2015 Ram 1500 Transmission & Axle Gear Ratios

Transmission gear ratios

The 2015 Ram 1500 offered a few transmission options, depending on the engine and trim level. The primary transmissions were the TorqueFlite 8 (8HP70 and 8HP75) eight-speed automatics and, for some configurations, a 65RFE six-speed automatic.

ZF 8HP70 Eight-Speed Automatic (5.7L HEMI V8, 3.0L EcoDiesel V6)

ZF 8HP75 Eight-Speed Automatic (3.6L Pentastar V6)

65RFE Six-Speed Automatic (Earlier 5.7L HEMI V8 models, lower trims)

Available axle ratios

The 2015 Ram 1500 offered a range of axle ratios to suit various needs, from fuel economy to heavy-duty towing. Most trucks came with an open differential as standard, with an anti-spin (limited-slip) differential often available as an option.

How to identify your axle ratio

Identifying your Ram 1500's axle ratio is crucial for proper maintenance, modifications, or simply understanding your truck's capabilities. Unlike some manufacturers, Ram (and previously Dodge) trucks typically don't have a simple RPO code sticker on the door jamb for axle ratios directly. Instead, you'll usually find the axle code on a sticker inside the glove box or, more reliably, on a metal tag attached to the differential cover or one of the differential cover bolts.

1. Glove Box Sticker: Check the sticker in your glove box for a three-digit code that might correspond to your axle ratio. This is not always present or clear, however.

2. Axle Tag: The most definitive way is to look for a metal tag on the rear axle housing. This tag will typically show the gear ratio stamped on it (e.g., "3.92"). If the tag is missing or illegible due to rust or damage, you might have to resort to counting gear teeth or using a VIN decoder.

3. VIN Decoder: Many online VIN decoders can provide your vehicle's original build sheet, which will list the factory-installed axle ratio. This is often the easiest and most accurate method if physical tags are obscured.

4. Visual Inspection/Tire Spin Method: With the vehicle safely supported on jack stands and the transmission in neutral, mark a tire and the driveshaft. Rotate the tire exactly two full revolutions and count how many times the driveshaft rotates. If it rotates approximately 3.92 times, you have a 3.92:1 ratio. If it's closer to 3.55, then it's a 3.55:1, and so on.

Towing vs MPG impact

Your truck's axle ratio has a significant impact on both its towing capabilities and fuel economy. It's a trade-off: what's good for towing is generally not ideal for fuel efficiency, and vice-versa.

• Numerically Lower Ratios (e.g., 3.21:1): These ratios mean the engine has to turn fewer times for each revolution of the wheels. This results in lower engine RPMs at highway speeds, which generally translates to better fuel economy. However, with less mechanical advantage, the engine has to work harder to get a heavy load moving or to pull it up an incline, reducing towing capacity and increasing strain.

• Numerically Higher Ratios (e.g., 3.92:1): With these ratios, the engine turns more times for each wheel revolution. This provides greater mechanical advantage, allowing the truck to tow heavier loads more easily and accelerate quicker, especially from a stop. The trade-off is higher engine RPMs at cruising speeds, leading to decreased fuel economy.

For the 2015 Ram 1500, a 3.21:1 axle is best for drivers who do a lot of highway driving and rarely tow heavy loads. The 3.55:1 ratio offers a good balance for general use, handling moderate towing while still providing reasonable fuel economy. The 3.92:1 ratio is the clear choice for those who frequently tow heavy trailers or operate in hilly terrain, prioritizing towing performance over fuel efficiency.

Common issues

While the 2015 Ram 1500 drivetrains are generally robust, like any mechanical components, differential and axle assemblies can experience wear and tear. Some common issues include:

• Ring and Pinion Whine: A persistent howling or whining noise that changes with vehicle speed and often with acceleration/deceleration can indicate worn or improperly set up ring and pinion gears. This is more common after improper gear changes or if lubrication has been compromised.
• Carrier Bearing Wear: The bearings that support the differential carrier can wear out, leading to a rumble or growl that typically becomes louder with speed. If left ignored, this can lead to more significant damage.
• Limited-Slip Clutch Pack Wear: For vehicles equipped with an anti-spin (limited-slip) differential, the clutch packs can wear out over time. Symptoms include a chattering or grinding noise (especially during slow turns), or a noticeable decrease in traction when one wheel loses grip. Regular fluid changes with the correct friction modifier are essential to prolong the life of these components.

Regular differential fluid changes using the manufacturer-specified fluid and friction modifiers (if applicable) are critical for preventing premature wear and extending the life of your axle components.

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