Some 2020-2024 Silverado 2500/3500 and Sierra 2500/3500 models equipped with the 10L1000 10-speed automatic transmission (RPO MGM, MGU) and four-wheel drive transfer case (RPO NQF, NQH) may have a fluid leak between the transmission and transfer case. If a fluid leak is found, it may be due to the transmission case extension seal or the transfer case input shaft seal.
The cavity between the transmission and transfer case is a wet cavity by design. The transfer case input shaft seal is a double seal to prevent transmission fluid and transfer case fluid from intermixing with each other. If either side of the seal leaks, fluid will leak from the weep holes between the transmission and transfer case. (Fig. 18)
Fig. 18
To help determine if the seal depth is incorrect, add dye to the transfer case or transmission. If the seal is installed too deep, the fluid leaking is transmission fluid. If the seal is not installed deep enough, the fluid leaking is transfer case fluid. Either condition will cause fluid to leak out of the weep holes between the transmission and transfer case.
If diagnosis indicates that the seal depth is incorrect, replace the transfer case input shaft seal (Fig. 19, A) and transmission case extension seal (Fig. 19, B).
Fig. 19
TIP: The transfer case input seal may be installed backwards, as a two-piece seal back to back, and the replacement seal may also come as two seals to be installed. Correct orientation if two seals are received is with the metal clad together, which may be rubber coated. The garner springs need to be facing opposite of each other with one spring facing the transfer case input gear and one spring facing towards the transmission output shaft. In addition, each seal may have three tabs — one seal with protruding tabs and the other seal with inverted tabs. The tabs are to be aligned for proper installation.
Review the latest version of #PIP5810 for proper transfer case input shaft seal installation. There are two design transfer case front case halves, and the seals install at different depths between design 1 and 2. Improper seal installation will result in repeat leaks.
In addition, be sure to follow the recommended transfer case alignment bolt torque and sequence pattern in the appropriate Service Information during the installation process.
Refer to #PIP5926A for additional information.
– Thanks to Thomas Ellison
Updated June 23, 2023
I don’t understand how the cavity is wet by design. If that were the case, then fluid would always drip out of the weep holes.