Front axle differential on 2000 chevy silverado leaking oil out of vent .the differential is not overfilled.

not told what leaks and to where.
we can no see leaks blind in text box.
axles?
autotrans
manual trans.

cause are only 3.
bad gaskets and seals
overfilled. (never do that)
or on ENGINE ( )PCV valve clogged and engine pushes oil out
rear main seal and to the TC and bottom bell housing leaks oil
and is not the transmission, leaking. fooling owners.
oddly
other causes, 4wd axle vents clogged with mud or bug nests>

no engine told
no transmission told at all(options day1 new car)
RWD
Front; with Mitsubishi R4A51 Transmission
or Front; with Mitsubishi V4A51 Transmission

You are likely to get an oil 'mist' from a vent or breather tube -this is quite normal. The 'mist' cools around the breather and forms a small oily patch. on the axle casing.

Are you certain that the oil is coming from the vent tube and isn't due to a split in the metal casing or from the gasket/seal?

How much oil are you losing? The only other way you would lose oil is if excess pressure was building up inside the differential and to be honest, it's difficult to see how this would occur unless it has recently been over-filled with oil.

If there are drips of oil appearing on the ground underneath the axle/differential chances are that it's the cover seal or the pinion seal at fault. The pinion seal is where the driveshaft/propshaft attaches to the differential. The cover seal is the gasket between the metal cover where the filler plug is and the differential casing itself.

Only if that is where the leak is.
Would be good to determine that before dismantling.
Leaks could be from the front seal, from the differential cover, from the fill plug, or from the vent.
Some differential covers are using sealant instead of a gasket these days.
A leak indicated from the front seal ( where the drive shaft is attached) might tell you to just keep adding oil, as it could be really expensive to fix.
God bless your efforts.

You must remove the rear cover on the differential and then the spider gears, then the center pin bolt and the pin then push in on the axle and remove C clip retainer inside the gear carrier and slide axle out.

are wheels free to move ? could be just stubborn , Is the seal holding it in ? lockring ? a repair manual would be helpful , todays vehicles have many surprises, I have one for all (4) of my vehicles, what gear is truck in ? should be neutral , yes ? you have jacks under frontend, yes. good luck

Replace the unit with a used one. Be sure to get alignment after you are finished.

The transfer case uses two types of oil one is automatic fluid the front part of differential takes gear oil 85/120 wt. both differentials I would use synthetic oil and would run 85/120 however if the rig has been well used you might want to go with a higher weight oil oil so you don't get wheel seal leaks.

Axle Vent
NOTE: If the vent cannot be cleared, it must be installed new.
A plugged vent will cause excessive seal lip wear due to internal pressure buildup. If a leak occurs, check the vent. Make sure the vent hose is not kinked. Remove the hose from the vent nipple and clear the hose of any foreign material. While the hose is removed, pass a length of mechanics wire or a small diameter Allen wrench in and out of the vent to clean it. Connect the hose when done. The vent is located on the drivers side top of axle housing.
If you plan on doing most repairs yourself I would suggest buying a Haynes or Chilton manual for your particular vehicle. Or there are some data disks on e.bay($12-$15) For a cost of under $25, you can almost do any repair yourself with these manuals.Also there are online manuals like the site called ALLDATA where guides can be viewed for a fee. All these solutions will save you time and money, and give peace of mind over correct repairs. I can post you some procedures here also.

1. CAUTION: Do not use heat to loosen a seized lug nut. Heat can damage the wheel (1007) and the rear wheel bearings (1225).
2. Loosen the lug nuts (1012).
3. Remove the center cap.
4. With the weight of the vehicle on the wheels, loosen the lug nuts Raise and support the vehicle. .Remove the wheel and tire assembly.
   
5. Remove the lug nuts.
   
6. Remove the wheel and tire assembly. Remove the axle housing cover (4033).
   
   1. Loosen the axle housing cover bolts (4346) and drain the rear axle (4001).
   1. Remove the axle housing cover bolts.
   1. Remove the axle housing cover.
   

7.Remove the rear disc brake rotors You will have to remove the brake caliper to get rotor off.
8. CAUTION: Once the differential pinion shaft (4211) has been removed, turning the differential case (4204) or an axle shaft (4234) will cause the differential pinion gears (4215) to fall out of the assembly. This could result in chipped or damaged components.
9.
1.Remove the differential pinion shaft lock bolt. 2.Remove the differential pinion shaft. 10.CAUTION: Do not damage the rubber O-rings in the U-washer grooves. Remove the U-washers (4N237).

1. Push the axle shafts inboard.
2. Remove the U-washers.

11.Reinstall the differential pinion shaft.
1. Install the differential pinion shaft.
1. Install the differential pinion shaft lock bolt finger-tight.

12.CAUTION: Do not damage the inner wheel bearing oil seal (1177). Remove the two axle shafts.

CAUTION: Never remove the axle shaft oil seal by itself. Always remove the rear wheel bearing and the axle shaft oil seal at the same time. NOTE: If the axle shaft oil seal is leaking, the axle housing vent may be plugged with debris. Use Impact Slide Hammer and Axle Wheel Bearing Puller to remove the rear wheel bearing and the axle shaft oil seal.

Axle bearing puller end..
Installation
Lubricate the lip of the inner wheel bearing oil seal.
Use Premium Long-Life Grease XG-1-C or equivalent meeting Ford specification ESA-M1C75-B.

1. CAUTION: Once the differential pinion shaft has been removed, turning the differential case or an axle shaft will cause the differential pinion gears to fall out of the assembly. This could result in chipped or damaged components.
2. Remove the differential pinion shaft.
3. Remove the differential pinion shaft lock bolt.
4. Remove the differential pinion shaft.

CAUTION: Do not damage the inner wheel bearing oil seal. Install the two axle shafts. CAUTION: Do not damage the rubber O-rings in the U-washer grooves. Install the U-washers.
1. Position the two U-washers on the button end of the axle shafts.
1. Pull the axle shafts outward.

Install the differential pinion shaft.
1. Align the hole in the differential pinion shaft with the differential pinion shaft lock bolt hole.
1. Install the differential pinion shaft lock bolt.

Install the rear disc brake rotors; Install the axle housing cover and fill the rear axle housing (4010) with 2.4 liters (5.5 pints) of specified lubricant
WARNING: Always remove any corrosion, dirt or foreign material that may be present on the mounting surfaces of the wheel or the surface of the wheel hub or rear disc brake rotor that contacts the wheel. Installing wheels without proper metal-to-metal contact at the wheel mounting surfaces can cause the lug nut to loosen and the wheel to come off while the vehicle is in motion, causing loss of control. Clean the wheel hub and mounting surfaces. Install the tire and wheel assembly.
Position the tire and wheel assembly. Install the lug nuts and lower the vehicle. Tighten the lug nuts. Install the center cap. WHEW Hope this can help you

the vent cap is to keep out water and to relieve differencial pressure. you can replace this yourself if thus is the cause of the leak for under 10 bucks.

First check level of oil in rear end housing, if low, pull drums & see if any axle seals are leaking.
If you want info on doing axle bearings, get back to us.