Case Study: Chevrolet Tahoe Transfer-Case Leak


	Dave Riccio, Owner/Technician

By Dave Riccio, ASE Certified Technician, Owner of Tri-City Transmission & Auto Repair, Co-host of Bumper to Bumper Radio

CASE STUDY: Chevrolet Tahoe, Transfer-Case Leak

Tri-City Saves Another Chevrolet Transfer-Case

New Process, Model 246 - aka NP246

This customer owns a 1998 Chevrolet Tahoe, Four Wheel Drive. His regular mechanic spotted a transfer-case leak when he was in for service. They ended up replacing a front output seal thinking that was the source of the leak. While it may have been leaking, that's not the entire story when it came to the transfer-case leak.

This particular problem has been around for years, and is often mis-diagnosed by general repair shops as they don't see it as often as we do in an everyday transmission shop. Any transfer-case leak is a big leak when you consider the whole system only hold 2 quarts. As a rule of thumb, the modern transfer-case never fails with the exception of being run low on fluid or a tire mismatch problem. Other than that, they are pretty trouble free with good maintenance.

Let me explain what happens to this particular transfer-case along with a few others in the General Motors line up. The transfer-case housing is built of magnesium. At the back of the transfer-case is a fluid pump that disperses the specialty transfer case fluid throughout the transfer-case. That pump is made of an aluminum housing. There is spring steel (#7 Pictured) isolating the puzzle piece fit of the pump into the magnesium housing of the transfer case. It's a chintzy piece of spring steel that inevitable breaks or comes loose, creating slop between the aluminum transfer-case pump and the magnesium transfer-case housing. Each change in gear box direction bangs the pump up against the housing. This happens every time you are on and off the gas or go from park to reverse and reverse back to drive. You need to understand, this is what's happening on the inside of the transfer-case, so it is not seen by technicians until it is too late. The pump begins to break through the transfer- case housing and a pin hole is created. This hole is from the inside out and is big enough to slowly run the transfer-case dry on fluid. In most cases, it happens slowly that the vehicle owner never notices a leak in the driveway. This turns a minor problem into a major repair.

Case Study Chevrolet Tahoe Transfer-Case Leak | Chevrolet Tahoe Case Study Service Repair

If we have a customer who is open minded to preventative repairs, we will offer the installation of a case saver (#5). It is not a matter of if it will happen, but when it will happen. Open minded customers save themselves an expensive repair down the road if they heed our warning.

In this case, this gentleman's mechanic saved him from the major repair by spotting a leak that most overlook. After the front output seal did not cure the entire problem, he referred his customer here.

When we received the vehicle, we performed both a full diagnostic on the transmission and the transfer-case. It looked to be evident that the transfer-case did not have damage internally as of yet. In other words, it had been caught soon enough. When we disassembled the transfer-case, we found the broken spring steal (#7) and a hole worn in the case (#1 & #2). In years past we have weld repaired the hole in the case but welding magnesium is tricky and a bit on the dangerous side. With the invention of a quality case saver, we now repair the holes with a composite case repair kit overlaid with the case saver keeping the repair cost to a minimum (#5).

I have included pictures to better illustrate the issue at hand. This is not a repair most shops are providing. While we have the transfer-case apart, we fix other wear items like the common lever seal leak, fork pads and chain if needed all the while saving the customer from having to throw his transfer-case away.

We have repaired this particular transfer-case dozens of times with 100% success rate. It is a good repair that saves the customer a lot of money.

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Transfer-Case Background Information:

This design is in a myriad of general motors trucks. We have just highlighted one of the more recent ones where we performed the described repair. NP or New Process is the name of the transfer-case manufacturer. It is not made by General Motors, Chevrolet, or GMC. New Process's name has a few variations. It changed to New Venture and now has moved to Magnam International. There are three variations that we would point to that have this problem of the pump housing wearing through the magnesium case. NP246, listed here, NP261 and NP263. There are a few other variations but these stand out as the offenders.

We have included pictures of this repair as well as pictures of a failed transfer-case that was unrepairable that was at the GM dealership just months earlier where the fluids where supposedly checked. We do this everyday and believe me, an inexperienced or lazy lube tech like the one used at dealerships and independent auto shops alike is not checking your transfer-case fluid. It can be difficult on these models and the fill and drain plug are not always easily removed. Remember, most transfer-cases never go bad unless they are run low on fluid. Small leak, small capacity, big bill if not caught in time. Some lube technicians are known for pencil whipping inspection reports if its hard work. So, make sure your driveline fluids are checked by an experienced professional. That includes - Transmission, Transfer-Case, Front Differential, Rear differential.

Repair Order# 1032234, 02/05/19

Case Study Chevrolet Tahoe Transfer-Case Leak | Chevrolet Tahoe Case Study Service Repair