Diagnosing Noises in Your Car
I’m going to group a few things together into this one: axles, transfer cases, and rear ends. Let’s start with transfer cases.
A transfer case is the mechanical component that connects the final drive output of the transmission to the front and rear wheels on a 4WD or AWD vehicle.
These can range from simple mechanical devices to highly sophisticated components that dial in a prescribed amount of power to the front and rear wheels. As a result of this, you don’t do too much servicing of a transfer case outside of fluid changes. So if you suspect a noise from the transfer case, replace the fluid with the correct fluid as dictated by the service manual and recheck for the noise. If the noise goes away, call it a win and move on. If not, you might have to replace or rebuild the transfer case. As I said, these run the gamut from simple mechanical devices to highly sophisticated, precision-engineered components. You really don’t want to get started here unless you know what you’re getting into.
The differential, or final drive, is one of the last links in the chain before power is delivered to the wheels. The differential serves a key function, which is to prevent wheel hop during tight turns while still delivering the engine’s power to the wheels. I’m not going to get into a long explanation of how differentials work, as we are mainly concerned with noises from the differential.
If your differential is making noise, it’s likely it needs service. Outside of changing the fluid, there is little you can do. Like transfer cases, differentials can range from simple mechanical components to sophisticated engineered parts; it just depends on the vehicle and application. Even simple differentials can be difficult to set up without the proper tools, so if you find that you have a noise coming from your differential, it’s best to leave it to a professional unless you have the tools and experience to tackle the job.
One thing to note on the fluid. You once again must use the correct fluid for best results. Some differentials are limited slip, meaning they deliver power to the wheels differently than a conventional differential. These differentials often require a special fluid or additive to be added to the oil for proper operation.
The funny thing is, these types of differentials are often the ones I find making noise. Much of that is due to improper service in the past. So heed the warning and use the correct fluid in your differential. It can save you a lot of money and headache later.
I’m singeing out Honda differentials here because I have a great deal of experience with them. The AWD (All Wheel Drive) model Hondas such as the CRV and Element often use a special fluid in their rear differentials. This fluid is called “double pump II”. Later, they switched to Honda ATF. On vehicles like the MDX, Ridgeline, and late model RL’s and TL’s, they use Honda VTM4 fluid. Be sure you know what fluid goes into your Honda differential and that you replace it with the correct fluid. The reason I bring this up is because I have seen Honda differentials cause noise from time to time. Often the first thing I do in this situation is change the differential fluid. The fluid should get changed about every 30,000 miles. If not, it tends to break down. When it does break down what is commonly heard is a nose on turns coming from the rear of the vehicle. This noise can often be cured with a fluid change. As stated you need to make sure you use the correct fluid. These fluids are specially designed to work with Honda differentials. Using the wrong fluid could result in damage to the differential. So if you have a noise coming from the rear of your AWD Honda, change the differential fluid with the correct Honda fluid and see if the noise goes away. In this video I show how to change the differential fluid in my 2004 Element.
There are two types of axles I’ll discuss here: rear wheel drive axles (RWD) and front wheel drive axles (FWD). We’ll start with RWD. I don’t often hear noises from the axles themselves, but I do hear noises from the U joints and center bearings if equipped. If you have a bad U joint, you’ll often hear a loud click or clunk when you engage drive or reverse. It might be worse in one direction than the other.
To confirm you have a bad U joint, simply grab the axle and twist it back and forth and move it up and down while you feel for looseness. Bad U joints are often obvious and will move around a bit if they’re bad. Sometimes they won’t be so obvious; in those cases, look for orange dust around the U joint caps. This indicates a lack of lubrication and often a loose part.
If you find a loose U joint, replace it. You really can’t make them better any other way. I recommend you install U joints with serviceable fittings so that you can lubricate them in the future. This will ensure that the U joints last a good long time. It’s usually a lack of lubrication that kills them in the first place. One last tip: Install the grease fitting toward the axle; this will make it easier to service later.
As for center bearings, this can be tricky to track down. These are bearings that are used with particularly long drive shafts where they’re split into two pieces. They use a center bearing to support the drive shaft over this long distance.
I’ll admit it’s difficult to diagnose a noise from this area, mostly because they often make noise under load, which means you can jack the vehicle up and run it and never hear the noise. Drive down the road, however, and the noise is there.
The best advice I can give you here is to try to get your hands on a chassis ear. This is a tool that uses tiny microphones that you place on different parts of the vehicle to help you find noises.
These tools aren’t cheap, and I don’t believe you would be able to rent one from your local auto parts store. They’re mostly found in repair shops and are used to track down difficult noises. That said, if you have or suspect a bad center bearing, replace it. Once again, these parts aren’t serviceable, so you’ll need to replace them if you find a bad one. You may find that you need to replace the entire axle assembly. If this is the case you might consider finding a salvage unit. If you do it may save you quite a bit of money.