In 1999, General Motors introduced the GMT800 full sized truck platform. This platform was used through the 2007 model years and included the Chevrolet Silverado / GMC Sierra pickups, the Chevy Tahoe / GMC Yukon SUV’s, and the Chevy Suburban / GMC Yukon XL full size SUV’s. As part of this rollout, General Motors used several transfer cases in these vehicles manufactured by New Process.
One of the most common lines of transfer cases from the 2000s had an embedded weak point that is costing many customers thousands to repair if not proactively addressed before a failure becomes present. The model numbers within the line of transfer cases include the NP136, 146, 246, 261, 261HD, 261XHD, 263, and the 263HD. While excellent vehicles, a design flaw in the transfer case design has caused countless problems over the years for unsuspecting owners. Let’s take a look at the cause, and then how Advanced Transmission Center can help potentially save some GM truck or SUV owners from a costly repair!
What is a Transfer Case?
A transfer case is used on 4-wheel drive vehicles. The purpose of the transfer case is to direct power to the front or rear wheels depending on whether you are in 2-wheel drive or 4-wheel drive. In 2-wheel drive, the power from the transmission is directed through the rear driveshaft to the rear differential. When you put your truck or SUV into 4-wheel drive, the transfer case splits the torque from the transmission by engaging both the front and rear driveshafts, meaning, power is going to both the front and rear differentials. Where older transfer cases were gear driven and had only a single gear ratio, modern transfer cases usually use a chain drive and have 2 gear ratios to provide more power options depending on driving conditions.
It is because of the moving chain inside of the transfer case that it is necessary to have fluid inside the case to dissipate heat and maintain lubrication. This requires a pump inside of the case to circulate fluid while operating. These units either carry Auto-Trak II fluid or automatic transmission fluid. Both of these fluid types will degrade over time and should be serviced on a regular basis. Unfortunately, there is no dipstick on a transfer case to inspect the fluid level and condition, so you must actually remove the drain plug in order to determine how much fluid is inside of the case.
The problem with many of these transfer cases is the pump design in relation to the case. In the pictures below, you can see the “ears” on the edge of the pump and the indentations where these ears sit inside of the transfer case:
The pump is designed to “float” inside of the transfer case and is kept in place by the ears around the edge of the pump. However, over time these ears wear down (and even break off) which allows the pump to begin rubbing against the inside of the case. In order to save weight, GM made the case out of magnesium. Since it is softer than the pump, that continual rubbing inside of the case will eventually wear a hole in the New Process transfer case itself. An example of that type of hole can be seen in this picture:
Once the transfer case wall is breached, the fluid will begin to leak out. The hole in the image may seem inconsequential, but the reality is grave. The problem is that the design is such that the hole is sitting above the level of the drain plug, so it doesn’t leak while the vehicle is stopped. As a result, you won’t see any leaks on your driveway or garage floor to let you know you have a problem. However, when the vehicle is running and the pump is pressurizing the fluid, it will begin to escape through the hole in the case. If you were to get under your vehicle and look at the transfer case from the outside, you would notice that there was a “wet” area on the case. You might also notice that the fluid has splashed back on the underside of the vehicle and maybe on anything you might be towing. Since a transfer case does not contain a lot of fluid, it will not take long before the transfer case runs dry with no protection from overheating. When it does, a LOT of noise and a catastrophic failure are not far behind!
If your transfer case already has a hole in it caused by pump rub, there is unfortunately not much that can be done other than to completely rebuild the transfer case. This will include replacing the case half that has the hole in it and is not an inexpensive repair. Like a transmission, a certified drivetrain specialist should complete this rebuild procedure. Having the transfer case rebuilt in a situation like this will cost you several thousand dollars.
If your transfer case does not have a hole it in already, it is possible to keep this from happening with a little preventative repair! The technicians at Advanced Transmission Center can install a “case saver” that will prevent the pump from moving around and rubbing against the inside of the case. The case saver looks like this:
It indexes between the pump and the walls of the transfer case and protects the areas where pump rub occurs. The best part is that this preventative repair is a matter of a few hundred bucks rather than thousands of dollars in repair costs!
Transfer Case Rebuild & Repair Experts
If you drive a GM / Chevrolet truck or SUV built between the years of 1999 and 2007, this is an issue that you want to address before it becomes a truly expensive repair. The Advanced Transmission Center team consists of technicians who have decades of experience diagnosing, rebuilding and repairing transfer cases in domestic and import vehicles. We have the ability to test and diagnose problems with pump rub inside of your transfer case and use only quality parts in our repairs.
If you are having problems with your transfer case or any other driveline related issue, contact Advanced Transmission Center at either of our locations and we’d be happy to help! Unlike dealerships or many independent repair shops, we are transmission specialists trained to fix issues related to a vehicle drive-train. You can reach out to either location that is most convenient for you.
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Please give us a call or send us a message ASAP. We look forward to serving your vehicle drivetrain and transmission needs. Over 35 years, our goal remains to be “Geared for Customer Satisfaction!