Do i've to use brake cleaner when changing the rear diff fluid, is there a drain plug? Can i mix 80 -w90 with 85 - w 140?
I hear a clunking noise when i lift my foot off the gas pedal above 45 km/ hr and it disappears as soon as i press the pedal again. What is happening and will an oil chage stop it??? Thanks in advance.

 

Factory covers don't have drain plugs, only a fill plug. Don't mix viscosities. You can spray brake cleaner in there if you'd like. Clunking is often worn u-joints or splines in the driveshaft that need to be greased. You have to remove the driveshaft to grease the splines.

 

Better quality differential covers have drain plugs built-in for ease of changing without removing the cover. I change mine often and have them on both of mine for quick changes and inspections of fluids.

 

To elaborate further. If the jeep is a DD, a good quality oil is sufficient for a good while. Open up the diff cover, over a lube locker gasket, IMHO worth the money, and clean down with brake cleaner, close and re fill. 75(80)-90 for normal diff. 75(80)-140 for a towing rig. Don't mix oil. If you go off-road often and water crossings, use a cheAper low cost oil since you'll be changing it every water crossing providing the wTer goes above the axles. I know this all seems in organized how I typed it but I'm a few beers in. As for the clunk, that's probably the u joints. Also give more details of your jeep. Year. Lift?. DrivetrAin etc

 

Thank you so much for your replies, i have a cherokee sport 2001, automatic transmission, 8.25" chrysler rear diff. And 2" lift kit (fox dampers and oldman coil springs), wheel spacers, 255x75 tyres. Can i identify a worn u joint from its shape? And do i have to disassemble the rear diff to grease the splines?. Shall i wash the brake cleaner with some of the new oil?

 

Lube locker is overpriced for what it is. I use Fel Pro gaskets instead of RTV. They are always in stock at Advance, Auto Zone for $3.99. Greasing the splines requires removing the driveshaft, and does not require opening up the differential at all. For u-joints you basically hold both sides of the driveshaft on each side of the u-joints and twist back and forth and see if there is slop in the joint.

 

Thanks alot

 

When the cover is off, be sure to wipe with a rag the inside of the bottom of the diff case, that's where fine metal particles/crud settle.

 

Use full synthetic oil.
It's worth every penny.

 

Not really in an off road XJ where you change it often if its used.

 

I've checked the u joints both joints for both shafts and they were ok. I hope the oil change would solve the problem. I opened the fill plug yesterday after a long trip and i've found bubbles and foam in the fluid. The fluid was pale green and smelly. I haven't changed the fluid yet.

 

It's not uncommon for fluid to be slightly yellow or green. Gear oil should stink.

Synthetic 75w-140 is specified for heavy duty use.

If you aren't crossing streams or breaking axles all the time its unlikely you need to change the fluid that often. I change mine every 30,000 mostly because I like to pull the cover and look inside.

 

At the beginning of a trip when the car is cool the sound is barely heard. But after a while the sound starts to get louder at the same speed range. How can i grease the splines? Should i have a greaser or apply the grease by hand and what ammount shall i use? And shall i grease before or after fluid change? If i opened the diff cover do i still have to remove the drive shaft to grease the splines? Thanks alot for your kind help

 

Why would it require synthetic? Both my jeeps have always ran regular gear oil no premature gear wear at all. Sure if it makes you feel better put synthetic in...

 

Greasing the splines usually fixes clunks when starting or stopping. I use an acid brush and just brush through all the splines using grease out of a 1 pound tub you can get at any parts store for a couple of bucks.

The noise you are describing sounds more like some type of bearing failure.