blazer 2008

Trying to diagnose front end hum no vibration . Even at low speed at 30 mph. Replaced fr. tie rods etc.but not fr. hub or fr. u joints .I read removing fr. driveshaft to see if stopped noise ,does this apple to a 89 jeep cherokee 4.0 auto basic pull lever to engage 4 wheel. Never in 4 wheel drive. Is my first 4x4 but I do know how to fix stuff but not much knowledge on jeeps

Garrett S.

Removing the driveshaft can help. You also might try rotating your tires to see if the sound follows a tire.

blazer 2008

Thanks , I did the tire shake to check hubs no play, don,t know how to check fr. u joints but see what I can find on the interweb

PatHenry

Removing the driveshaft will tell you if the hum is related to the driveshaft - So this could be Transfer case yoke, driveshaft itself or front pinion. The typical failure is in the driveshaft u-joints, but it is possible it is in either the axle yoke or TC yoke bearings - the removal of the "load" (aka extra force required to move the driveshaft) can reduce bearing noise.

Once you remove the front driveshaft, move the u-joints with your hands (being careful not to pinch your fingers in the double cardan cv joint) and see if you can feel any roughness. An obvious sign of u-joint failure is if you twist on the driveshaft and there is ANY play in the u-joint at all.

Checking the hubs can be done by pushing on the tires, but it's not definitive. You can also spin the tire with it jacked up and see if you hear anything or feel any roughness. Hub bearings are also a common failure (and even more common if they are replaced and the axle nut is not torqued to the proper 180 ft/lbs).

You can also have a bad AXLE u-joint - these are the u-joints in the axle shafts that sit inside your front axle tube.

All of these things can fail even if you never use 4wd. The front driveshaft and axle shafts still spin when the vehicle is moving regardless of whether 4wd is engaged or not.

My suggestion -
1) Remove the front driveshaft and drive around and see if the hum is gone. If so, closely inspect the driveshaft and yokes. ANY play in the yokes (up-down, side to side, forward/backward) is bad news.
2) If the hum remains and is unchanged, I would suspect the wheel hub bearing.

Interestingly enough, I just pulled my front driveshaft last night to diagnose a drive-line noise and slight vibe. I knew the axle side u-joint was bad but when I started manipulating the double-cardan joint I could feel a bit of roughness in there as well - so a full front driveshaft rebuild is in my near future.

blazer 2008

Thanks, I,ve been chasing fr. end noise for awhile , old fr. tie rods were starting to go and swinging up and down so replace which helped , then new sway bar bushing but had to cut some material out so it would tighten snug . The noise isn,t bad but just annoying .I don,t drive on the hi-way just in town so I,m not going 70 mph..It always happens just before winter when things go bad . I,ll see what I can do if not I,ll wait till spring , only 3 months of snow here so I can drive my old single wheel drive truck till the snow comes. A hub looks pretty easy to do at home. Thanks for the help ,there isn,t much of a Jeep community here except the new ones

cruiser54

Pull that front shaft. and while you've got it out carefully inspect the deal between the double u joints at the transfer case end. They're rarely ever lubed because it's darn near impossible to do with the shaft in the Jeep.

PatHenry

The hubs are pretty easy. You need the 36mm socket for the axle nut and a 13mm 12-point socket for the hub bolts. The biggest hurdle that people have is getting the hub out of the knuckle. Look up the trick for sticking a deep socket or bolt against the axle shaft ear and axle body and popping it out using the steering. That works great.
I just did a hub in my dirt driveway, at night, with limited light and it took roughly an hour and a half from start to finish without rushing. Since I was replacing the hub I used a MAP torch on the axle nut and it came off pretty easily with a breaker bar. If I was JUST replacing the axle shaft u-joint I wouldn't use heat on the axle nut since I wouldn't want to damage the hub.

When putting it back together, you MUST torque the axle nut to 180 ft/lbs - if you don't torque it enough then the hub bearing will fail prematurely.

blazer 2008

New clue .Thanks ,I changed fr. tires to my summers which are a little wider [225/75/15] and noise was still there but with the wider tire I could feel more and was really noticeable turning at low speed.Most of the noise is at low speed,I guess at a faster speed most things seem to float and not cause so much noise.