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Gear head said not to use synthetic in diffs and this is why!!

Discussion in 'Maintenance & Upkeep' started by the phantom, Aug 7, 2012.

  1. the phantom

    the phantom Active Member 1000 Posts

    I was talking to a guy that rebuilds front and rear differentials for the past 30 years and he told me that synthetic oils are great. But not for the differentials. He said the reason why you shouldnt use it is because conventional gear oils push the contaminates to the side walls of the diff cases and it sticks there not allowing it to be continually ran through the gears and bearings. He said that he has seen bearings shot after about 50-60k miles because of this. He said that synthetic oils are the best for any system that is filtered but diffs are not. And the properties of the synthetic blends do not allow any wear contaminates to stick to the sides like the conventional oils. I guess if you continually change the oils maybe this statement may not apply. But then at what interval would be acceptable to not allow any of the contaminates to wear on the bearings ect. Just thought I would share an opinion.
  2. RayVoy

    RayVoy Active Member 1000 Posts

  3. the phantom

    the phantom Active Member 1000 Posts

    That is a lot of testing that is for sure. I guess my only thought on the tests are that it really doesnt put any of the oils through its real life scenario such as the time factor involved. If these tests could be conducted over a period of 4 and 5 years including the temperature changes in that amount of time I may lean more to agreeing that the synthetics do what they say. I think I would lean more to using synthetics in my diffs when I change my gears soon and just change the oil out often. Afterall I did buy a rear diff cover that has a drain plug in it.:great:
  4. RayVoy

    RayVoy Active Member 1000 Posts

    GM diffs (especially the front one), have a habit of picking up water, changing the fluid more often than the recommended interval is not a bad idea (unless you get it done at a GM shop).
  5. dpeter

    dpeter Member

    They push contaminates to the side walls of the diff case!!?? WTF and OMG. You know my dad had a car that only took a key to run. I know this for a FACT because I never saw him change oil or put gas in it so it had to be the key. I wonder what ever happened to that car. I think I was about four or five when it went away and then he got this truck that he was always putting gas in. How is it that old saying goes--- Believe half of what you see and none of what you hear.
  6. Pikey

    Pikey Moderator Staff Member 1000 Posts

    My gear guy said the exact same thing when I had the front and rear diffs redone on my 03 yukon xl. He runs conventional oil with a friction modifier. He refuses to put synthetic in a diff. I said "I will buy the synthetic oil to put in the diffs when you are done" He responded, "You can buy it, but there is no way in hell I will put it in, you are welcome to drain my oil out and put it in yourself, but I will not honor my warranty".
    Last edited: Nov 30, 2012
  7. RayVoy

    RayVoy Active Member 1000 Posts

    Well, there are still guys who insist on changing engine oil every 3,000 miles..........................

    .........hmmm, what did I just start:rofl:
  8. the phantom

    the phantom Active Member 1000 Posts

    So if you drain the oil out, then pull the diff cover, obviously all of the contaminates will not be suspended in air. So how do you find out how true this is. Remove the entire rearend out of the vehicle, put it on a bench and pull the cover off facing up and look inside with the oil still in it??? suck the oil out and see if the contaminates are against the walls of the housing? what prevents the contaminates from sticking to any of the other parts inside that dont move. I dont know. It sounds like a possibility that it may be true. But we could also argue that synthetics are so good that there are no wear contaminates to worry about.
  9. dpeter

    dpeter Member

    "But we could also argue that synthetics are so good that there are no wear contaminates to worry about."
    I'm going with this one:great:
  10. tbplus10

    tbplus10 Super Moderator Staff Member Platinum Contributor 1000 Posts

    When you drain the oil out if you strain it you'll find your contaminants, right in the oil, just like conventional oil.
    If this mechanics theory were true you wouldnt need a filter on your engine, all the contaminants would be stuck to the sides of the oil galleries, I've broken open quite a few engines, gear box's, and axles running Synthetics and none of them had anymore contaminants sticking to the sides than there was on parts using conventional dino oil.
    When I used to work on Jets we had huge oil pots for the main induction gearbox's that unbolted from the bottom of the gearbox that you dropped straight down then tilted to drain the oil into a bowser, we used synthetic oil for all the engine lube and after dropping over at least a 100 oil pots in a 20 year career I've never seen what that mechanic describes happen, the contaminants were always mixed in the lube.

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