AMSOIL 100% Synthetic V-Twin Transmission Fluid

Product overview

A Big Twin gearbox runs its own oil, separate from the engine and the primary chaincase, and it takes a heavier fluid than either one. AMSOIL Synthetic V-Twin Transmission Fluid runs 20.7 cSt at 100°C to keep a film on straight-cut gears carrying full engine torque.

It is engineered for Harley-Davidson, Triumph, and pre-2013 Indian motorcycles, and it is Warranty Secure, so running it keeps the factory warranty intact.

What the formula does

• Precise friction control delivers smooth shifts and helps quiet transmission whine.
• A durable oil film on the gears and bearings dampens the loud thunk on a shift and reduces gear noise.
• Extreme-pressure additives and high film strength protect against shock loading and gear wear.

Where this fluid fits

Engineered for use in:

• Harley-Davidson motorcycles
• Triumph motorcycles
• Pre-2013 Indian motorcycles

Which sump on a V-twin this fluid fills

A Big Twin drivetrain keeps the engine, transmission, and primary chaincase in three separate compartments, and each one holds its own oil. AMSOIL Synthetic V-Twin Transmission Fluid belongs in the middle compartment, the gearbox, and the fitment test is simple: it goes in any V-twin transmission that does not share a sump with the engine, including the gearboxes found on Harley-Davidson, Triumph, and pre-2013 Indian motorcycles.

That distinction matters at the parts counter, because a bottle labeled for the engine or for the primary chaincase is not a substitute for the gearbox fill. A dirt bike with its own separate gearbox sump needs a different formula again, which is AMSOIL Synthetic Dirt Bike Transmission Fluid.

What gear teeth do to a transmission fluid under load

Straight-cut gears carrying full engine torque generate extreme pressure at every tooth contact, and that pressure will break a weaker transmission fluid down and let it thin out until it no longer protects the parts. Synthetic V-Twin Transmission Fluid is built to hold its thickness through that loading and to stand up to extreme heat while it does.

Its robust molecules supply the film strength that absorbs shock loading, the kind that arrives when a gear engages hard, and extreme-pressure additives give the gears and bearings an additional measure of wear protection. Shift quality comes out of the same package, since finely tuned viscosity and frictional properties are what let a rider move cleanly through the gears without a missed shift.

Cold storage and the first miles of the season

A motorcycle that sits through winter starts its first ride of the year with cold, thick oil in every compartment. Synthetic V-Twin Transmission Fluid has a pour point of -40°C (-40°F), so it is still able to flow at temperatures well below anything a rider is likely to start a bike in.

A viscosity index of 127 describes how steadily the fluid holds its thickness across that swing, from a cold gearbox on a spring morning to a hot one after an afternoon of highway miles. That is the point of a high-index synthetic in a compartment that has to work the same cold or hot.

Setting the change interval and keeping the warranty intact

The fluid is recommended for up to 20,000 miles or one year, whichever comes first. That figure belongs to the product line rather than to any one motorcycle, so the maintenance schedule in the owner's manual is still the reference for a bike ridden in severe service.

Synthetic V-Twin Transmission Fluid is Warranty Secure and is backed by the AMSOIL Limited Warranty, so using it in place of the manufacturer-branded gearbox fluid does not put the factory warranty at risk. Riders servicing a V-twin gearbox and an ATV gear case on the same afternoon should note that the two take different products, and the machine side is covered by ATV/UTV Transmission and Differential Fluid.

Service life

V-Twin Transmission Fluid is recommended for up to 20,000 miles or one year, whichever comes first.

Typical technical properties

Typical properties published by AMSOIL, checked July 2026. These are representative values rather than a specification, and they change when AMSOIL updates a formula.

Package sizes and product codes

Select a product code to open that package size on the AMSOIL product page.

Product documents

AMSOIL publishes the full technical detail for this product in these documents.

• V-Twin Transmission Fluid product data bulletin (PDF)
• V-Twin Transmission Fluid safety data sheet (PDF)

Where to order

Confirm this formula is the match for the vehicle or equipment in the AMSOIL product guides, then order V-Twin Transmission Fluid online. Existing members can sign in to apply the discount automatically.

Details and questions