99 Jeep Grand Cherokee Laredo
4.0 6 Cyl, Auto Trans, Selec-Trac
63,000 miles

Excessive noise developed from what I think is the front differential while traveling above 30 mph. Transmission shifts fine, and the transfer case seems fine in all ranges, too. Fuel economy is actually better than ususal, and noise is not from the tires. The noise is kind of like a constant hum/grind and grows louder as speed increases. I can feel the noise through the brake (all are ok) pedal and steering wheel, but it is smooth on the gas pedal. Oil levels are all ok in all diffs and xfer case.

It just feels like it is coming from the front, but I also noticed an oil leak on the right rear wheel and brake shield -- could this mean that that bearing could go next if the oil level in the diff got low? Or would one seriously suspect this to be the culprit? At any rate a new seal is in order. Difficult to change?

If this is a wheel bearing, should they be replaced in pairs?

Thx in advance

I have heard that it is a very common problem to have the bearings in the differentials to go bad, I am replacing my now. It started off as a sound that sounded like you had off road tires on, then it got a little louder and had to turn the radio up a little louder. My seal went out on my rear end and started leaking fluid and when i moved the driveline, i could feel a lot of play in the yolk going into the diff.. The dealer stocked tons of these bearings and seals, saying they have people coming in every day to change these out.. I am changing both the pinion bearings and axel bearings and the seal.. my price was 210 bucks.

Just some ideas for you to think about and check out.. Good Luck finding your problem

Sounds like its time for a wheel off inspection to look at the brakes, wheel bearings (front and rear) and maybe a diff service to look at the oils.

You'll have to pull the rear diff cover to get at the rear axle seals.

a grind noise and a hum noise are not that close so it could be two different problems too. when you drain the diff oil, catch it in a clean container so you can see any metal that is floating around and check the bottom of the housing for anything that might have settled there.

If it is a wheel bearing, the other side should be inspected and replaced if necessary or you can replace it just to be sure. The bearing and seal are not that expensive - just a little more labor is necessary.

Are you intending to do the work yourself??


JD

Yes, I plan to do the work myself.

If the pinion and ring gear are worn, is there some type of lubricant to lessen the noise and allow continued use before replacement?

It is unlikely that the ring and pinion gear are causing the problem. more likely the bearings if the noise is in the differential.

When it is the ring and pinion making the noise we used to use saw dust to quieten things down for a while but thats not recommended - especially if you are going to keep the car.

If you are planning on doing any work yourself- diff or what ever - you NEED a manual. some times you can improvise on some of the special tools but you need a manual.

JD

Had the same noise on my 97. Front differential carrier bearings were bad. Checked the magnetic drain/fill plug - never could find much metal, but took it to a shop that specializes in differentials. $520 and one day to have them do the job. No more noise.

JD and all Thanks for your input...

I do have a Haynes manual; it is not so great as most of the focus are pre-99 GJCs. I have had both wheels off and am going to attempt the front wheel bearings/hubs first.

For some reason the rear disc rotors are stubborn to come off prior to accessing the bearing seal/housing -- any ideas?

Make sure that the parking brake is off and the parking cable is backed off. Most rear disk brakes use the center of the hub for parking brakes.
Ed
web/gadget guru

JD and all Thanks for your input...

I do have a Haynes manual; it is not so great as most of the focus are pre-99 GJCs. I have had both wheels off and am going to attempt the front wheel bearings/hubs first.

For some reason the rear disc rotors are stubborn to come off prior to accessing the bearing seal/housing -- any ideas?

For some reason the rear disc rotors are stubborn to come off prior to accessing the bearing seal/housing -- any ideas?

Is the rotor tight to the axle end or loose a little.

If tight, use some penetrating oil and a couple of sharp hits between:grinyes:the studs with the ball end of a ball peen hammer. Some vehicles use two retaining screws to hold the rotor to the axle end but I've not seen that use on a Jeep yet.

If slightly loose, then like Tech Ed says, Make sure that the park brake is fully released. There may be a rubber plug on the bottom half of the backing plate. Remove it and shine a light in the hole to have a look for the adjuster. Us a small screw driver to turn it to back the shoes off a bit.

They should come off easily after that.

Not sure if the 99 is the same park brake arrangement as my 96, but mine has a pivot in the in the apply lever at the top of the shoe that siezed up and kept one side partly applied and ruined the lining so you might want to look into that while you have the rotors off.

One other thing - if you have a digital camera you might find it handy to take a quick picture before you disassemble things so you can refer to it and help get things back together the same way again.

JD

Whew! That hub was a bear.

I started with the front left side first as this was where it was thought to be the loudest.

After about 30 minutes of pounding (eventually a slide hammer) and liberal shots of penetrant, the hub came off -- it split in two with the casting being left on the spindle casting. I was able to pound a little more and rotated the casting. Then I threaded some bolts from the front side of the hub as jack screws -- off it came.

Now that it is replaced, the sound is still evident -- the problem must be the ring/pinion and/or carrier bearings. Anyway, the bearing needed replacing.

Thx, for the continued advice.