Front Diff Vent

[smytheman]

Anyone have an idea what would cause my front diff vent tube to spit out gear oil? The fluid level is within specs, although it is pretty murky. Could it have just been overfilled the last time it was serviced?

 

I'm planning on replacing the dino oil with synthetic; have you guys been replacing the vent connector per the GM Techlink article?

 

The truck is a 2000 Z71...Thanks.

[Black02Silverado]

Sounds like it was overserviced. I would change out the fluid with regular GL5 rated gear oil and see how that works. If that runs fine and no more oil out the vent tube then you can switch over to synthetic. Reason to use regular oil is if there is a problem no sense wasteing the expensive oil.

 

I switched over to synthetic AMSOIL and didn't change anything but the oil. No problems and that was 33k miles ago.

[JayMan]

Sounds like it was overserviced. I would change out the fluid with regular GL5 rated gear oil and see how that works. If that runs fine and no more oil out the vent tube then you can switch over to synthetic. Reason to use regular oil is if there is a problem no sense wasteing the expensive oil.

 

I switched over to synthetic AMSOIL and didn't change anything but the oil. No problems and that was 33k miles ago.

 

Good point!

 

Have you checked out the TSB database at All Data?

 

http://www.alldata.com

 

I don't recall a case of gear oil actually being pushed out a vent unless the axle was WAY overfilled. Like right up to the TOP. I've seen this happen a lot with commercial Allison automatic's that were way overfilled.

 

Another reason could be the axle is WAY overheated. If you have a very poor quality gear oil, or a gear oil that has degraded, it will run hot, especially if you're always in AUTO 4WD or if you have a Denali AWD. Dino gear oil will expand when hot, synthetic gear oil much less so.

 

I would also check to see if the vent tube is plugged or kinked. If the tube is blocked, then when hot pressure will build up in the axle and fluid may squirt out. The vent tube is wrapped to a wiring harness so use care when checking this.

 

Note: The front axle never completely runs "free" like the old ones with manual hubs. Even in 2WD, the halfshafts are still spinning and the side bearings are still turning. I hope your bearings are ok.

 

Since the fill plug is at the side of the axle, and oriented to the very front of the truck, if you happen to jack up the truck to make access easier, you WILL overfill the axle. Here is what I do:

 

I drive into my shop, which has a perfectly level cement floor. I take the skidplate off to make access easier. Take off and carefully clean the fill plug and drain plug. After draining, checking the drain plug magnet, etc, put the drain plug back on and refill. It only holds about 3.5 pints!

 

Once the oil begins to run out, let it continue to seep. I tape the fill plug to the truck keys and put the truck keys on a paper towel on the driver's leather seat.

 

I then find a way to kill 10 minutes. Like make a pot of coffee, brush the cat, etc. Then I go back to the shop, see if there is any more oil seeping out. If not, take the fill plug from the keys, roll underneath and put the fill plug and skid plate back on.

 

If you have a gear oil pump like mine that even records the volume, USE IT. 3.5 pints isn't a lot of fluid. The most important thing is to make sure the truck is sitting on a LEVEL SURFACE when checking the gear oil.

[chevroletmb]

if your front diff vent plug is black then it is not compatable with sythetic fluid

if you run synthetic gear oil there is an updated white front diff plug available from gm that is compatable

[bbb]

their is an upgraded vent available covered under warr

orig is black with a plastic inner vent

new one is white with a heavier metal vent so it will stay down

syn or reg gear oil

 

note: keep the level .5" below fill hole or the axle seals tend to leak

[JayMan]

if your front diff vent plug is black then it is not compatable with sythetic fluid

if you run synthetic gear oil there is an updated white front diff plug available from gm that is compatable

I've run commercial synthetic gear oil in my front axle from new. No problems. The local dealer is willing to give me the updated white vent plug, so next year I'll put it in.