89 Limited: Drivetrain Noise: Loud hum and issues with 4wd

89 Limited, auto AW4.

I noticed while driving the jeep a loud hum coming from the front area of the jeep. I already know I have a toasted passenger side U joint and am going to replace that asap. However, this hum is loud and consistent. It happens any time the vehicle gets past about 15 mph.

Today I also tested the 4wd by putting it in 4wd hi and I could hear the bad joint. When shifting the vehicle back into 2wd there was a loud clunk and then binding followed by two or three more loud clunks. The vehicle then went back to just the hum I explained earlier.

What should I look for in the front diff? What else should I be inspecting and preparing to replace/swap out?

What transfer case? NP231--2wd/4hi/N/4lo? If so, you probably have a D30 CAD--vacuum disconnect--axle in the front. Poor vacuum level or a failing vacuum motor on the axle would be suspect.

Mine has Part time, 4 hi and 4lo. If this is a D30 CAV would this issue explain the hum as well.

The way the steering was previously binding while turning sharp left led me to believe that the 4wd was at least partially engaged still.

stockli said:

Mine has Part time, 4 hi and 4lo. If this is a D30 CAV would this issue explain the hum as well.

The way the steering was previously binding while turning sharp left led me to believe that the 4wd was at least partially engaged still.

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If the locking collar is failing to fully disengage that would make the front noisier.

Testing--see my post here: http://naxja.org/forum/showthread.php?t=980642

I just looked under my jeep, just got back from out of town and there is no vacuum system on this axle. I looked on the passenger side and saw nothing there just a solid axle. I looked everywhere and found nothing that looks like the part in question (i googled it to see what it looks like)

What else could it be? Amongst a million things lol

stockli said:

I just looked under my jeep, just got back from out of town and there is no vacuum system on this axle. I looked on the passenger side and saw nothing there just a solid axle. I looked everywhere and found nothing that looks like the part in question (i googled it to see what it looks like)

What else could it be? Amongst a million things lol

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Somebody has switched out your front axle--a popular mod.

Axel u-joints, unit bearings should be checked.

Also, the only 4wd you can use on hard pavement without binding things up is the FULL-TIME option of the NP242.

The shift pattern matches the one for the np242.

I know this will make a huge difference, sorry about not specifying the proper tc in the beginning.

No problema!

Reserve the 4hi/4lo for surfaces that allow differentiation of the axles--sand, dirt, mud, rocks, ice--hard dry cement or asphalt is a no-no.

Definitely look at the axle u-joints and unit bearings, post up what you find.

Good luck.

Will do, thank you!