8 Best Transmission Fluid For Harley 6 Speed Reviewed in 2022

Whether you are a beginner or professional biker, your motorcycle’s transmission can directly affect the riding experience. And when it comes to Harley Davidson, the perfect transmission fluid is a must for maximum gear control.

Since its debut in 2007, Harley 6-speed transmission has been a popular term among Harley riders. Some feel a slight drag on the 5th gear or complain about the irritating noise at highway speed. To overcome these inconveniences, you need the best transmission fluid for Harley 6 speed.

Most of the time, the transmission fluid is specific for different bike models. So it’s easy to change or flush the oil only if you know what your bike needs. Imagine all the trips to auto-repair shops you can avoid!

Here we’ve reviewed some of the best transmission oil for Harley 6 speed. Also, included a buying guide, so you can choose on your own. So, let’s give it a go.

Editor’s Choice

Red Line Big Twin 20w50 Power Pack

9.7
Red Line Big Twin 20w50 Power Pack
  • Brand: Red Line
  • Viscosity: 20w-50
  • Volume: 7 Quarts
  • Weight: ‎15.6 pounds
  • Dimensions: ‎16.5 x 8.5 x 9.5 in
Best Single-quart Oil

Red Line V-Twin Transmission Oil

9.5
Red Line V-Twin Transmission Oil
  • Manufacturer: ‎Red Line
  • Brand: ‎Red Line
  • Model: ‎42804
  • Weight: ‎1.7 pounds
  • Dimensions: ‎16 x 12 x 10 in
Best for Twin Cam

Maxima Twin Cam Synthetic 20W-50 Complete Oil Kit

9.1
Maxima Twin Cam Synthetic 20W-50 Complete Oil Kit
  • Viscosity: 20w-50
  • Brand: Maxima
  • Volume: 192 Fluid Ounces
  • Weight: ‎14 pounds
  • Dimensions: ‎16.5 x 6 x 12.5 in

Do Motorcycles Need Transmission Fluid?

Transmission fluid lubricates all the components inside a gearbox to ensure smooth gear shifting, keep it cool, and reduce wear. But, how does it work?

A transmission efficiently converts a rotating power source, such as an engine, to another device. It transmits the combustion engine power to the wheels and regulates motorcycles’ speed, torque, and RPM (rotations per minute).

The transmission system, often called the gearbox, includes clutch, gears, shifts, final-drive, and a dozen other parts.

One other essential part of a motorcycle transmission is the transmission fluid that lubricates all the components inside the gearbox. These components tend to wear off over time, which directly affects a motorcycle’s speed and efficiency.

Transmission fluid prevents the damage as a lubricant and cleans the metal surfaces inside the gearbox. It also works as a coolant during high speed and long hauls.

In automatic transmissions, like electric motorcycles, transmission fluid provides enough friction and hydraulic pressure to make the transmission work.

Although modern-day bikes feature automatic transmission, classic motorcycles like the Harley cruisers and touring bikes still use a manual transmission.

Apart from their structural differences, both automatic and manual motorcycles need transmission fluid nonetheless.

What Kind Of Transmission Fuel Can Be Used In A Harley 6?

There are mainly two kinds of transmission fluids that go with Harley 6-speed bikes: natural oil and synthetic oil.

Natural Oil

Natural oil (from crude oil) is a petroleum-based liquid hydrocarbon. This type of transmission fluid is highly soluble with additives and way inexpensive than its counterpart.

Crude oil is compatible with a vast range of vehicles, but it does not perform well in high temperatures. Since natural oil is highly soluble, it tends to break down quickly and requires frequent changing.

Synthetic Oil

Synthetic oil is a modified petroleum compound and is currently the best Harley Davidson transmission oil type. Firstly, synthetic oil offers more mileage than standard oil, so you can run thousands of miles before the tranny oil requires a change.

Secondly, with the proper additives, synthetic oil effectively lubricates the gears to reduce noise and wear. Hence it provides better gear shifting than natural oil.

Last but not least, this oil type is far superior in extreme weather conditions. Unlike crude oil, you will get flawless transmission during both cold and hot weather.

The only drawback of synthetic transmission oil is, it’s more expensive than standard natural oil. But it’s always a good decision to pick performance over price even though you’ll have to change it less often.

What Are The Best Transmission Fluids for Harley 6 speed?

Table of Content:

In this section, you can see the different topics we covered in this article and all the different products we reviewed to navigate easier.

Comparison Chart:

In a hurry? See this comparison chart to take a quick look at the transmission oils we’ve covered:

Image Product Technical Spec Price
Editor’s Choice

Red Line Big Twin 20w50 Power Pack

Red Line Big Twin 20w50 Power Pack
  • Brand: Red Line
  • Viscosity: 20w-50
  • Volume: 7 Quarts
  • Weight: ‎15.6 pounds
  • Dimensions: ‎16.5 x 8.5 x 9.5 in
Check Price
Best Overall

Spectro Oil Heavy Duty Platinum Full Synthetic Trans Lube

Spectro Oil Heavy Duty Platinum Full Synthetic Trans Lube
  • Brand: Spectro Oil
  • Model: ‎R.HDPG6
  • Volume: 32 Fluid Ounces
  • Weight: 2.08 Pounds
  • Dimensions: ‎4 x 2.5 x 8.95 in
Check Price
Best Value for Money

Mobil-Delvac Synthetic Transmission Fluid 50 (Pack of 4)

Mobil-Delvac Synthetic Transmission Fluid 50 (Pack of 4)
  • Manufacturer: ‎Mobil
  • Brand: ‎Mobil
  • Model: ‎112812-4PK
  • Weight: ‎32 pounds
  • Dimensions: ‎16.9 x 12.1 x 10 in
Check Price
Best Single-quart Oil

Red Line V-Twin Transmission Oil

Red Line V-Twin Transmission Oil
  • Manufacturer: ‎Red Line
  • Brand: ‎Red Line
  • Model: ‎42804
  • Weight: ‎1.7 pounds
  • Dimensions: ‎16 x 12 x 10 in
Check Price
Best Budget

Bel-Ray VTwin Primary Chaincase Lubricant

Bel-Ray VTwin Primary Chaincase Lubricant
  • Manufacturer: ‎BEL-RAY
  • Brand: ‎Bel-Ray
  • Model Number: ‎3604-0003
  • Weight: ‎2 pounds
  • Dimensions: ‎8.5 x 5 x 2.5 in
Check Price
Best ATF

RAVENOL ATF 8 HP 8-Speed & 6-Speed Transmissions Oil

RAVENOL ATF 8 HP 8-Speed & 6-Speed Transmissions Oil
  • Manufacturer: ‎RAVENOL
  • Brand: ‎RAVENOL
  • Model Number: ‎J1D2113
  • Weight: ‎2.05 pounds
  • Dimensions: ‎11.44 x 6.91 x 4.65 in
Check Price
Best Cost-effective Pack

ZF Life Guard Fluid 8 (7 Liter)

ZF Life Guard Fluid 8 (7 Liter)
  • Manufacturer: ‎ZF PARTS
  • Brand: ‎ZF
  • Fitment Type: Direct Replacement
  • Weight: ‎14.62 pounds
  • Dimensions: ‎17.4 x 11.6 x 8.6 in
Check Price
Best for Twin Cam

Maxima Twin Cam Synthetic 20W-50 Complete Oil Kit

Maxima Twin Cam Synthetic 20W-50 Complete Oil Kit
  • Viscosity: 20w-50
  • Brand: Maxima
  • Volume: 192 Fluid Ounces
  • Weight: ‎14 pounds
  • Dimensions: ‎16.5 x 6 x 12.5 in
Check Price

8 Best Transmission Fluid For Harley 6 Speed Reviews 2022

Best Transmission Fluid For Harley 6 Speed

1. Editor’s Choice: Red Line Big Twin 20w50 Power Pack

Red Line Big Twin 20w50 Power Pack

What’s better than a single quart tranny oil? The Red Line Big Twin Powerpack is a complete motorcycle kit that meets all your lubrication demands.

High Viscosity

Synthetic oil performs better in hot temperatures. And that’s where the Red Line V-twin Powerpack comes in handy. With its 20W50 oil viscosity level, it’s perfect for both cold and hot conditions. As all the oil included features the same oil grade, this powerpack efficiently regulates engine temperature and reduces wear.

Shockproof Additives

This oil package kit comes with 1 quart of pink transmission oil with shockproof additives. Shockproof is a friction modifier specially designed to reduce the friction between gears and clutches. As a result, you will get the quietest motor performance and gear shifts from your Harley 6-speed.

Noiseless High Efficiency

This Red Line oil package is one of the best transmission fluids for Harley because of how cost-effective it is. You will get a complete oil set for a wide range of Harley motorbikes as an economical pack. Not only does it enhance the performance of your V-twin engine, but it also ensures less noise, smooth gear shifting, and efficient fuel economy.

Wide Bike Model Compatibility

The Red Line 20W50 powerpack is compatible with Evolution, Milwaukee-Eight, and Harley Davidson 96-inch twin-cam engines. So, that includes all the H-D motorcycles from 2007-up like Dyna, Touring bikes, etc.

Full package with Extras

As a complete kit, it comes with a primary chaincase oil. However, you may need to purchase one extra bottle of that oil for large twin cam engines (38 oz wet; 45 oz dry), as the featured kit is mainly compatible with V-twin’s 32 oz capacity. Red Line also tested all the included fluids to meet a complete oil change.

Technical Information

  • Package Weight: 15.6 pounds
  • Fluid Type: Synthetic Oil
  • Viscosity: 20W-50
  • Fluid Amount: 1 quart
  • Package Includes: ‎V-Twin Transmission Oil, Chain Case Oil, Fuel Injection Cleaner, Funnel, Sicker Kit, Hat
Why Do We Love It?
  • Low oil grade is compatible with a range of temperatures
  • Comes with all necessary fluids necessary for a motorcycle
  • Shockproof technology reduces wear and noise significantly
  • Compatible with all recent H-D motorcycles featuring twin-cam engines
  • Pink color transmission oil is easier to keep track of
What Should Improve?
  • Requires an additional chaincase oil purchase for large V-twin

Summary

The Red Line Big Twin Powerpack is the most cost-effective and well-performing oil kit for beginners and hardcore bikers alike. So, hit the extra mileage with this H-D certified easy-to-use complete lubricant kit.

2. Best Overall: Spectro Oil Platinum Full Synthetic Trans Lube

Spectro Oil Heavy Duty Platinum Full Synthetic Trans Lube

The Spectro Platinum is a full synthetic trans oil that goes with a range of motorcycles, especially V-twin. With its GL-5 rating and 75W140 oil grade, it is born for Harley 6-speed riders.

Proper Viscosity

Being especially built for hot engine conditions, this tranny oil has an oil grade of 75W140. So you don’t have to worry about jammed transmission or clunks on long hauls. Due to its high viscosity, heavier load, and extreme heat during long summer days won’t affect the oil in anyways.

High end G4 Additives

Spectro Platinum is a top choice if you are looking for anti-wear protection and higher film strength. This particular oil features the G4 technology, a unique additive that reduces the clutch drag and extends gear life.

Smooth Shifting

6-speed transmissions tend to make an irritating noise in 5th gear. Fortunately, the Spectro Platinum reduces that noise drastically and provides the smoothest shifting any Harley rider can ask for. In fact, Spectro specifically designed this oil to cure this noisy transmission in helical and straight-cut gears.

High-Temp Efficiency

Thick transmission oils sometimes wear off the internal part, and you may notice small metal pieces in the dipstick. But not with the Spectro Platinum 75W140. Despite its high density, it provides additional protection to reduce wear. Besides, longer rides are more cost-effective as higher loads and temperature don’t affect the oil.

Technical Information

  • Package Weight: 2.08 pounds
  • Fluid Type: Synthetic Oil
  • Viscosity: 75W-140
  • Fluid Amount: 1 Quart
  • Package Includes: 1x Spectro Platinum Transmission Oil
Why Do We Love It?
  • Smooth and quiet transmission on 5th gear
  • Withstands high temperature and workloads
  • G4 technology protects and increases gear life
  • Additives Increase film strength
What Should Improve?
  • A bit costlier than other single quarts

Summary

If that clunking noise during gear change irritates you, check out this transmission oil. It is one of the best transmission fluids for Harley 6-speed that also ensures smooth operation and withstand high pressure.

3. Best Value for Money: Mobil-Delvac Synthetic Transmission Fluid 50 (Pack of 4)

Mobil-Delvac Synthetic Transmission Fluid 50 (Pack of 4)

The reason why we listed this large 4-pack transmission fluid is simple- it’s worth it. The Delvac synthetic transmission oil ensures excellent performance and outstanding protection for many motor vehicles, including Harley 6-speed.

High Viscosity Level

It is an SAE 50W90 gear lubricant, meaning it can withstand high temperatures at ease. Due to its high viscosity level, it provides excellent shear stability and film strength. In contrast, it can also perform effectively at below-freezing temperatures.

Corrosion Free Additives

Mobil formulated this transmission oil to enhance gear performance and oxidation stability under any condition. Also, the additives will provide exceptional wear protection, corrosion control, and protection from deposit formation. As you can see, the Delvac synthetic trans oil is capable of protecting your Harley transmission from any internal damage.

Extra Mileage

If you are a Harley biker, you know how annoying it can be to change the tranny fluid after a few thousand miles. But this Mobil oil will help you hit that extra mileage as a manual transmission-specific fluid. Due to its extensive protective features, you don’t have to change the oil that often. And even if you have to change, you’ll always have spare bottles close by as this is a pack of four.

GL-4 Gear Performance

This oil prevents any damage to your 6-speed transmission and effectively protects the thermal process. Besides, this fluid meets vital industry standards for GL-1 through GL-4 gear protection, in addition to some other API standards. With Mobil, you’ll always have the assurance for top-notch performance.

Technical Information

  • Package Weight: 32 pounds
  • Fluid Type: Synthetic Oil
  • Viscosity: SAE 50
  • Fluid Amount: 1 gallon
  • Package Includes: 4 x Mobil-Delvac Synthetic Transmission Fluid
Why Do We Love It?
  • Excellent thermal and oxidation stability
  • Anti-wear and anti-corrosion additives
  • Superior protection against deposit formation
  • Works perfectly in different thermal conditions
  • Goes with Harley, trucks, cars, and other motor vehicles
What Should Improve?
  • More expensive than other products

Summary

If you are looking for proven transmission oil that can give you the best value for money, then Mobil is your best bet. It works extremely well in hot weather conditions and minimizes the chances of damage through additives.

4. Best Single-quart Oil: Red Line V-Twin Transmission Oil

Red Line V-Twin Transmission Oil

The Red Line V-twin trans oil is one of the best transmission fluids for Harley 6-speed due to its noise reduction and high performance. It also features the necessary additives to enhance gear mobility, Harley touring bikes, and sports bikes alike.

Friction Modifiers

Friction modifiers are a type of anti-wear additive that minimizes sliding and rolling between the gears. These additives modify the lubricant friction to prevent oxidation and metal surface breakdown. Often referred to as EP additives, these modifiers can thrive under extreme pressure (EP) and works to increase fuel economy.

Shockproof

Another additive that you’ll get is the result of “shockproof” technology, and it mainly works to reduce gear noise. Shockproof transmission oil for Harley bikes offers low drag and dramatically reduces shifting clunk.

Performance

Changing gears is an essential part of riding, especially in sports bikes, and you’ll need the change to be flawless. This Red Line synthetic oil ensures that with the help of different additives and excellent viscosity characteristics. Moreover, it works as a coolant and reduces the risks of damaging your bike’s engine.

Compatibility

Red Line V-twin Synthetic oil is Harley Davidson certified so that you can use it without a doubt. Also, this fluid is compatible with four-stroke motocross and ATV sport bikes as well.

Technical Information

  • Package Weight: 1.7 pounds
  • Fluid Type: Synthetic Oil
  • Fluid Amount: 1 quart
  • Additives: Shockproof Technology
  • Package Includes: 1 x red Line V-twin Transmission Oil
Why Do We Love It?
  • Shockproof technology minimizes irritating gear noise.
  • Works in extreme temperature and heavy loads
  • Friction modifiers ensure flawless transmission
  • Compatible with the latest high-revving Harley Twin cams
  • Pink color let the user quickly locate leaks and wear
What Should Improve?
  • Some users find it difficult to distinguish the color of old oil.

Summary

Red Line needs no introduction into the motorcycle world, and this lubricant is one of their best. If low noise, high workloads, and flawless transmission is what you need, then this tranny oil got you covered.

5. Best Budget: Bel-Ray VTwin Primary Chaincase Lubricant

Bel-Ray VTwin Primary Chaincase Lubricant

Bel-Ray specially formulated this lubricant for the primary chaincase that all V-twin motorcycles use. However, this petroleum-based lubricant has shown decent efficiency for older Harley 6-speed transmissions that still use natural oil.

Low-Temperature Viscosity

Petroleum-based transmission oils tend to have lower thickness than synthetic oil, and this Bel-Ray product is no different. Lower viscosity works well in low temperatures and can withstand high pressure. This fluid also reduces wear on the primary chain and clutch, especially if using a Harley hydraulic clutch.

Longer Gear Lifespan

Unlike synthetic oil, this natural oil doesn’t feature that many additives. But it does ensure a longer gear lifespan with anti-wear technology. Furthermore, it allows smooth clutch engagement by preventing slipping and chatter. Finally, you get superior oxidation protection that works well in low to medium temperatures.

Red Tinted Easy Tracking

This natural oil is dyed with red color, like all Red Line products, so that the user can spot leaks easily. Again, with a red tint, it’s easier to determine how burned out the oil is.

Technical Information

  • Package Weight: 2 pounds
  • Fluid Type: Natural Oil
  • Fluid Amount: 1 liter
  • Compatibility: V-twin Chaincase and Transmission
  • Package Includes: 1 x Bel-Ray V-Twin Chaincase Lubricant
Why Do We Love It?
  • Reduces wear on the primary chain and clutch.
  • Allows smoother clutch engagement/disengagement.
  • Withstands low temperature and high pressures.
  • Serve multiple purposes (primary chain and transmission)
What Should Improve?
  • Natural oil is not ideal for recent Harley 6-speed bikes.

6. Best ATF: RAVENOL ATF 8 HP 8-Speed & 6-Speed Transmissions Oil

RAVENOL ATF 8 HP 8-Speed & 6-Speed Transmissions Oil

RAVENOL is a German oil brand famous for making high-quality car engine oils and Harley motorcycles. This particular ATF (auto-transmission fluid) is an excellent choice for both 8-speed and 6-speed motor vehicles.

High Viscosity index

RAVENOL ATF has a high viscosity index that is highly effective in both cold and severe hot conditions. It is designed for 8-speed motor cars, it can withstand higher temperatures better than many transmission oils. An ATF also works as a coolant to reduce the temperature of gearbox components, and this one is no different. As a result, both the engine and transmission get better longevity and work efficiently.

Friction Modifier Additives

Moving on to the additives, this ATF features friction modifiers that reduce sliding and rolling. Another function this anti-wear technology serves is to prevent corrosion of metal surfaces inside a gearbox. This transmission fluid also cleanses off the debris and gunk. Moreover, you get decent oxidation and thermal stability with this transmission fluid.

Hot/Cold weather

When a company manufacture oil for brands such as BMW, Honda, Audi, and Harley Davidson, there’s should be no question regarding quality. As such, this RAVENOL ATF has made its way to the top with its compatibility with both 6-speed and 8-speed vehicles. It’s perfect for both cold and hot weather conditions and requires low maintenance.

Exception

RAVENOL recommends that users should check product info and OEM part number before purchase. This is due to California Proposition 65 warning and vehicle compatibility standards.

Technical Information

  • Package Weight: 2.05 pounds
  • Fluid Type: ATF Synthetic Oil
  • Compatibility: 8-speed and 6-speed Vehicles
  • Fluid Amount: 1 liter
  • Package Includes: 1 x RAVENOL ATF – 8 HP
Why Do We Love It?
  • Keep the gearbox clean from debris and gunk
  • Work efficiently in both 6-speed and 8-speed vehicles
  • It works as a coolant
  • Features friction modifier to reduce wear
What Should Improve?
  • May need prior knowledge for fluid change or flush.

Summary

Over time, the gearbox starts to wear off and lose efficiency. However, with this heavy-duty automatic transmission oil, you won’t have to worry about your Harley transmission.

7. Best Cost-effective Pack: ZF Life Guard Fluid 8 (7 Liter)

ZF Life Guard Fluid 8 (7 Liter)

Similar to the Delvac synthetic oil, this ZF Life Guard Fluid 8 is a pack of seven 1-liter transmission fluids. It’s not specific for Harley, but still one the best transmission fluid for Harley 6-speed per the user demand.

Viscosity

This ZF product is special for a 6-speed gearbox, like those in 2007-up Harley Davidson bikes. It doesn’t always depend on a specific temperature to provide the most efficiency. Instead, it performs exceptionally both in cold and hot weather conditions alike.

As a result, this transmission fluid is also well-known for its application in VW, Mercedes, BMW, and many other car brands.

Quieter Performance

As you have already guessed, this tranny fluid significantly improves gear usability. You get a smoother and quieter shifting due to its brilliant performance.

Cost-effective

One other issue many riders face is that most high-performing Harley transmission oils are costly. With this ZF product, you have a very economical choice as this is a pack of 7-liter transmission fluid. Not only can you change your old tranny fluid, but you’ll still have plenty left to go around other vehicles in your possession. But first, make sure this ZF Life Guard is compatible with those vehicles.

Less Maintenance

There’s a small drawback with this tranny oil, and that is, it may take the prior experience to change the fluid. This oil requires two successive flushes during transmission oil flush and at a specific temperature.

Technical Information

  • Package Weight: 14.62 pounds
  • Fluid Type: Synthetic Oil
  • Fluid Amount: & liters
  • Package Includes: 7 x ZF Life Guard Fluid 8
Why Do We Love It?
  • Cost-effective choice for Harley 6-speed
  • Compatible with a wide range of vehicles
  • Works at different weather conditions
  • Improves transmission longevity
What Should Improve?
  • Fluid flush is a bit tricky.

Summary

This transmission oil is a cost-effective pack for anyone looking for oil for different types of vehicles alongside the Harley Davidson 6 speed.

8. Best for Twin Cam: Maxima Twin Cam Synthetic 20W-50 Complete Oil Kit

Maxima Twin Cam Synthetic 20W-50 Complete Oil Kit

Lastly, we have another complete Harley oil kit- the Maxima Racing Oils Twin Cam oil. It’s one of the best transmission fluids for Harley 6-speed and fits all Twin Cam engines from 1999 to date.

80W-90 Viscosity

As it features 80W-90 viscosity, you no longer have to worry about a burning hot engine during long rides. However, Maxima actually cut short the synthetic oil and offered natural oil as tranny fluid instead.

So, many riders would argue how this may affect the performance during low temperatures. But you don’t have to worry about high temperature and heavy load due to its higher viscosity index.

Smooth-shifting

This mineral-based oil has a high film strength and efficiently reduces shock, wear, and metal surface breakdown. Smooth-shifting is also an assurance due to other additives.

Decent Performance

Apart from its high heat tolerance, this fluid possesses decent cooling ability as well. Natural oil is comparably less fuel-efficient. But the Maxima transmission oil performs well to deliver additional mileage without any hassle.

Compatibility

As we already mentioned, this fluid is compatible with all V-twin engines from 1999 to date. Furthermore, you can use this oil kit as a 4th and 5th gear fluid in older Harley Davidson bikes.

Technical Information

  • Package Weight: 14 pounds
  • Fluid Type: Natural Oil (Transmission Fluid)
  • Viscosity: 80W-90
  • Fluid Amount: 192 ounces
  • Package Includes: 4 x V-Twin Synthetic Engine Oil, 1 x V-Twin Mineral Transmission Oil, & 1 x Chrome 171C Oil Filter
Why Do We Love It?
  • Compatible with 4, 5, and 6-speed gearbox
  • Works in high-pressure conditions
  • Cools down the engines effectively
  • Features detergents to keep the gearbox clean
What Should Improve?
  • Need to check if your bike supports natural transmission oil

Summary

Another oil pack that fits all twin-cam Harley motors from 1999 to date. Got yourself a Harley classic? Then the Maxima V-twin oil kit is the way to go!

How To Choose The Best Transmission Fluid For Harley 6 Speed?

Choosing the best transmission fluid for Harley 6-speed can be a difficult task. Different Harley Davidson models require different types of tranny oil. So, you should go through all the necessary considerations first.

How To Choose The Best Transmission Fluid For Harley 6 Speed?

Viscosity

Viscosity refers to the thickness of the transmission fluid. With low viscosity, the fluid runs more freely and faster. On the other hand, high viscous oil tends to deliver better surface tension.

Viscosity level is determined using two different numbers. The first one indicates how viscous the oil is in a cold engine. That’s why the number comes with the letter “W” at its end, referring to winter. The second number determines the oil flow at higher temperature levels.

For example, a 10W-40 viscosity means that the oil has an index of 10 for cold and up to 40 for hot working conditions. The viscosity is a very vital factor for transmission fluid as wrong viscosity can harm the gearbox components.

Types

We already talked about two different types of tranny fluid for Harley 6. Most recent Harley models are compatible with synthetic oil. But the wrong kind of fluid may void your warranty. So, you should always check the user manual to be sure what type of oil your bike needs.

Additives

Additives are the next most important thing you need to consider as they serve multiple purposes. For instance, additives keep the gearbox clean by removing metallic parts, debris, and acid. They also keep the transmission cool and work as friction modifiers. As different metallic parts inside a transmission function differently, you should be careful to choose the oil with proper additives.

Compatibility

A common issue with motorbikes is that the engine starts to leak. This is due to using the wrong oil that isn’t suitable for a particular engine. And that’s why you should always check your bike’s user manual or the transmission fluid’s compatibility list to ensure you are using the right one. The wrong type of transmission oil may damage your bike components and void the warranty.

Frequently Asked Questions

With all the information flying around the web, it’s only natural to get confused. So, here are some of the FAQs we have answered for your convenience.

When should I change the transmission oil in my Harley?

A Harley Davidson bike runs, and the oil needs to be changed at every 10,000 miles and trans fluid at 20,000 miles. But it is safe to change at every 5,000 miles.

How much transmission fluid does a Harley Davidson 6-speed take?

The amount and type of fluid to be used are variable, and it’s used in the engine, chain card, and the tranny. For the gearbox, a quarter of fluid will do the trick.

Is synthetic oil better than standard oil?

Yes. The use of synthetic oil requires less oil change, and it also decreases the transmission noise compared to standard oil. It is also more weather and heat-resistant and features more additives.

Can I use ATF in my Harley primary?

It depends on the model and your preference. Although many Harley users said that they’re satisfied for years with the use of ATF, a thicker oil provides better metal-to-metal wear protection in the primary.

Are primary oil and transmission fluid the same?

No. The motor oil used for engines is different from ATF because it can differentiate contaminants when burning fuel. Transmission fluid needs to be thinner in order to provide smooth gear shifting.

Final Thoughts

Transmission fluid reduces wear and noise and enhances riding performance alongside smooth gear change. If the fluid is poorly maintained, it will do more harm than good. So, you need to change or flush your Harley’s tranny oil accordingly.

We would suggest the Red Line Twin Cam Powerpack as our editorial choice for the best transmission fluid for Harley 6 speed. This pink tranny fluid features 20W-50 oil grade and shockproof technology to reduce wear in any weather conditions. Besides, it’s a complete oil kit for all recent 6-speed Harley motorcycles. Finally, you can shift between different gears smoothly and quietly with this transmission fluid.

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