ATF LEAK
I own a '05 GMC with the Duramax/allison. I love this truck. I bought it new and only use it to tow our travel trailer between our summer home in New York and Tampa, Florida. I've been seeing a spot or two of ATF on my garage floor the past couple of weeks. It's not dropping from the transmission but behind it some distance. I suspect it may be coming from the transfer case but not from the rear seal.
The local dealer tech suspects the gasket that fits between the two halves of the transfer case is leaking. How can that be? After doing a little online research about this problem, I found a tiny pin hole on the rear case half. My question is: do I need to remove the whole transfer case or can this problem be resolved from under the truck?
I'm a retired automotive systems design engineer and can still do most basic repairs. I just need the best advice so I don’t have to reinvent the wheel.
Thank you, Kaleb Woolsey Mayville, NY
Hi Kaleb,
Some New Venture Gear 261 (manual shift) and the NVG-263 (electric servo shift) transfer cases have developed an ATF leak due to the flange on the internal fluid pump wearing a hole through the rear case half. If not caught soon enough, the transfer case could suffer complete failure because of a lack of lubrication. GM'S original fix was to apply a JB Weld epoxy patch over the hole, and that is what I’d recommend for a temporary on-the-road fix. The most reliable long-term solution is to either buy a new rear case half or weld the hole(s) closed (hard to do on a magnesium case). Then you should install an aftermarket pump wear plate that permanently solves the problem. You really need to remove the transfer case to do a good job. Gravity will work against you if you attempt to repair the case half from beneath the truck. It may be possible to split the case halves and complete the repair without removing the transfer case, but it'll be a lot harder. There is no gasket used between the two case halves— just silicone sealant. Before re-assembling, clean the case mating surfaces using brake cleaner, then apply a 5-mm bead of RTV gasket compound to the flange on the inboard side of the bolt holes. Having the forward half of the transfer case mounted vertically on the bench helps the rear half slide over the various shafts and fittings during reassembly. This allows gravity to work for you instead of against you. Unbolting and removing the transfer case from the truck’s Allison usually ruins the gasket that seals the transfer case to the transmission adapter. You’ll need a new gasket. BOLT TORQUE SPECS: Crossmember to Frame Bolts: 51 lb-ft
Transfer Case Drain Plug: 15 lb-ft
Transfer Case Fill Plug: 15 lb-ft
Transfer Case Shield Bolts: 15 lb-ft
Transfer Case Speed Sensor: 11 lb-ft
Transfer Case to Transfer Case Adapter Nuts/studs: 36 lb-ft
Transfer Case Adapter to Transmission Bolts: 36 lb-ft Transmission Mount to Crossmember Nuts: 29 lb-ft Transmission Mount to Transfer Case Adapter Bolts: 34 lb-ft The GM transfer case requires 1.9 quarts of Dextron ATF. I recommend using a quality synthetic because of the somewhat limited amount and because the transfer case can run warmer than the transmission. For a wear plate that will prevent a future problem, visit Pacific Performance Engineering’s website (www.ppediesel.com) for the inexpensive “Adapt-a-case” wear plate or any related parts. Let me know if you need any other help.