Yea it does, I've noticed I see it more with the rpms, the higher the rpms (2000 and above) the worse it gets, however if I'm coasting at speeds there is nothing and if I'm at 40 and above and let off the gas entirely there is another sound, not the roaring but a kind of whirring.

And by safely I'm assuming you mean jack it up on both ends and take off the wheels and throw them under or something?

Regardless its been about a week now of me nagging them to give me the exact list of whats wrong and with little to no communication on their end, when I was leaving they didn't have the list ready because they had to look up the part cost of the rediff, but that shouldn't stop them from giving me the actual list of issues. Which is part of my reason I want a second opinion. I also brought it to a pep boys so I might do as PatHenry mentioned and take it to a real Jeep specialist. I do feel that they were probably right about a good deal, but at the least I want a write up from a professional.

Anyhow thanks for the advice guys, have an idea of where to go from here.

 

I might do as PatHenry mentioned and take it to a real Jeep specialist.

My brother does this all the time when he can't figure out his ride. Takes it to Monroe or somewhere, gets the diagnosis and quote, then says Thank You and leaves. Hey, they're in that business, and they charge a plenty for what they do, so why not.

 

I have a 98 XJ 2wd and just put it on the road after a 2-year lay up. I have a low rumble sound that I can't isolate. The brake rotors are not true and shudder when braking. That's an easy fix but doesn't explain the rumble noise/vibration that occurs at 30 mph and gets louder as speed increases. I have a 96 and the only sound I have is tire noise in the cabin. I put the same tires on the 98 to keep things standardized between them.

Another mechanic friend went on a drive with me today and said with certainty that the right front hub was the cause and he could feel it transmitting through the passenger floor board. I checked that hub and it's in good shape, no play and rotating silently.

I'm going to move back to the differential this weekend, drain it and remove the cover to give it an inspection. The truck was given to me by a friend so I have some flexibility. If it means rebuilding the differential I can budget it.

 

If you have another XJ with compatible tires, you can swap tires between the Jeep's and make sure it's not just bad tires. If it sat for 2 years and didn't move you could get bad vibes from the tires. I chased a vibe for a month once, certain it was a part and it couldn't be the tire since it looked awesome and had no miles on it.. Nope - bad tire. I learned then that a 13 year old tire that has been exposed to the elements is NOT the same as a new tire - even if they both have the little hairs on the tread.

 

I have no shame taking my Jeep to have just an inspection/diagnosis. I pay for their time and it's understood that I do everything I can myself but if I need work then I have no shame in having it done.

 

My 2000 XJ already has an 8.25 in it and it's a baseline Sport 4dr 4x4. He should check with his mechanic who should know because he worked on it. He could also run his VIN for the build sheet. Trying to explain about the shape of the cover could get confusing to someone who is unfamiliar with what to look for. If you're going for a rebuild and don't have a professional driveline shop nearby, check with any heavy truck repair shops. I'll bet they would love to fix a little one!

As far as the brakes are concerned, it's probably caliper pins that need to be lubricated.

 

Has anyone used an axle swap kit for the 8.25? Just curious, obviously the junk yard swap is cheaper but I'm thinking there is an element of certainty that comes with have kit (new parts, the correct parts, etc.).
Thanks!

 

What kind of kit - like a whole axle assembly or just some subset of parts?

I haven't seen anyone selling a "new" C8.25 axle and most of the kits seem to be for non-plug and play swaps (like using a Ford 8.8 or other "mod-required" unit).

 

For just under 4 grand, Quadratec will sell you a fancy D44 based axle that they list as being compatible with all XJ years. They also specify it as a "welding required" level of difficulty - so that IS an option if you want a super high end "new" axle.

As far as axle rebuild kits that contain all the bearings, seals, maybe even ring and pinion - absolutely these are a good choice just for the fact that they include all the little bits and bobs - it still requires a good deal of know-how from the installer to get it put in and working correctly of course.

 

All of the above is good advice I'll just add that a whining diff isn't necessarily a sign of failure. My mgm rear end has been whining for the last 20k miles, since I switched to 75w-140 wt and other than the noise the differential seems to be fine. According to a shop I go to a whining diff (with thicker oil) doesn't mean anything is bad or worn, Ford even had a tsb to use a 90 weight when customers complain about whining diffs. Perfect example is before I changed the diff fluid on my car the diff was silent after I changed the fluid and used 75w-140 the diff started to whine.