Harley 6 Speed Transmission Oil Capacity: Shift Gears Smoothly

Although most Harley 6-speed gearboxes have an approximate transmission oil capacity of 32 oz, it varies depending upon the model year. Knowing your Harley’s exact transmission oil capacity is crucial for regular maintenance.

It is because overfilling and underfilling the transmission oil could lead to hard shifting and eventually wearing up your gearbox. Thus, let us dig into knowing the approximate requirement of transmission oil capacities for all available models of Harley 6-speed transmission.

Harley 6 Speed Transmission Oil Capacity

There are lots of variations of Harley Davidson motorcycles with the 6-speed transmission out there in the marketplace. 

You can use the following chart to understand the 6-speed transmission oil capacity for a specific series launched by Harley Davidson.

Harley Davidson ModelsOil Capacity (US Standard Unit)Oil Capacity (Metric Unit)
Trike Models1 Quart/32 oz0.95 mL
Softail Models (After 2007)28oz to 1 Quart/32 oz0.83-0.95 mL
Touring models (After 2007)1 Quart/32 oz0.95 mL
Street Models1 Quart/32 oz0.95 mL
Dyna Models (after 2006)28oz to 1 Quart/32 oz0.83-0.95 mL
Police Models28 oz0.83 mL
FLHTCUTGSE Models28 oz0.83 mL
FLTRUSE Models1 Quart/32 oz0.95 mL

As you can see the most 6-speed transmission of Harley uses up to 950mL of lubricating fluid. 

All these transmission systems come in collaboration with twin-cam 96 and 103 engines. 

Besides the Milwaukee 8 engines also use a similar gearbox with the exact requirement of transmission oils.

However, there are some exceptions as well. The Police model uses the Milwaukee-8 107 CU engine with 6-speed transmission but uses around 28 ounces of transmission oil which is equivalent to 830mL of fluid. 

Most early models of the Softail and Dyna series also used 28 oz of transmission in their 6-speed transmission system.

Read Also: Harley Fork Oil Capacity Chart [A Quick And Easy Guide]

Types Of Oil For Harley 6 Speed Transmission 

Officially, Harley recommends using fully synthetic 80w140 grade transmission oil for the 6-speed transmission system. 

You can use other grade oils, such as 70W90 or 75W140, if you are residing in a hot region.

A lot of aftermarket transmission oils are available in the marketplace. Here are some recommended 6-speed transmission oils for Harley 6-speed V-twin transmission systems.

Oil NameOil Type
Harley-Davidson OEM SYN-3OEM (Factory Fill)
Spectro RHDPG6 Heavy Duty Platinum Full Synthetic 6-Speed Transmission OilFull Synthetic
Amsoil Synthetic Six-speed V-Twin Transmission Fluid (MVT)Synthetic
Red Line 90226 Six-speed V-Twin Transmission OilSynthetic
Mobil DELVAC V-Twin Transmission OilSynthetic
Bel-Ray 96920-BT1 Big Twin Transmission OilMineral
Lucas Oil Synthetic 20W50 Transmission OilSynthetic
Castrol Power RS V-Twin Synthetic 20W50 Transmission oIlSynthetic
Quicksilver 20W50 Synthetic Motorcycle OilSynthetic

Read Also: Who Makes Harley Davidson Oil? Things You Mightn’t Know!

How to Change Harley Transmission Oil?

Follow this step-by-step walkthrough to change the transmission oil and save a lot of money from being paid to the dealership or mechanic.

Gather Necessary Tools

These are some mandatory tools you need before proceeding to change the transmission oil.

  • A drain pan
  • A ⅝ inches socket with a socket wrench 
  • 3/8in ball end Allen(depending on your bike’s drain plug), 
  • New gasket or O-ring for the drain plug, 
  • Funnel
  • Transmission oil for your specific Harley Davidson model.

Initial Preparation

Transmission oil is very thick and sticky at lower temperatures. Hence, it is better to ride your Harley for a while so that the gearbox reaches the optimum operating temperature. 

It makes draining the transmission oil very easy and quick. Secondly, perform the transmission oil change while parking your Harley on the kickstand. 

It is better to refer to your user’s manual to know how to keep the bike parked beforehand.

Read Also: How To Check Primary Oil On Harley Davidson? [6 Easy Steps]

Draining The Oil

Normally, you will find the drain plug near the base of the transmission case. To collect the used oil, place the drain pan beneath the drain plug. Use the socket wrench to loosen up the drain plug. 

After that, you can use your hand to remove the drain plug so that it doesn’t fall into the oil. 

Let all the used oil drip into the pan. Clean the drain plug and check for any physical damage, especially the O-ring to avoid oil leakage. 

Insert a new O-ring inside the drain plug and reinstall it using a torque wrench with 14-21 ft/lbs torque settings.

Pouring New Transmission Oil

Now according to your Harley model and specifications pour the new transmission oil through the funnel. It is advised to first pour 28 oz of oil and further refill it till it hits the level mark.

Use the dipstick to know the oil level inside the chamber. It should mark the F (Full). Avoid overfilling transmission oil as you may encounter oil leakage. 

Lastly, reinstall the transmission oil cap. Do not overtighten the cap as it may break the seal of the gasket or O-ring.

Read Also: Harley Davidson Twin Cam 88 Oil Capacity [An On-Point Guide!]

Importance Of Maintaining Transmission 6 Speed Oil Level

Transmission oil is used to minimize the friction coefficient between the metallic gears, bearing, and other internal components. 

Additionally, it assists in cooling the transmission by absorbing heat and cleaning out impurities.

A sufficient oil level ensures quick gear shifting, stops excessive temperature buildup, and prevents early component damage. 

Overfilling can result in foaming, decreased lubrication efficiency, and leaking.

On the other hand, not enough oil can cause higher friction, overheating, and probable transmission damage. 

You can ensure the proper operation of the transmission and the extension of its life by routinely inspecting and maintaining the correct transmission fluid level.


Check out these answered questions from Harley enthusiasts to know more about transmission oil-related queries.

How Do You Check The Transmission Fluid On A 6-Speed Harley?

On the transmission case, locate the fill plug or dipstick for the transmission oil. Remove the plug/dipstick using a ball-Allen, clean it off, reinstall it, and check the oil level. Ensure that the motorcycle is upright and the engine is warmed up.

Is Harley Transmission Oil The Same As Engine Oil?

Engine oil and transmission oil on Harleys is not identical. They serve various functions and have different formulas. Engine oil is created for the engine with a different viscosity oil grade, whereas transmission oil has been designed for the transmission system.

What Viscosity Is Harley Transmission Oil?

Harley transmission oil grade varies depending upon the choice of users. Officially Harley recommends 80w140 grade oil. However, 70w140 and 75w140 grade oils can also be used.

What Is The Best Transmission Oil For My Harley Davidson?

The Harley Davidson Heavy Synthetic 80w140 Gear oil and Amsoil Synthetic V-twin Transmission oils are the best-suited oil for Harley motorcycles. Besides, Redline, Spectro can also be used.

Final Words

Hopefully the information was helpful. Harley has both 5-speed and 6-speed transmission systems in their arsenal. 

You must know the exact amount of transmission oil to be poured into your Harley bike. Since it varies with the generation and models it is better to be updated.

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