no need whatsoever to change diff fluids unless you want to - just check the levels, with three diffs and four driveshafts etc there is always a lot of movement and clunking in high mileage 4wds. If there are drain plugs on your diffs its a five minute job then put in a fully synthetic ep oil. The brake clunking is also normal.Front and Rear Diffirential Questions?
Servicing of the front and rear axles will not correct any drive line noises. Just like changing the engine coolant, it is performed as a preventative service. Over time the axle lubricant chemically breaks down giving less protection to internal gear wear.
On you Jeep, both axle inspection covers are removed, the oil drained, covers reinstalled (they don't use gaskets, just RTV sealant) and new gear oil added. In Canadian dollars, depending on who does the service (private vrs, dealer), it would cost around $140 to $240.
I don't know how long you've owned your Jeep, but hearing some %26quot;engagement%26quot; groans-noises when you shift from drive to reverse is normal. Once it's not a LOUD type of sound.
Before spending money on the axles, you should take her to your local garage and talk with them about having your truck inspected. You might find other issues you could address first.
