front differential leak

mikebooms · January 3, 2007

i have a 1998 tahoe 4wd that is leaking gear oil out of the front differential breather tube that extends up near the top of the radiator on the drivers side of the truck. some days worse than others, but it leaks quite a bit. it happened twice before this in the last 3 yrs, but it would stop once i refilled it. this time no luck, refilled it twice, still coming out.

citydriver · January 3, 2007

That's a heck of a long way up for gear lube to go

The vent is there to allow for air to escape as the components heat up and expand, so that pressure does not build up and cause seal failure. Is the front differential overfilled? The fluid level should generally be below the vent line. Is the vent hose kinked or clogged anywhere? Just a couple of things I would check for 1st.

mikebooms · January 3, 2007

That's a heck of a long way up for gear lube to go
The vent is there to allow for air to escape as the components heat up and expand, so that pressure does not build up and cause seal failure. Is the front differential overfilled? The fluid level should generally be below the vent line. Is the vent hose kinked or clogged anywhere? Just a couple of things I would check for 1st.

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can only fill to the bottom of the fill hole, then it starts to come out. which is what we did. someone mentioned to me moisture in the rear will expand the fluid, is this possible? 3 people looked at this in the last 2 weeks, none have seen this before, and all of them have no idea.

citydriver · January 4, 2007

can only fill to the bottom of the fill hole, then it starts to come out. which is what we did. someone mentioned to me moisture in the rear will expand the fluid, is this possible? 3 people looked at this in the last 2 weeks, none have seen this before, and all of them have no idea.

It may be possible, but I haven't seen that before either. My gut feeling is that if there is that much moisture displacing the gear lube, bearing failure would result.

Have you tried doing a fluid change, instead of just adding lube? If not, that would be my next move if I were in your shoes. And while you're under there, double check the vent hose to make sure it's not kinked or clogged. Also make sure the drain pan you use is clean before you drain the diff. so that you have a better chance of seeing if there are any metal shavings or moisture(water) in the old fluid.

seabeeUT · May 25, 2007

Discovered this problem with a 2001 Suburban. Found that the vent hose connector had an issue that you cannot see until you remove it. If you still have this leak, or if anyone has a front differential vent leak where fluid is blown out of the vent, perform the following:

Apply the park brake.
Place the transmission in NEUTRAL.
Raise the vehicle. Refer to Vehicle Lifting.
Remove the left tire and wheel assembly.
Disconnect the vent hose from the vent hose connector.
Remove the vent hose connector from the differential carrier assembly. (24mm)
Rotate the propeller shaft until the differential case window can be seen through the vent hose connector opening.
2. Place the alignment arm of the vent hose connector in the 6 o'clock position. Caution: Refer to Fastener Notice in Service Precautions.
3. Install the vent hose connector with the alignment arm in the 6 o'clock position into the vent hose connector opening.

- Tighten the vent hose connector to 25 Nm (18 ft. lbs.)
  1. Connect the vent hose to the vent hose connector.
  2. Install the left tire and wheel assembly.
  3. Lower the vehicle.
  4. Place the transmission in PARK.
  5. Release the park brake.

Be sure to replace any missing fluid to just below the fill hole. It does NOT need to be filled to over flowing.

There is a ratcheting cap on the inside of the cover and it may, for some reason (presumably poor installation) rotate to a position where it flips over and collects fluid. Once the pressure rises in the case, it blows out the fluid. The cycle continues until enough fluid is blown out that it can no longer be slung up to the vent.

The above removal and re-assembly instructions are taken from Alldata/GM Dealerworld.

Hope this helps.

Mark

Rolling · May 29, 2007

I mentioned this in a different thread, if you replace the breather connector (the 2 inch-ish plastic plug in the side of the diff) with the new one from GM, the vent adapter inside is made of metal and will not allow itself to be rotated upsidedown, and will help keep fluid out of the vent.