solution that solves the issue and is far cheaper than replacing the transmission.

The best transmission additive is the Lucas Transmission Fix, which cleans and lubricates sticking valves for proper shifting.

Replacing your transmission fluid can solve many issues but using an additive for your transmission is a quick and easy solution. They contain a mixture of friction modifiers and other petroleum additives that mix with the current transmission fluid.

Table of Contents

Transmission Additive Comparison

Transmission AdditiveSpecialitySize
Lucas Transmission FixSlipping Transmission24 oz
Lubegard Dr. TrannyShudder Reduction2 oz
Prolong Super LubricantsAutomatic & Manual8 oz
Sea Foam TT-16 Trans TuneSticky Valves16 oz
XADO Revitalizant EX120Shudder Reduction0.28 oz
Liqui Moly 20040Protection6 oz
zMax 51-306Hard Shifting6 oz
K&W Trans-XHigh Mileage16 oz

Driving with a faulty transmission that shudders or slips is not pleasurable and will eventually causes long term damage. Tackling the issue with an oil additive is not a long term fix but can solve the issue and allow gears to change more smoothly.

During heavy towing or lack of servicing, the fluid can deteriorate and breaks down into a sludge form, which causes issues. Using an additive helps restore the original properties of the fluid, which resists heat and provide frictional properties.

Below is a list of the best transmission additives that will help reduce hard shifting, sticky valves and and slipping transmissions.

The Best Transmission Additive

1. Lucas Transmission Fix

Lucas produce some of the best oil additive products available and have a reputation for great results. This additive has been designed specifically for slipping transmission issues and stops leaks or hard shifting completely.

Features of the Lucas Transmission Fix additive include:

  • 100% solvent free formula
  • Prevents foaming
  • Lowers the operating temperature of the fluid
  • Stops most seal leaks
  • Renews worn fluid
  • 24 oz bottle for multiple uses
  • Requires no draining and can be added straight into the current fluid

The Lucas Transmission Fix formula forms a polymetric film, which renews worn bands to stop the transmission slipping. This process controls overheating and renews fluid that has become worn from heavy hauling. Overall, it is the best additive for a slipping transmission and offers great value for money.

Check it Out

2. Lubegard Dr. Tranny Instant Shudder Fixx

The Lubegard transmission additive is by far the most popular. It is designed to eliminate the torque converter from the dreaded lock-up shudder. This is achieved by a concentrated friction modifier, which is in a small 2 oz bottle.

Features of the Lubegard Dr. Tranny Instant Shudder Fixx include:

  • 4 times less wear than regular ATF
  • Voted the best by transmission professionals
  • Eliminates transmission shudder issues
  • Suitable for an automatic transmission only

The 2 oz Lubegard formula will instantly resolve transmission shudder and can be used in both conventional and synthetic oils. However it not only cleans the transmission but it also acts as a protectant to help improve the longevity.

Check it Out

3. Prolong Super Lubricants Transmission Additive

The Prolong Transmission Treatment is an additive that can be used with both automatic and manual transmissions. The formula ensures that all molecules chemically bond with metal surfaces in order to provide a protective layer that reduces friction and heat.

Other features of the Prolong Super Lubricants Transmission Additive include:

  • Promotes smooth and more responsive gear changes
  • Suitable for both low and high mileage cars
  • Protects against heat and friction
  • Compatible with all common transmission fluids
  • One bottle will treat a complete transmission

Overall, it is an excellent all-rounder that can work with both manual and automatic transmissions. The Prolong Super Lubricants formula cleans, lubricates and provides great protection, which is everything you would want in a transmission additive.

Check it Out

4. Sea Foam Trans Tune Transmission Additive

Sea Foam is a very reputable brand and the Hydra Trans Tune is their highly rated automatic transmission additive.

The brand claims that the quick action formula helps to clean sticky valves, dry moisture and improve the overall performance of your transmission.

Other features of the Sea Foam Trans Tune include:

  • Suitable for automatic transmissions
  • Can also be used in power steering and hydraulic pumps
  • Remove moisture and deposits
  • Clears varnish present within the transmission
  • Reduces erratic and hard shifting
  • Does not soften or swell O-rings

Overall, the Sea Foam Trans Tune is the best transmission additive for the money that is produced by a trusted brand in the automotive industry. It is a petroleum-based formula that can be used with a range of fluids without causing damage.

Check it Out

5. XADO Revitalizant EX120 Conditioner

XADO Revitalizant EX120 has the most concentrated formula that is only available in a 8 ml syringe. It is designed to rebuild and restore metal parts of the transmission and provide protection against future wear.

Features of the XADO Revitalizant EX120 transmission additive include:

  • Eliminates surface defects
  • Protects against extreme heat
  • Stop transmission shudder, slipping and vibration
  • Suitable for automatic, CVT and semi-automatic transmission
  • Alternative formula available for manual transmissions

Due to the small dosage via the syringe, it is important that you use the required amount of additive. XADO state that for every 5 to 8 quarts of ATF, you should use 1 syringe. Overall, it is a specialist formula that is available for both manual and automatic transmissions that eliminates slipping, shudder and other issues.

Check it Out

6. Liqui Moly 20040 ATF Additive

Liqui Moly are another highly reputable brand and their automatic transmission fluid additive is a great option. The brand states that its designed to regenerate seals as well as clean and protect the internals of the transmission.

Other features of the Liqui Moly 20040 include:

  • Cleans and protects
  • Prevents hard down shifting
  • Prolongs the life of the transmission
  • Regenerate seals
  • Made in Germany
  • Can also be used for power steering applications
  • 6 oz tube

The Liqui Moly 20040 is a highly rated transmission fluid additive that is designed to clean and protect rubber or plastic seals. It also has the added bonus of helping to reduce noises coming from power steering systems.

Check it Out

7. zMax 51-306 Transmission Additive Formula

The zMax is an affordable automatic transmission formula that aims to improve performance and promote smoother shifting. The additive alters the molecular structure of the existing fluid and restores its original optimum properties.

Other features of the zMax 51-306 include:

  • Reduces varnish
  • Improves shifting
  • Reduces leaks
  • Not suitable for CVT transmissions
  • 6 oz bottle

The zMax 51-306 is an effective yet cheap transmission additive that’s actually worth buying. The brand states that its scientifically proven to improve shifting and reach all the transmission’s internal parts for the best results.

Check it Out

8. K&W TransX Automatic Transmission Additive

The K&W TransX is a relatively unique automatic transmission additive because its been designed primarily for high mileage transmissions. The advanced formula restores viscosity, lowers temperatures and stops leaks.

Other features of the K&W TransX include:

  • Designed for transmission over 75,000 miles
  • Restores smooth shifting
  • Extends the transmissions life
  • 16 oz bottle
  • Not suitable for CVT transmissions

For those that want to further extend the life of their high mileage transmission using an additive, the K&W TransX is the best option. It’s been designed specifically for transmissions over 75,000 miles and provides noticeable improvements almost instantly.

Check it Out

Transmission Additive Buying Guide

Hard shifting or a slipping transmission can completely ruin a pleasurable drive. Replacing the transmission fluid can be a solution but it may not be possible to perform the replacement. Therefore using a transmission additive would be the best option and it will restore the fluids properties and reduce transmission problems.

For those that regular haul heavy loads, you will need to pay extra attention to your transmission. The extreme heat from towing causes the fluid to break down, which can form a sludge that effects the performance.

To help you make an informed buying decision, we have produced the below buying guide regarding transmission additives.

Additive For Slipping Transmission

Common Transmission Problems Additives Can Solve

Transmission can become problematic for a whole range of reasons. However, replacing or repairing your transmission can come at a great cost, which many may not be able to afford. Considering that a transmission additive would be a fraction of the cost, it is worth trialing.

Some of the problems that an additive can resolve include:

  • Slipping transmission
  • Hard shifting
  • Sticking valves
  • Leaks
  • Shudder/vibration
  • Grinding gears
  • … and much more

If possible, we highly recommend choosing a transmission additive that tackles the exact problem that you are experiencing for the best results.

How To Add The Additive?

The way in which you add the additive to your transmission may differ from brand to brand. Some simply pour straight into the transmission fluid by removing the dipstick and using a funnel to reduce any spillages. However, there are some that may require you to drain the transmission, which many people will not be able to do.

If you want a DIY solution to your transmission problems, it is highly recommend to choose an additive that simply pours straight in.

Manual or Automatic Transmission Additive

As you may or may not already know, the fluid differs between manual and automatic transmissions. Therefore, this means that not every additive will be compatible with both types and its vital that you check the bottle beforehand.

For example, the Lucas Transmission Fix is only suitable for automatics whereas the Prolong Super Lubricants formula is compatible with both.

Transmission For Sticky Valves

Misdiagnosing Problems

It is important that you understand that the additive is not a miracle product. The same can be said with a fuel injector cleaner, it will not magically cure all your fuel problems. For example, if you have a transmission that is slipping, it may be low on fluid.

Therefore pouring an additive will not make any difference because the fluid will still be low and will require topping up.

To avoid disappointment, we recommend that you check the fluid level in your transmission. Ensure that there is adequate levels and the oil is not a burnt color.

This would indicate that the fluid may be okay and trialing an additive may be the best option. If there are any mechanical issues, the additive will not be as effective.


Adding a transmission additive to your fluid can solve all your issues and be the best product you have ever bought. However, many people believe that it is a miracle formula that can solve any issue, which is of course not the case.

All of our recommendations are suitable for a range of issues and are developed by reputable brands. We highly recommend avoiding brands that are not that well known as they would not have gone through as much proven tests.

procarreviews author

Written By Dan

About the Author

Dan is an automotive journalist and owner of over 10 cars ranging from supercars, tuned cars, classics and your good old beater cars. He always likes to get his hands dirty with nut and bolt restorations or detailing sessions using the best products on the market.

More About Our Team →


Copyright © 2023. All rights reserved.