2015 GMC Acadia Transmission & Axle Gear Ratios

Transmission gear ratios

The 2015 GMC Acadia, like many of its GM crossover brethren, was equipped with a reliable 6-speed automatic transmission across all trims. This transmission, often referred to as the GM 6T75 or similar variants, was designed to provide a good balance of performance and fuel efficiency for the Acadia's target market. Below are the typical gear ratios you would find in this transmission.

Available axle ratios

The 2015 GMC Acadia offered a limited selection of axle ratios, primarily due to its unibody construction and focus on passenger comfort and fuel economy. The front and rear differentials (for AWD models) typically featured the same ratio to ensure proper operation. Axle ratios are crucial as they multiply the torque from the transmission, impacting both acceleration and fuel efficiency. Here are the common axle ratios available:

Note: While some vehicles offer a range of axle ratios, the Acadia largely standardized on the 3.16:1 ratio, which is well-suited for its primary role as a family hauler.

How to identify your axle ratio

Identifying the axle ratio on your 2015 GMC Acadia is relatively straightforward, primarily through the RPO (Regular Production Option) sticker. This sticker is typically found on the glove box door or sometimes on the driver's side door jamb.

1. RPO Sticker (Glove Box/Door Jamb): Look for a white sticker with numerous three-digit alphanumeric codes. These are your RPO codes. The code for your axle ratio will be "GH2" for the 3.16:1 ratio.

Unlike some heavy-duty trucks, the Acadia does not typically have an easily accessible metal tag on the axle housing itself that specifies the ratio.

Towing vs MPG impact

The axle ratio plays a significant role in balancing towing capability and fuel economy. Here's a breakdown of how the 3.16:1 ratio affects your 2015 GMC Acadia:

• Numerically Lower Ratio (e.g., 3.16:1): A numerically lower ratio means the engine spins fewer times for each rotation of the wheels. This generally results in:
  • Better Fuel Economy: At highway speeds, the engine operates at lower RPMs, consuming less fuel.
  • Reduced Towing Capacity/Performance: Less torque multiplication means the engine has to work harder to move heavy loads, potentially leading to slower acceleration and increased strain when towing at or near the vehicle's maximum capacity.

For the 2015 GMC Acadia, the 3.16:1 ratio is optimized for a balanced approach, favoring fuel efficiency and comfortable cruising, which aligns with its design as a family crossover. While it offers respectable towing for its class, it's not designed for heavy-duty hauling.

Common issues

While the 2015 GMC Acadia is generally a reliable vehicle, components within the drivetrain, including the differentials, can experience issues over time. Here are some common concerns to be aware of:

• Ring & Pinion Whine: A persistent howling or whining noise that changes with vehicle speed (and sometimes load) can indicate wear on the ring and pinion gears within the differential. This is often more noticeable at certain speeds.
• Carrier Bearing Wear: The carrier bearings support the differential carrier. If these bearings wear out, they can produce a rumbling or growling noise, especially when turning or accelerating.
• Limited-Slip Clutch Wear (if applicable): While not all Acadia models came equipped with a limited-slip differential in the traditional sense, the AWD system uses a power transfer unit (PTU) and rear differential. Wear in these components can manifest as clunking or binding during turns, particularly at low speeds.

It's important to address any unusual noises or vibrations from the drivetrain promptly to prevent more extensive and costly damage.

Find a driveline shop on Repairius.