That clunking or whirring noise you hear probably means your four-wheel-drive, or 4WD transfer case is broken. The transfer case is a separate unit externally attached to the transmission. It transfers engine power to all four wheels when engaged. It can be expensive to repair or replace, depending on the issues, but first, you need to know what the issue or issues are. 

Is it or isn’t it the transfer case?

Certain issues generally relate to separate components inside of the transfer case going bad. But some can be more benign. For starters, make sure your fluid level is correct. Fluid that puddles under the transmission could be why transfer case fluid is low. 

Be vigilant about fluid changes every 30,000 miles, or whenever the manufacturer recommends. Also, refer to your owner’s manual when addressing a potential problem. It may be something as simple as not coming to a stop before shifting into 4WD mode. Now, let’s look at the main issues causing transfer cases to malfunction. 

Won’t stay in 4WD

If your 4×4 transfer case keeps popping out of 4WD, there might be a problem with the differential or driveshaft. But it could also mean a problem internally. The best recourse is to put it on a hoist and have a service tech look for the problem.

Shifting issues

If there is a problem shifting in or out of gears, it is usually an internal issue. But keep in mind that low fluid levels can also cause this to happen. And it could also be a damaged shift linkage, which behooves you to do an inspection of the linkages before taking it in for service. 

Hard to or doesn’t engage or disengage gears

There is a myriad of problems that could be causing this issue. A damaged shift linkage or electrical malfunction in the control system are just some issues possibly cursing the problem. Internal issues can also be a cause. 

Grinding, growling, or whirring noises

If you’re hearing noises, notice if they change as engine speeds change. This can indicate the issue is coming from the transfer case, according to S&G Gearbox. Among the numerous causes, the noises could be bad bearings, loose chains, or gears with damaged or missing teeth. But make sure your fluid level is where it should be. 

Some problems may be a result of something wrong with your transmission, or a damaged or unbalanced driveshaft. Unless you’re familiar with the gang of possible issues with or beyond the transfer case, it is best to have a service technician have a look. 

In some instances, it is better and cheaper to just replace the transfer case. But in most cases, it is far cheaper to have it repaired. Repair costs vary wildly, mostly based on the make of the vehicle. Try to get numerous quotes before stepping up to be assured of the least expensive best option. From what we have seen, the replacement costs can go from $2,500 to over $8,000.