2018 Jeep Grand Cherokee: Transmission & Axle Gear Ratios

Transmission Gear Ratios

The 2018 Jeep Grand Cherokee was offered with three different automatic transmissions. The primary transmission across the lineup was the ZF 8-speed automatic, which had different variants depending on the engine it was paired with.

850RE 8-Speed Automatic (3.6L V6)

8HP70 8-Speed Automatic (5.7L V8, 6.4L V8)

8HP95 8-Speed Automatic (6.2L Supercharged V8 - Trackhawk)

Available Axle Ratios

How to Identify Your Axle Ratio

Unlike GM vehicles with a door-jamb RPO sticker, or Ford/Ram trucks with an axle tag, Jeeps make it a bit more challenging to identify your axle ratio. The most reliable methods are:

• Original Window Sticker: If you have the original Monroney window sticker for your vehicle, it will list the "Final Drive Ratio" under the standard or optional equipment section.
• VIN Decoder: Many online VIN decoders can pull up the build sheet for your specific Grand Cherokee, which will detail the axle ratio it was equipped with from the factory.
• Jeep Customer Service: You can contact Jeep customer service with your VIN, and they can provide you with a build sheet that lists all the original components of your vehicle.
• Axle Tag (if present): While less common, some axles may have a metal tag bolted to the differential cover. This tag will have codes stamped on it, which can be deciphered to determine the ratio. It might directly state the ratio (e.g., 3 45) or have a code that corresponds to it.

Towing vs MPG Impact

Axle ratios have a direct and significant impact on both a vehicle's towing performance and its fuel economy. The relationship is a trade-off: what's good for one is generally detrimental to the other.

• Numerically Higher Ratios (e.g., 3.70): These ratios are often referred to as "shorter" gears. They multiply the engine's torque more effectively, allowing the vehicle to pull heavy loads with less strain. This makes them ideal for towing. The downside is that the engine must run at higher RPMs at any given speed, which increases fuel consumption.

• Numerically Lower Ratios (e.g., 3.27): These are known as "taller" gears. They require the engine to turn at lower RPMs to maintain a certain speed. This is great for highway cruising and maximizing fuel economy. However, because they don't multiply torque as much, they can make the vehicle feel less responsive and reduce its maximum towing capacity.

For the 2018 Grand Cherokee, a 3.45 ratio provides an excellent balance for daily driving and occasional light towing. For those who prioritize fuel economy on long commutes, the 3.27 is preferable. If you plan on frequently towing a boat or trailer near the vehicle's maximum capacity, the 3.70 ratio is the best choice.

Common Issues

While the ZF-sourced 8-speed automatic transmissions are generally considered robust, and the axles are well-built, some issues have been noted by owners, particularly as the vehicles age.

• Ring & Pinion Whine: A whining noise from the rear differential, which changes pitch with vehicle speed, can indicate a problem with the ring and pinion gear set. This could be due to improper backlash or wear.
• Carrier Bearing Failure: The bearings that support the differential carrier can fail, leading to a rumbling or grinding noise from the axle. This is more common on vehicles that are used for frequent heavy towing.
• Limited-Slip Clutch Wear: On models equipped with a limited-slip differential (LSD), the internal clutch packs can wear out over time. This can result in a chattering or groaning sound when turning, and reduced traction in low-grip situations.

Regularly changing the differential fluid with the manufacturer-specified type is crucial for maximizing the life of these components.

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