8 Best Transmission Oil For Harley 6 Speed [Auto Expert In 2023]

The question of whether transmission oil is compatible with Harley 6 Speed has long been a subject of controversy. Therefore, when you’re looking for the best performance of your vehicle’s engine, you surely need to look for the best transmission oil for Harley 6 Speed.

High-quality transmission oil will enhance the overall performance of your vehicle and will also ensure that your engine stays more durable and require less maintenance.

So, to aid you in choosing the best transmission oil, our automotive experts have gone through many transmission oils and have shortlisted the best ones for your Harley 6 Speed. Therefore, don’t skip any of the sections and read until the end to know it all.

What Kind of Transmission Oil Should I Use in My Harley 6?

The first thing you need to know is that there are two types of transmission oils: synthetic and mineral. Synthetic oils are man-made, while mineral oils are derived from crude oil. Both have their pros and cons, but synthetic oils are generally considered to be better for high-performance applications like a Harley 6-speed.

What Kind of Transmission Oil Should I Use in My Harley 6

Synthetic oils typically provide better protection against wear and tear and can also withstand higher temperatures. They’re also more expensive than mineral oils, so you’ll need to decide if the benefits are worth the extra cost. However, it’s wise to always keep the expert’s suggestions in mind before you make a pick for your Harley Speed.

According to our automotive experts, you should always pick heavy-duty transmission oil like Spectro Oil R.HDPG for your Harley 6 series.

Spectro’s Synthetic Motorcycle Transmission Fluid is a top choice for Harley 6-speed riders. It’s a fully synthetic oil that’s designed to provide superior protection and performance in high-demand applications.

The oil is fortified with special additives that provide excellent protection against wear and tear, and it can withstand high temperatures without breaking down. It’s also compatible with all types of clutch materials, so you don’t have to worry about compatibility issues.

Overall, The most common and recommended type of oil for the Harley-6 is the synthetic gear oil. Synthetic gear oil is designed to provide better protection and performance in high-temperature and high-pressure situations, which is ideal for a transmission that is constantly under a lot of stress.

How Much Oil Does a 6 Speed Harley Transmission Take?

The amount of oil you would store to run your bike depends a lot on you and your usage. For instance, if you accelerate a lot while riding your 6 Speed, then it’s evident that your bike would take in a lot of the transmission oil and vice versa.

Therefore, you must know an initial approximate transmission oil amount for your bike before going for the ride. When filling in the transmission, the approximate fluid capacity of your speed Harley is around 24 ounces.

However, don’t mix the fluid capacity with the transmission oil. The fluid capacity is the lubricant used in the transmission, whereas the transmission oil is the fuel required to run the Speed Harley.

So, the approximate oil capacity of your Speed 6 Harley is around 3 quarts. This is the ideal amount for your Harley, and also, do make sure that you don’t overfill the transmission as it can later hinder the performance of your bike.

8 Best Transmission Oil For Harley 6 Speed Reviews

It’s time we jump into more comprehensive details of our top picks. That way, you’ll find more confidence while making the final purchase decision.

Best Transmission Oil For Harley 6

1. Best for Being Fully Synthetic: Spectro Oil R.HDPG6 Heavy Duty 6spd Trans Lube

Got a noisy Harley 6-speed? The heavy-duty platinum from Spectro is a fully synthetic lubricant specially made to eliminate all annoying noises from your Harley Davidson. Besides, it offers smoother shifting, eliminates clunks, and reduces 5th gear whine.

Spectro Oil R.HDPG6 Heavy Duty Platinum Full Synthetic

Specifications for Spectro Oil R.HDPG6

Brand NameSpectro Performance Oils
Liquid Volume946 ml
Item Weight2.08 lbs.

Harley-Davidson owners cannot simply use any lubricant on their vehicles. That’s why Spectro has introduced one of their specially engineered products for Harley and that is the heavy-duty platinum lubricant.

It is built on G-4 technology, which is combined with a few other high-quality additives making it the best transmission fluid for Harley 6 speed. With this, you can rest assured the gear life will extend.

Here, the anti-wear protection is commendable. The oil adds more film strength to your Harley’s gear teeth to reduce drag. This way, you can provide the gear with maximum protection against wear and tear. Plus, you’ll surely notice a quieter transmission.

As a fully synthetic lubricant, it protects the internal parts and makes your ride smoother than ever. You know, 6-speed Harleys are great when it comes to providing more power and efficiency.

But, they can be noisy and whiny in the fifth gear. This synthetic oil by Spectro is excellent for reducing all those noises and whining. With this oil, you can enjoy your long-distance adventures in peace.

In fact, this transmission oil has achieved the greatest traction in the Harley world due to its ability to eliminate noise from a 6-speed gearbox. Besides, the heavy-duty platinum lubricant can reduce shifting clunk. So that’s a plus if you find that irritating.

Does your bike fail to perform well when you put heavy loads on it? You can say goodbye to all difficulties while shifting gears with heavy loads by using this oil. The SAE 75w140 formulation prolongs gear life and performance under pressure and extreme weather conditions.

Thanks to the excellent formulation, whether it’s a sunny day or a freezing night, your bike will run smoothly in extreme weather conditions.

Main Features

  • A full synthetic lubricant made especially for curing noisy 6-speed transmissions
  • Compatible with any Harley, regardless of the model
  • Features G-4 technology and additional high-quality additives
  • Uses SAE 75w140 formulation to perform well under heavy loads and extreme temperatures
  • Formulated to run thousands of miles without changing the oil
What We Like
  • Provides smooth shifting
  • Reduces whining and clunks of the gear
  • Protects the metals from friction
  • Extends the gear life by preventing wear and tear
  • Because of the low consumption rate, lubricant can last a long time
What We Don't Like
  • The product is costly

Tester Notes

If you are looking for a fully synthetic lubricant that can extend the gear life of your Harley, then go with this one. You’ll enjoy smooth shifting as the transmission oil will reduce the clunks and whining of the gear. Moreover, the oil protects the metal from friction and extends its gear life by eliminating wear and tear.

2. Best for Ultimate Filtration: Maxima Racing Oils 90-119016C

If you have any knowledge about the leading oil brands, you surely have heard of Maxima Racing Oils. The company has introduced its oil change in a box, providing everything for an oil change kit. To meet all your needs, the box contains the best oils and the ultimate filtration.

Maxima Racing Oils

Specifications for Maxima Racing 90-119016C

Brand NameMaxima Racing Oil
Liquid Volume192 Fluid Ounce
Item Weight14 lbs.

First, let’s see what you get in the package. This oil change in a box contains a premium oil filter, synthetic engine oil, transmission, and gear oil, and primary oil. The complete kit is compatible with any Harley Davidson after 1999.

Here, synthetic oil is suitable for a twin-cam engine. And when it comes to V twin engines, you need to fulfill their unique needs to keep them efficient. This synthetic and mineral-based oil is the best transmission fluid for Harley 6 speed as it is engendered carefully to keep your two-wheeler components smooth and powerful on the roads.

We like the oil most because it will provide you with better viscosity than other conventional oils. High-end viscosity is a must for V twin engines to control friction and sludge inside the machine.

With its high viscosity and excellent cleaning capability, this oil will prevent wear and tear as well as engine deposits that damage the interior parts of your bike engine. To improve the cleaning ability, ultra-clean detergents are mixed in the formula of the primary oil. This means the oil will collect dirt and debris while circulating and keep the engine running smoothly.

Another highlight of this oil is its unique formulation. The engine and gear oil include a surface-active ester tech to lower operating temperatures, increase film strength, and eliminate wear to enhance the longevity of your bike engine.

The high-quality transmission oil is excellent for gear performance and protects the gears from friction as well. Extreme pressure additives are also included with the surface-active chemistry for smooth gear shifting at high speeds and under peak loads.

Overall, if your gearbox is 4, 5, and 6 speed, this transmission oil will be ideal for better and smoother performance.

Main Features

  • Oil change in a box has 4 quarts of engine oil, 1 quart of transmission oil, and 1 quart of primary oil, along with an oil filter
  • The ester-based synthetic oil is formulated and approved as a multi-compartment motorcycle oil
  • Compatible with any Harley series from 1999 to till date
  • For the formula, surface-active technology is mixed with extreme pressure additives and ultra-clean detergents
What We Like
  • Proper gear protection
  • Boosts the performance of the engine
  • Potent formula oil resists heat breakdown
  • Facilitate trouble-free functioning
What We Don't Like
  • The transmission oil and the primary oil are not synthetic

Tester Notes

If you are looking for a combo of racing synthetic oil, transmission oil, and primary oil for your Harley then choose maxima running oil. It’s a complete solution box that takes care of every component of your Harley.

3. Best for Compatibility: Red Line Oil Big Twin 20W50 PowerPack

We chose the Red Line all-in-one bundle for hardcore riders. This oil package has many great features for Harleys and other motorcycles, and you’ll be surprised to experience how significantly it reduces engine temperature, transmission sounds, and oil consumption.

Red Line Oil Big Twin

Specifications for Red Line Oil

Brand NameRed Line Synthetic Oil
Liquid Volume256 Fluid Ounces
Item Weight15.6 lbs.

We know gearbox sounds can be annoying for the riders, and to minimize the noise, this oil package can work like magic. Gearbox noises are created when a low-quality oil fails to withstand the pressure coming from the gear teeth.

The transmission oil of this package includes friction modifiers and thick oil films to reduce the shifting gear noises. Even if you journey for a long distance, there won’t be any friction inside the gearbox, and everything will be quiet and peaceful.

Talking of long distances, this package is perfect for those who want to ride miles after miles without any disturbance. A whole box includes 5 quarts of motorcycle oil, 1 quart of primary chain case oil, 1 quart of transmission oil, and 1 bottle of fuel injection cleaner.

Besides, it also has a sticker kit and a versatile funnel. So, you can guess the overall package has everything you will need to take care of the parts of your Harley and improve its performance.

Another good thing about this oil is that it doesn’t need constant changing. Thanks to the heat reduction formula, one application can go a long way. Since Harley-Davidsons are air-cooled bikes, they create more heat than other liquid-cooled ones.

The composition of this Red Line engine oil is engineered to keep the temperature low all the time, no matter how hot the weather is. As for viscosity, the high density of this oil provides a firm thickness that offers a protective layer over your bike’s gear teeth.

Hence, there will be minimal friction inside the engine, and it will last longer. Lastly, you’ll love the extra chain oil in this package. This oil has an anti-dust blend that prevents dust and sludge deposits on your motorcycle chain. It also offers a higher lubrication retention period. So, your chains will always be clean and sufficiently lubricated.

Main Features

  • Low-temperature composition works for different types of motorcycles
  • Noise-reducing formula capable of withstanding high pressure during gear shifting
  • A blend of high-quality oils boosts up the acceleration and provides extra mileage
  • The oils have high viscosity, improved lubrication prowess, and better cleaning abilities
  • Has a fuel injection cleaner and chain case oil in the packaging
What We Like
  • Works well for heat reduction
  • Cancels or reduces noise due to shifting and transmission
  • Compatible with multiple types of bikes
  • Improves shifting for the Harley
What We Don't Like
  • Expensive product

Tester Notes

Although expensive, red line oil is an excellent choice for Harley to speed up the engine’s performance while making less noise. Its low-temperature characteristics make it compatible with different types of motorcycles like Harley. Along with transmission oil, you’ll get chain case oil, fuel injection cleaner, and motorcycle oil, a complete package for your Harley. Moreover, the high viscosity of this oil enhances the lubrication power with better cleaning abilities.

4. Best for Valve Operation: RAVENOL J1D2113 ATF (Automatic Transmission Fluid)

RAVENOL automatic transmission fluid is another great invention by RAVENOL. This excellent product will make your automatic transmission work better than before.


Specifications for RAVENOL J1D2113

Brand NameRavenol
Item Weight2.05 lbs.
Model Number‎E10DB9
Liquid Volume1 Liter
MaterialSynthetic oil

The RAVENOL J1D2113 Automatic Transmission Fluid is the best budget-friendly product for Harley 6-speed engine. It is a synthetic oil that will keep your engine running smoothly and protect it against wear, corrosion, and foam formation.

Although it might seem like just a straightforward bottle, it can do a lot more than you think. The fluid is not only functional for 6-speed transmission but also compatible with 8-speed transmissions.

Its outstanding cooling properties will keep your engine running cooler even when it is at high RPM. And with the excellent anti-wear, corrosion, and oxidation properties of this product, it will keep your transmission in top condition throughout its life.

While keeping the engine cooler, this oil also helps the engine to work more fluidly. You won’t have to worry about the stability of the viscosity index while using this transmission oil, and it looks after the overall performance as well.

On top of that, the thermal stability feature will help your transmission stay more relaxed during the summer and warmer during the winter months. Also, it will help your transmission perform much better and last longer than ever before.

Furthermore, this fluid optimizes the valve operation and works as a gear lubricant as well. As the engine parts are all metal, this lubricant reduces the friction to a bare minimum, even in the frosty winter weather.

Overall, the RAVENOL ATF does the necessary things outstandingly to keep the Harley 6 in good health. It reduces the chances of oxidation and corrosion. Besides, take care of the thermal ability as well.

Main Features

  • Compatible with both 8-speed and 6-speed transmission
  • Can resist corrosion and oxidation
  • Provides smooth shifting and prevents overheating
  • Comes with great oxidation stability
  • Outstanding cooling capacity
  • Provides excellent lubrication even in frosty weather
  • Offers a stable viscosity
What We Like
  • The best product on budget
  • Synthetic oil is great for transmission life
  • Amazing cooling properties
What We Don't Like
  • The oil might be a bit costly

Tester Notes

If you want a minimalistic routine to take care of your Harley, then RAVENOL ATF is the best choice for you. This economic package is nothing but a blessing for those who want to spend less and get more. Moreover, the transmission oil is not only compatible with Harley 6-speed but also suitable for 8-speed gear. The advanced cooling capacity and stable viscosity of this oil ensure noise-free super-smooth performance.

5. Best for Heavy-Duty Performance: Life Guard Fluid 8 (7 Liter)

ZF life guard fluid is a heavy-duty synthetic fluid that performs well in Harley. It’s a great transmission oil for Harley-Davidson motorcycles and it can be used as a daily driver. Besides, the transmission oil provides the highest level of protection, hence it is well suitable for Harley-6 engines.

Life Guard Fluid 8

Specifications for Life Guard Fluid

Brand NameZF
Item Weight‎14.62 lbs.
Model NumberS671090312
Liquid Volume7 liter
Packaging7 piece set

Lifeguard Fluid 8 is a great gear oil that provides better fuel efficiency in your Harley-6’s transmission. It is made of specially formulated base oils that provide superior lubricity, reduce emissions, and ensure longevity.

Plus, the base oil is specially designed to provide maximum protection against oxidation. The additive package is composed of anti-wear, friction modifiers, extreme pressure, and anti-foaming agents to ensure optimum protection.

ZF is renowned for its high-quality transmission oil production, and the response of continuous friction ensures smooth shifting. And you may have seen some other gear oils that claim to reduce fuel consumption by up to 20%, but Lifeguard Fluid 8 is actually proven to reduce fuel consumption by as much as 30%. So, some extra mile coverage is guaranteed with this one.

Besides, the low viscosity helps to reduce noise in the transmission. Here, the fuel consumption is shallow, which means this product reduces CO2 emissions as well.

In addition, it also has cooling properties that keep the engine cool even at the highest RPM. The oil keeps the engine active and smooth in adverse weather conditions. Even at a low temperature, this oil can perform well. However, this fluid can also reduce vibration by controlling the slip of the converter clutch.

Overall, this transmission oil is specially formulated for Harley 6-speed transmissions with a semi-synthetic base oil that provides an excellent balance of viscosity at low and high temperatures. It also helps prevent the transmission’s internal parts from overheating.

Main Features

  • High-quality transmission oil
  • Compatible with 6-speed transmission
  • Reduces noise and vibration while boosting the performance of the engine
  • High-thermal oxidative stability
  • Top-tier semi-synthetic oil base
  • Individually customized additive components
  • Lower fuel consumption
What We Like
  • Cheap price
  • Superior quality fluid
  • Amplify transmission life
  • Can perform well in adverse weather conditions
What We Don't Like
  • Replacement is not easy

Tester Notes

ZF has one of the best transmission oils in the market right now. So, if you are looking for the best transmission fluid for Harley 6 speed at an affordable price and want to enjoy smooth and consistent shifting in your Harley 6-speed transmission, you should definitely check out ZF LifeguardFluid 8. Moreover, you’ll love its cooling properties, lower-fuel consumption, and thermal-oxidative stability, as they will ensure superior performance with your Harley 6 speed.

6. Best for Shockproof Technology: Red Line RED42804 V-Twin Transmission Oil

Improving your vehicle’s performance is something this transmission oil master at. With this transmission oil, you’ll get enhanced performance with reduced temperature and noise. So, if you’re looking for a transmission oil that would be compatible with most vehicles, pick this one. Check out the rest below.

Red Line RED42804 V-Twin Transmission Oil

Specifications for Red Line RED42804 V-Twin

Item weight1.7 pounds
Liquid Volume128 Fluid Ounces
Fit typeVehicle Specific

It’s delightful news that this oil is designed with shockproof technology, proving to be the safest deal for us. This technology will always get you and your vehicle out safely during extreme situations, and such cutting-edge technology can save you from any misery.

We know how irritating the shifting drive shaft noise is, and the way this oil confines the noise that notorious shifting bothers you with by shifting clunks found in the gearboxes is actually remarkable. We bet none other transmission oil would be able to work in such a smoother way to change the shaft rapidly without any noise.

Drops down the extreme temperature to the lowest with the increased benefits and transmission fluid from this oil, even though it’s a really thick oil. No worries about high temperatures making you go through dangerous accidents as long as it has got your back.

It has been made with a thicker formulation for resisting throw-up and even for filming between gear teeth for better performance. And the flattering fact is the gear teeth put decent impacts on raising the speed to the fullest safely while using this oil.

While finding a transmission oil that is obliged by all the high-revving conditions, this one literally goes with all the latest four-stroke motorbikes and sport bikes. It is eligible for a few other vehicles so that you can get multiple tasks done by this one transmission oil.

Whether it’s a big impact or small, all can be dealt with this oil that contains transmission fluid to provide better protection while offering twin 6 speed, on the other hand.

Main Features:

  • Features shockproof advanced technological design
  • Works on reducing the notorious shifting clunk
  • Provides thicker oil films
  • Shows compatibility with the latest high-revving four-stroke motorbikes
  • Contains transmission fluid
What We Like:
  • Can totally shut transmission noise off
  • Helps your vehicle provide better performance
  • Specially engineered to offer the most compatibility
  • Gets you better milage
  • Pocket friendly even though it meets all our requirements
What We Don't Like:
  • Average smoothness
  • Not good with clunks

Tester Notes

We want you to get something for you that is stable and offers sharp edge technological support, quieter and hassle-free shifting, compatibility, and protection. This oil can meet all those requirements, and giving this a shot would be highly beneficial.

7. Best for Comfort: Mobil (112812-4PK) Delvac Synthetic Transmission Fluid

Everyone wants the best out of their vehicles. If you invest in this transmission oil, we can assure you immense comfort and better than ever performance. Excellence lies in purchasing this oil to enjoy the most reliable journey with your vehicle.

Mobil (112812-4PK) Delvac Synthetic Transmission Fluid 50

Specifications for Mobil (112812-4PK)

MaterialsCopper, Synthetic
Item weight31.9 pounds
Liquid volume128 Fluid Ounces
DesignWear & Tear protection
Fit typeVehicles

An oil with anti-wear capacity, without any doubt, offers the best performance of all times, and this one from Delvac ensures everything that you can expect from transmission oil. Besides, its EP performance and load-carrying capacity are highly obsessive.

If you desire to get complete protection from corrosion of copper, then we find this oil to be the best pick for you. You’ll get maximum protection with deposit formation and thermal and oxidation protection.

Convenience comes along with a stable shear design, and that’s what you get with this oil, ultra shear- stability. On the other hand, you get heavy-duty transmission benefits to deal with extreme situations easily.

Fluid-50 quality of this good showers you with convenience by providing sulfur-phosphorus oil type, oxidation stability, corrosion control, increased performance, and whatnot. You get to overcome freezing temperature situations with this oi as well.

While looking around a bit about this oil, the most eye-catching yet effective fact about this you’re going to notice is its noise and temperature controller capability while shifting.

Hence it makes you go through the smoothest experience regarding shifting. Most oils can offer you to keep the temperature down, but this oil is specified to be an expert at providing high-temperature performance.

The importance of suitable quality materials is above all. This oil has excellent quality materials to offer as well, and better materials mean more extended service. The manual transmission lubricant in this oil is always ready to face increased drain by reaching OEM requirements.

Mainly, it’s formulated so that the oil can make your vehicle catch up with a wide range of environments with duty-on and off-highway equipment.

Main Features 

  • Higher load-carrying capacity
  • Comes with 3x better protection system against deposit formation
  • Offers you better oxidation protection
  • Unbelievably stable shear system
  • OEM Warranty requirements certified
What We Like
  • Helps you with ultra noise reducing power
  • Convenient with temperature reducer
  • Offers maximum protection against every extreme situation
  • Outstanding performance along with speed
  • You can cross some extra mileages
What We Don't Like
  • Low-key expensive
  • It might make you face storing issues

Tester Note

If you’re a bit high on budget and want the safer yet more efficient transmission oil, you can totally rely on this one and its beneficial performance. With this one transmission oil, you get maximum protection, shear stability, durability, and reliability.

8. Best for Stability: Lucas Oil Synthetic SAE 75W-140

Who doesn’t want a reliable companion for their vehicle? With Lucas transmission oil, your vehicle will offer better performance, shear stability, thermal and oxidation protection, and whatnot. If we don’t mention its excellent anti-wear and EP performance, it will be a crime.

Lucas Oil Synthetic SAE 75W-140 V-T

Specifications for Lucas Oil Synthetic SAE 75W-140

MaterialsCopper, Synthetic
Item weight1 pound
Liquid volume32 Fluid Ounces
DesignCooler & Quieter
Fit typeVehicles

You probably have gone through one of those situations when your vehicle gets extremely hot while shifting? That’s a dangerous deal, and that’s precisely why you should rely on this oil that keeps the gears at a proper temperature at any cost.

A vehicle requires advanced cooling technology to go through extreme high-temperature situations. You can expect reliable high-temperature performance from this oil.

Say bye-bye to those days when you had to tolerate all the inconveniences because of extreme noise while shifting. The satisfying fact is this oil shuts the noise up deeply.

Not only shockproof, but this oil can also offer you 3x better protection benefits to save you against anything that can come along with the roads. Moreover, you’re allowed to handle both duty-on and off-highway situations with this oil.

The way it turns the gear system would feel like the smoothest shifting system ever because that’s what it offers. Hence, handling gears and clutch stuff becomes easier with this oil.

While shifting, it works quickly and smoothly so that the vehicle makes no noise. Drive shaft shifting becomes easier with the intelligent design of this oil.

It helps the mileage to increase so rapidly that it will be difficult for you to believe. While offering your automobile HD multiple speed improvements, the oil gives you unparalleled performance.

It doesn’t offer a thin formulation that can’t film between the gear teeth of your vehicle. The thicker formulation obviously puts a significant impact on the performance level and saves you from potential dangers.

Main Features

  • Offers enhanced shear stability
  • Formulated with suitable quality materials
  • Designed to be cooler and quieter
  • Technological support for better performance
  • Higher shifting safety standards
What We Like
  • Provides enhanced protection
  • Reduces noise and temperature
  • Make shifting easier
  • Smoother and quieter performance
  • Gets you a better clutch grip
What We Don't Like
  • Average thickness
  • Not compatible with most vehicles

Tester Note

Handling any extreme situation becomes way easier with the organized performance from this oil. It offers you better performance and shear stability with appropriate protection.

How to Choose the Best Transmission Oil for Harley 6 Speed

You can’t just pick any transmission oil for your Harley 6 Speed since there are so many aspects to consider before making your decision.

How to Choose the Best Transmission Oil for Harley 6 Speed

Therefore, to aid you with this troubleshooting, our automotive experts have listed all the significant factors that you need to consider to ensure the best performance for your Harley 6 Speed.


You have to check the selected oil’s viscosity and know how it can benefit your Harley bike. So, you must choose a thick oil that lubricates the motor for a long time, and the overall flow is also remarkable. Moreover, you must also ensure that your transmission oils don’t stick to any engine compartments whatsoever.


That’s another thing that you must consider while buying transmission oil. Temperature plays a crucial role in ensuring the performance of your vehicle. Therefore, always check the labeling on the product before you buy it. If you still face issues, you can always consult with the manufacturer regarding this, and they will help you pick the one you need.

Expert’s Tip: 10W-30 transmission oil performs the best in a Harley 6 Speed.


The fuel price is an essential factor that you need to consider when you own a vehicle. That’s why you have to choose those transmission oils that provide high-quality performance and are also pretty reasonable in price.


The more compatible the oil is with your vehicle, the more performance you’ll have while riding your Harley.

People have been known to buy high-quality transmission oil without testing compatibility, only to have problems with the engine’s performance later.

As a result, always double-check compatibility before selecting a transmission oil for your car.

Frequently Asked Questions

If you still have any questions about the best transmission oil for Harley 6 speed then go through the below FAQ section. Here you’ll find most of the answers to these queries that people frequently asked.

Are synthetic transmission oils superior to natural transmission oils?

Synthetic transmission oils are certainly better than natural ones in many aspects. The first reason is synthetic oils can lubricate the engine more than natural ones. Moreover, synthetic ones get along more with a motorcycle engine.

Can I use 75w90 in my Harley transmission?

You are allowed to use a 75W90 in a Harley trans, but the performance won’t be the best. The oil will run your bike well, but there will be times when the overall performance may not be the way you wanted. So, you can rather pick a 20W50 oil instead to get a satisfying performance.

How frequently does the transmission oil of the Harley 6-speed engine need to be changed?

The transmission oil’s changing frequency depends on how many times you have started the vehicle. Experts usually recommend changing the oil to at least at 1,000 miles, then after every 10,000 miles. In this way, your Harley engine would remain in good shape.

Is it possible that using synthetic transmission oil may void your warranty?

Not all synthetic transmission oil would invalidate your warranty, but the actual answer depends on the brand. Some synthetic oils can invalidate the motorcycle warranty if the brand’s specifications are not satisfactory. That’s why you must check the brand specifications from the manufacturers before buying a transmission oil.

Bottom Line

We hope, you’ve got enough information to get yourself the best transmission oil for Harley 6 speed after reading this guide. All of the transmission oils listed here are of high quality. However, according to our experts, Spectro Heavy Duty is one of the top-rated oils that you can choose.

This transmission oil is an ideal choice for its overall performance and smooth ride that it offers to the riders. Moreover, it does even provide protection to your Harley engine by preventing it from wear and tear.

Ryan Walker

Ryan Walker

Hi, I'm Ryan Walker, the chief editor and the founder of this site, Motoable. I’m a bike rider, and I’ve been riding motorbikes for almost thirty-five years. I worked for a renowned motorbike accessories manufacturing company for twelve years as a quality in charge.Later, I start my own business where I sell different bike accessories and safety gear for motorbikes. I created this site Motoable to share my experience with other bikers who are new to this field and don’t have adequate knowledge about motorbikes and their accessories.

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