Mechanic says front and possibly rear differential is leaking

just why do you come here when you have a mechanic to listen too???he told you they were leaking,,,if i told you that you can run it for a week and then it breaks down tommorrow,whos fault is that???,not mine

Most rear differentials, it's a drain and refill operation.

SOME differentials have a drain plug, but others have ONLY a fill plug.

If yours doesn't have a drain plug, then you need to suck the old fluid out, with suction/transfer pump:

http://www.harborfreight.com/gear-oil-and-fluid-pump-61746.html

You can also use this to refill with the new fluid.

Most rear ends are filled to the bottom of the fill plug hole.
If you overfill, just let it overflow/drain until it stops dripping.

Now, different differentials require different fluids, so check what you need.
It might be in the owner's manual.

You need to take out the bolts holding the cover on but leave 2 in it one on eather side then pop it open with a flat head screw driver make sure u got an oil pan under it first . Then replace your gasket and put the cover back on, as for filling it there is a bolt on the front side of the axle and its usually a square hole that a 3/8 drive rachet will fit in u stick the rachet in it and take it out. Then you fill it up with the suggested gear oil and the specified amount.

Have you serviced the front differential? If you check your manual, you'll see it needs to be serviced at somewhere around 30K mi intervals similar to the transmission. Typically changing of the fluid is done but if left unchecked provides the potential for early failure.

Grinding noises from the front dif are NOT a good sign - and may indicate the need for an expensive repair / replacement. Fluids may have leaked out completely or are too low and caused overheating, etc.

I would bring it to a trusted mechanic ASAP to see if damage can be minimized!

When a pinion seal leaks gear oil, dirt usually gets inside the gear case. The first bearing to get damaged is at the front of the pinion shaft. It's a standard practice to inspect it [ if any damage is noted, then investigate further ] when replacing the seal and change the gear lube as it's usually contaimiated. Another item is the tightness of the retaining nut on the front of the shaft which sets the pre-load on the pinion bearings, if this is set too tight it will cause the bearings to fail.
Sometimes the seal is just replaced without looking at anything, you should ask your mechanic.
Chances are there's a bearing failing, it will or has caused extensive damage. You Should have it checked ASAP.

wow sorry about that. well there is no grease or quick fix for that, the pinion seal will have to be replaced. with the drive shaft removed you can remove the nut holding the yoke to the pinion gear (rear end) ,pop out the old seal and drive in the new seal, then reinstall the yoke and torque down the nut and reinstall the drive shaft. fluid loss while replacing the seal should be minimal but if you do lose fluid you may need to refill.

put flat pan under the housing remove the bolts holding the cover usually 10 or 12 (1/2 or #12 metric) bolts? allow the rear end grease to drain... then scape off the old gasket clean with brake cleaner spray install either new gasket or form one with oil resistant silicone put the cover back on , dont refill the fliud for at least 12 hours if using silicone. Also check the front driveshaft rear end yoke seal....they sometimes leak making the illusion of a rear end pan cover leak...if that is leaking you remove the shaft carefully...remove the large yoke retaining nut, replace the press in seal...be sure retaining yoke nut is properly torqued when reinstalling .

I own an 02' Jeep Liberty. It is either the differential, or the drive shaft.
Is it the front or rear driveshaft? Does the Jeep drive? If the driveshaft
was bad, it wouldn't move, so I'm assuming he's screwing you,since driveshafts don't smoke.LOL. If your front or rearend lube has come all
out or very low, you could get smoking from the diffs,especially if the fluid hit's your exhaust. look under the jeep, to see if any fluid is leaking
from the front or rear driveshafts?good luck.

no big deal if it is the inspection plate on the rear,
just removal of the ring of bolts,a pan to drain fluid in,clean both surfaces and install new gasket,refill with 90wt gear oil.

Differentials are typically filled up to the hole where the fluid is poured into. Simply fill until you see the oil starting to come out of the same fill hole... but do it slowly... don't want to make a mess.