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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. steved

    steved Former Member


    Gear oil is fairly stout stuff...in a car, that doesn't tow; it would probably last a long time. Until I got into the 3/4 ton trucks and diesel scene, I never touched differentials unless I was rebuilding one. Some differentials don't even have a scheduled fluid change interval.

    But when you start to add a lot of HP/TQ, weight, heavy trailers, etc. and it starts getting stressed.
  2. BoneHead

    BoneHead Member


    Thanks for pointing that out. I never thought of it from that perspective. Very helpful.
  3. Sawfish

    Sawfish Member

    I have four vehicles that we bought new, and have had synthetic oil/lube in the engines, transmissions, transfer cases and differentials since Valvoline synthetic lubricants became readily available (early 90's). 2005 Dodge Dakota 4.7L full time 4WD 86,000 miles (Chrysler ATF); 2000 Ford Mustang 3.8L 63,000 miles; 1993 2500 Suburban 4 x 4 171,000 miles; 1985 Jeep CJ-8 Scrambler 4.3L 131,000 miles. Never had to replace a gear, bearing, etc., and all transmissions and engines are original. Everyone has their opinions, but this is ample testing for me. I will stick with what works.
  4. Marcus A.

    Marcus A. Rockstar

    contaminants are usually metal particles correct. If a small magntet was placed in the cover would it not attract the particles to it removing them from the oil. Even a magnet on the outside of the case would work as long as its not knocked off. I am getting ready to change my diff oil in my '03 2500 Suburban. Factory has syn. in the rear and conv. in the front. I got free conv. for the front or I would have bought syn. for it. Need to buy syn. for the rear. I found a product called Militec-1. Started using it in chain saws, engines, trans, fishing reels. I do not recomend it for fishing reels. My bait caster spool spun so fast I constantly got back lashes(spool turns faster than the amount of line coming off). Really seems to work great. Putting it into my diffs. I also going to try a magnet on the outside of the case. Reason being, when I drain it I can remove the magnet allowing the particles to re enter the oil and be flushed out. Kinda like an electric magnet, turn off the juice and drop the metal. If I put this near the drain plug it should be picked up quickly and removed. I run syn. in all I have. Better fuel mpg
  5. RayVoy

    RayVoy Well-Known Member 2 Years 1000 Posts

    I can't tell if your talking about adding this product to the gear oil, or using it instead of the gear oil??????

    I see no advantage in adding it to synthetic gear oil, and I susgest, it would not have the sear strength to be used alone as gear lub.
  6. The Heater

    The Heater Member 2 Years 100 Posts

    If you periodically change your oil in your differential, does this argument about synthetic versus dinosaur oils really have any relevance?

    If there were some concern about the contaminants not sticking to the sides of the case and just floating around in there, if you changed the oil frequently enough then what difference would it make if you had synthetic in there? On the other hand, if you change the oil frequently then I really can't justify the extra cost of using a synthetic oil in my differential.

    So..... I use full synthetic oil in my engine. In the rest of my rig I run whatever Blood Enterprises (the repair shop I use) chooses to put in the unit. Regarding the differential, I just don't know how else to think this one through. I think I could choose synthetic or dinosaur oil for it, and I come out the same either way, so why not use the less expensive dinosaur oil?
  7. Marcus A.

    Marcus A. Rockstar

    Militec-1 is a metal conditioner, not an oil additive. Its cannot be used as an oil. For a full description you would need to look at their web site. In short, it just uses whatever oil its put into to transport it through the oil system be it engine or rear end. The Militec-1 will bond with the metal at around 140 Degrees F. and will create a thin "hardened" surface resulting in less friction. I am not selling or promoting this stuff but I've tryed it and it works. My 5hp gas air compressor in my work van starts easier and pumpsup faster and smoother since I added to the engine and compressor. Its a bit on the expensive side but I like it enough to buy more. You don't have to use it. Just thought I'd share my experiance.
  8. steved

    steved Former Member


    Almost every differential I have ever opened had a magnet attached to the inside of the cover, or a magnetic plug...unless you pull the cover, most don't even know its in there.
  9. Marcus A.

    Marcus A. Rockstar

    Correct, almost all diffs have a magnet on the plug. They are small and can only hold so much. Just changed my front diff and it was covered. I am a forklift mechanic and am constantly changing diff oil in lifts. The magnets are usually covered too. My truck will most likely never get changed again. adding a magnet may benifit me. Front diff is aluminum, so I don't know how I will do it yet. The rear could have it stuck anywhere. Putting it on the inside would be best but the chance of it coming loose and creating problems is too high
  10. steved

    steved Former Member


    Again, every differential I have serviced has had a magnet...even though some aren't external. Some are physically attached to the inside of the differential cover, others are integral to the drain/fill plug.

    And further, just how much material is your differential shedding? The initial change is typically loaded because of break in, but those changes afterwards should be almost debris free? That's been my experience with every car/truck I have owned. It can only shed so much material before it fails...

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