Reader Question I have a 1999 Jeep Cherokee 4X4. It has 107K in it. Ever since it passed the 80K mark, it has developed a hum in the front end that has gotten worse and worse over time. I recently had 4 new tires put on and I had the u-joints replaced in the front end when they put the tires on. It improved the noise slightly but obviously that wasn’t the problem…. Any suggestions on what I should try next?? thanks
Does this hum noise get louder the faster you drive? My first suggestion is ALWAYS check the tires, especially in 4X4 vehicles with more aggressive tire patterns. If you have a non smooth, non highway tread on your tires….it WILL make noise. Since the noise did change some with the new tires, it leads me to believe the problem is in the type of tread on the tires….probably more of an off road tread than a highway type tread you would find on a normal 2WD Jeep with standard radial tires….right??
The only other thing that might cause your noise would be the front….or rear differential. Noises can be tricky to determine where they come from…front or rear. You might want to take a test drive on an large open vacant parking lot and try this – get the vehicle up to the speed where you hear the noise, turn off the engine (don’t turn the key all the way back or it will lock the steering wheel) and let the vehicle come to a coasting stop by itself without the use of the brake.
This will help eliminate other noises like engine and transmission and will let you hear the noise better. See if you can tell if it really is coming from the front of the vehicle…I usually hang my head out the window so I can hear outside the vehicle.
I would do this on concrete and then on asphalt to compare the noise on different surfaces…if the noise is different…its gotta be a tire noise, since that is the only thing touching the surface. If the noise is the same, It could be from a noise differential gear or bearing, you should have both differentials checked and make sure they are full of fluid.
The BEST way to check the differential for noise is to run the vehicle in gear in 4X4 mode while it is on a lift in the air. You can then take a stethoscope and listen to the differential covers.
I wrote this awhile back – it might also help you determine if you do have a noisy differential
Austin C. Davis
Reader Follow up
Im almost positive its not the tires, and it does get louder as you pick up speed…it gets pretty bad at 65 or 70..my tires are not overly aggressive treadwise and I know it’s the front end not the rear…so it must be that front differintial.
If you can get the vehicle up in the air, and engage the front tires at 65 mph while on a lift…you can listen to the differential. Don’t try this at home with jack stands!!! Overhauling a differential can be expensive, and I have heard some loud noises coming from them…that have been that way a long time. So, you might not have to run right out and repair it.
Lastly, drive 65 in 4×4 mode…give it gas then let off the gas pedal…if it is the differential you should hear a change in the pitch of the noise…since you are applying pressure to the gears then letting off.
I have used an over the counter differential additive to help quiet some noisy gears…it helped some, but hopefully protected the gears and bearings from future wear.
Keep me posted as to what you find.
Austin C. Davis