DIY: Differential Fluid Change- Advanced (RC only)

Discussion in 'How-To/Tech Database' started by Kevan, Jan 30, 2008.

  1. Kevan

    Kevan SRT-10 Owner

    Likes Received:
    Dec 15, 2007
    New Albany, OH

    Here's a shot of the tools we'll need:
    • Oil catch pan
    • 3/8" drive socket wrench
    • 1/2" drive socket wrench
    • 9/16 socket (3/8" drive)
    • 18mm socket (1/2" drive)
    • 4" extension (3/8" drive)
    • 8" extension (3/8" drive)
    • Torque wrench (ft. lbs.)
    • X-acto blade
    • Wire tube brush (aluminum or brass bristles)
    • Wire cutters (for opening diff. fluid bottle nozzles)
    • Quick-clamp in spreader mode
    • Chip brush
    • Delrin "scraper"
    • Plastic bristle brush
    • Drill driver w/ 3/8" adapter
    • Pump with hoses
    And here are the supplies needed:
    • (3) quarts of differential fluid (your choice)
    • (1) 4 oz. tube of Limited Slip Additive
    • (1) tube of silicone sealant (the black tube)
    • (1) tube of thread sealant (the gray tube)
    • (1) roll of paper towels (or shop rags)
    First, remove the spare. You'll need as much room as possible under there.
    Next, we need to setup the truck for proper drainage. At the very least, it should be on a level surface. If you can, ramp up or jack up the front of the truck. This will help remove ALL of the differential fluid as gravity usually wins.

    Now, before we take the cover off, we need to take the linear shock off the cover. It's far easier to remove the shock than it is to take the shock mount off the housing.
    Here I use the quick-clamp as a spreader to keep pressure on the shock:

    Then remove it's mount bolt:

    Use a bungee cord or zip-tie to hold the shock upward and out of your way as you work under there.

    Place your drain pan under the differential. Make sure you have enough room to spare because the fluid isn't going to drip- it's going to flow quite heavily, like pouring milk out of a carton:

    Using your 3/8" socket wrench and the extension, carefully remove the drain plug located at the bottom of the diff. cover:

    You'll notice that the fluid begins to slowly flow out:

    Keep unthreading the plug, and enjoy the flow:

    Be careful as you remove each plug because they both have a magnetized tip. This magnet collects the small chips (swarf) and other nasty bits that would cause damage to your differential. Here's the bottom drain plug with all sorts of crap on it:

    And here's the top fill plug, again with more crap on it:
    If you so desire, you can save this swarf and have it analyzed or simply wipe it away. Before re-inserting either plug, make sure the magnetic tips are clean.

    Here we have both plugs out, to allow plenty of air in the top so fluid can come out the bottom:

    Now, go watch the latest release from Krystal Steal and wait for the fluid to fully drain. As this is very thick 'oil', it will take a decent amount of time for it all to come out.

    After "a while", I proceed to remove the differential cover. I loosened all of the cover bolts with the regular socket wrench, then moved onto the power tools. :D
    The drill really does speed things up.

    When the cover bolts are off, you will need to tap the sides of the cover with your fist to shock the silicone sealant enough for it to break loose. Keep a hand ready as the cover will come loose quickly. I grabbed ahold of the shock mount and wiggled it a bit while holding onto the bottom at the same time...and the cover came right off, and into my left hand.

    Here's what it looks like sans cover:

    As you can see, the diff. is still draining:

    Go enjoy an adult beverage while it finishes up.
    Check the air pressure in your tires.
    Windex the windows (inside and out).
    Now go back and wipe the front face of the diff. and check to see if it's still flowing. If yes, find more stuff to do. If no, then move on to the next step.

    Here's the inside of the diff. cover:
    Not too bad, but we'll need to clean it out. After cleaning, make sure there's no lint, paper towel bits, etc. inside or on the face.
    Clean out the plug holes too.

    On the faces of the diff. housing and the diff. cover, you'll notice a thin layer of silicone. THIS MUST BE REMOVED!
    On the diff. housing, be extra careful not to let any chunks of old silicone enter the housing. I hold a shop towel in my hand and "palm" the exposed gears as I use a piece of plastic (Delrin, actually) to scrape away all the old material.
    Do this on both the diff. housing *AND* on the diff. cover.
    Make sure all that material is GONE. Clean the surfaces with acetone. Twice. If the paper/shop towel comes back white, it's clean.

    The hardest part about this whole thing is the damn silicone in the mounting screw holes. I tried several methods before doing it like this:
    Trim out the old silicone with an X-acto blade:
    Note the plug holes filled with paper towels to absorb the gear fluid in those holes/threads.

    Take your time and be careful not to take chunks out of the aluminum housing with the steel blade of your X-acto blade.

    You won't be able to get all the old silicone out of the holes with the knife, so I used a small wire brush/tube/pipe cleaner to finish off the holes.
    This particular one has steel bristles, but they were mal-formed during another project so they were a perfect size to fit the holes (and didn't mess up the aluminum). I recommend using an aluminum or brass bristle brush instead of the steel I used.
    Don't forget to clean off the silicone from the bolt hole areas on the outer face too!

    Take your diff. cover bolts and using a plastic or brass brush, clean the threads. They need to be clear of silicone and dirt as well.

    So, now we have a clean cover (including the mating face and plug holes), and we're ready to put it back on the truck.

    Go back and make sure all the fluid is out of the differential. Use a paper towel as a 'sponge' and set it on the bottom edge to soak up the remaining fluid inside. We don't want it to drip down as we put the new seal on there. That would suck.

    When your sponge is soaking, apply a nice bead of the new silicone w/sealant around the center of the diff. cover. Some like to do "U-shapes" around the bolt holes. I'm far more anal. :)
    Here's what your bead should look like:
    Now, you've only got about 10 minutes to get this thing on there before your silicone is too dry to use. Make sure you've got everything ready.

    Check to make sure the diff. housing face is clean and free of old silicone and apply the diff cover onto the housing *slightly* out of alignment. I do this so the silicone spreads a little as it gets mounted.
    Re-install the bolts finger-tight. We'll crank 'em down in a minute.
    Once all the bolts are back in the cover, use your drill driver and quickly cross-bolt the cover bolts nice and snug:

    You should see a small bead of silicone squeeze out from the edge of the cover, all the way around the edge of the cover:
    Some like to just wipe this away while the silicone is wet. I've found that while this works, it can also be a huge mess. I'm going to do it differently (more on that later).

    Then use the torque wrench and finish them off (cross-bolt pattern as well):
    Torque the diff. cover bolts to 35 ft. lbs.

    Apply some silicone thread sealant to the threads on the drain plug (top to bottom), and install the drain plug:

    Torque the drain plug down to 20 ft. lbs.:
    Some sealant may bead up along the outer edge. Leave it alone and let it dry. We'll clean it up later.

    Before we re-fill with the new fluid, we should let the new silicone sealant fully cure. This is normally 8-24 hours (check the label on the silicone sealant you use). At the very, very, VERY minimum, you should let the silicone dry for 2 hours before introducing any diff. fluid into the housing.

    When the silicone is try, you'll have a rubbery bead all the way around the diff. cover. Since the mating parts are machined, they make an excellent edge, and will cut that dry silicone with a little bit of back/forth motion.
    Using your fingers, do this all the way around the diff. cover.

    When you're finished, you should have a nice clean joint between the housing and the cover, with little or no extra silicone hangin' over their edges. Like this:

    Now that the silicone is fully cured, we're ready to add fluid. First thing to do is lower the front end of the truck. Make sure it's as level as possible. If the nose is up at all, you won't put in enough fluid; if the nose is down, you may add too much fluid and blow out seals or cause other damage.
    When you're level, add the Limited Slip Additive (aka LSA). This comes in a 4 oz. tube, so you want to add all of it.
    Keep your drip pan under the diff. cover just in case any slips out.

    Some folks like to pour right from the bottle into the diff. If that's you, and you're using Mobil 1 fluid, remove the paper seal under the nozzle:
    You don't want to know how I found out about that. :)

    Some folks (like me) prefer to use the pump:
    $10 at most auto stores or Wal-Mart. Worth every penny.
    Make sure your tube goes into the diff. housing and *stays* in there as you're filling up.

    The manual says "3.5 qts." of fluid for the diff. Mine was full at exactly 3 qts. You'll know when it's full when the new fluid starts to drip out of the bottom edge of the fill hole:

    Apply thread sealant (top to bottom) on the fill plug and put it back in the diff. cover:

    Torque the fill plug to 20 ft. lbs.:
    Again, we'll have some of the thread sealant bead up on the outside. That's fine, leave it for now. We'll come back to it once it's dry.

    Use a shop rag or paper towel and clean up any fluid that might have dripped down from the fill hole. We'll need it clean for the upcoming seal check.

    After wiping down the diff. cover thoroughly, lay down a clean paper towel and place it under the differential. This will tell you if you have any leaks.
    After 4 hours:

    After 8 hours:
    Looks good.

    Now is a good time to get rid of that extra thread sealant. You can use your X-acto blade and trace around the edge, or simply wipe it away.

    With the cover back on and everything torqued (and re-torqued after the silicone dried), we can put our linear shock back on. Use the quick-clamp spreader to hold the shock in place as you line up it's mounting bolt:

    Insert the bolt and re-attach the nut for the shock mount. Using the 1/2" socket wrench, get it as tight as you can:

    Then torque it to 75 ft. lbs.

    It's time to take it for a drive around the block. You should notice that when in gear and off the throttle, the truck is smoother as it rev's down. That's your new fluid doing it's job!

    After the test drive, come back and put another clean paper towel down under the differential and let it sit overnight (use a wrench to hold it in place). Check for any leaks.

    There ya go! Your differential fluid has been changed and ready for another few thousand miles.

    Last edited: Oct 22, 2008