1. Welcome to PlowSite. Notice a fresh look and new features? It’s now easier to share photos and videos, find popular topics fast, and enjoy expanded user profiles. If you have any questions, click HELP at the top or bottom of any page, or send an email to help@plowsite.com. We welcome your feedback.

    Dismiss Notice

Front diff blowing diff fluid out of vent tube.

Discussion in 'Chevy Trucks' started by 70monte, Feb 26, 2008.

  1. 70monte

    70monte Senior Member
    Messages: 468

    My 98 K3500 that I recently bought has been lately blowing diff fluid out of the vent tube. When I first got the truck, I checked the front diff fluid and could not feel any diff fluid through the fill hole so I filled it until a little bit started coming out the fill hole. That is when it first started doing this.

    Later I decided to change the front diff fluid. My Chilton's manual said that the front diff in this truck holds 4.4 pints. I put less than two quarts in when it started to slowly come out the fill hole. I put the plug in and left it. It says to fill the front diff so its 1/4"(I think, I can't the remember exact amount below fill hole) below the fill hole so I know its a little overfull, but I don't know how to accurately get the level the correct amount below the fill hole. When you put your finger in the hole, you can feel something sloping away.

    The front diff tube on this truck did not have the plastic vent in the end of the tube like my 98 1/2 Z71 has. I went to the dealer and got one for it. Now that I have the plastic vent in, it hasn't been able to blow out so far.

    Is it blowing out the diff fluid because I didn't have the plastic vent in the tube?

    Is it doing it because the front diff is too full? If so, will it do any damage?

    Is there something mechanically wrong? It does sound like I'm getting some noise at around 55 mph but I'm not sure if its the tires or the front diff.

    Thanks for any info.

  2. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    How much fluid does it actually push out? A lot?

    I'd start with getting it to the correct level. Pull the fill plug with the truck on level ground to let any excess drain out. That is the correct fluid level.

    The only ones I've ever seen push fluid out is if they're grossly over full or if the diff is stuck "engaged" for long periods of time and operated at highway speeds.
  3. 70monte

    70monte Senior Member
    Messages: 468

    Its kind of hard to tell how much its actually pushing out since the fluid is sprayed in different places. The truck was on a level concrete carport when I filled the diff. Not very much fluid seemed to come out the fill hole when I first filled it. I will take the fill drain plug out and let whatever can, come out.

    The front diff doesn't seem to be engaged since nothing seems to be binding when turning on dry roads and the light on the 4x4 shifter on the floor is not lit. Thanks for the help.

  4. 70monte

    70monte Senior Member
    Messages: 468

    I finally had time to mess with the truck yesterday and took out the fill plug. Nothing came out, even after letting it sit for awhile. I guess the excess was blown out of the vent tube. I will just drive it and see what happens.

  5. Spitz

    Spitz Senior Member
    Messages: 192

    Did you happen to put synthetic in the diff?? Sometimes certain synthetics will foam a lot more then one would expect..
  6. 70monte

    70monte Senior Member
    Messages: 468

    I didn't use synthetic in it. I used 80W-90 Rotella heavy duty in both front and rear diffs.

  7. 350-CHEVY

    350-CHEVY Member
    Messages: 81

    i've had that happen to my truck as well and when i put the vent tube on it, it stopped spraying out. i think its cause the oil can leak out easier with no tube