EF25520 | Genuine Eaton® Transmission Synchronizer Kit

1. Primary Transmission Families

The K-2446 synchronizer kit is engineered specifically for Eaton Fuller Heavy-Duty 9-Speed, 10-Speed, 13-Speed, and 18-Speed transmissions. It is commonly utilized in the auxiliary section of the transmission to sync the high and low range gearing. Common transmission series include:

• Eaton Fuller RT Series: (e.g., RT-14910, RTX-16710, RTLO-18918, RTLO-20918).

• Eaton UltraShift / AutoShift Platforms: Select generations of automated heavy-duty gearboxes.

2. Target Commercial Vehicle Fitment

Because Eaton Fuller transmissions are the industry standard for North American Class 8 heavy trucks, this kit fits a massive range of commercial vehicles equipped with these gearboxes, including:

• Freightliner: Cascadia, Century Class, Columbia, and Classic models.

• Kenworth: T660, T680, T800, W900, and C500.

• Peterbilt: 379, 389, 567, and 579.

• International (Navistar): ProStar, LoneStar, and 9900i series.

• Volvo & Mack: Older or custom-spec models built with Eaton powertrain options.

1. What is it?

Manufactured by Eaton®—the global benchmark in heavy truck drivetrains—the K-2446 kit contains all the precision-engineered components needed to replace a worn or damaged range synchronizer. It is located inside the auxiliary (rear) section of Eaton Fuller transmissions and is responsible for matching speeds when shifting between the low range (gears 1-4) and high range (gears 5-8/13/18).

2. Kit Components & Core Functions

• Synchronizer Assembly (Gold/Bronze & Steel Rings): Friction material matches the rotational speed of the main shaft to the output gear, eliminating grinding.

• Pins and Springs: Ensure the synchronizer sliding clutch engages accurately and snaps securely into position without slipping out.

• Smooth Range Transitions: It allows the driver to switch from low to high gear ranges smoothly under heavy loads, protecting the transmission gears from catastrophic teeth shearing.

1. Severe Gear Grinding During Range Shifts

The most common sign of a failing K-2446 kit is a loud metal-on-metal grinding noise when flipping the range selector switch on the shifter knob (transitioning from 4th to 5th gear, or dropping back down). This happens because the synchronizer’s friction material is worn flat, making it unable to match the speeds of the auxiliary gears.

2. Slow or Delayed Range Engagement

If you flip the range pre-selection lever and there is a noticeable multi-second delay before the transmission actually shifts into the next range—or if you have to let the engine RPM drop completely to complete the shift—the synchronizer rings are slipping and failing to grab efficiently.

3. Transmission Popping Out of Range (Slipping into Neutral)

If the internal springs, pins, or locking teeth included in the K-2446 kit are broken or stretched, the synchronizer cannot lock firmly into place. Under load or when coasting, the transmission may violently pop out of high or low range and drop into a "false neutral," leaving the truck without power.

4. Hard Shifting or Resistance at the Shift Lever

When the synchronizer assembly misaligns due to broken pins or warped rings, it creates physical resistance inside the shift tower mechanism. The driver will have to use excessive physical force on the gear shift lever to force the transmission into gear.

5. Bronze Shavings in the Transmission Oil

During a routine transmission fluid change, finding bright gold or bronze glitter-like shavings in the oil or stuck to the magnetic drain plug is a definitive warning sign. It proves that the bronze friction coating on the synchronizer rings is disintegrating and shredding away.