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Rear end oil, synthetic in an oil dog leg

Discussion in 'The Hokey Ass Message Board' started by Roothawg, Mar 1, 2014.

  1. Roothawg
    Joined: Mar 14, 2001
    Posts: 20,456

    Roothawg
    Member

    Just got through cleaning the Wagon rear differential and housing, going back together with new axle seals and bearings.
    Thinking this might be time to take advantage in technology advancements and pick up an extra freebie in the mileage dept.

    I'm just a little leery that I may create a pinion seal leak.
    Is there enough gains from the synthetic to warrant the extra expense?
    I will be towing the Fly and our vintage travel trailer.

    It's a 10 bolt Chevy rear end, non posi .
     
  2. trbomax
    Joined: Apr 19, 2012
    Posts: 289

    trbomax
    Member

    Ive run synthetic fluids ina all my vehicles,my OT ford SD has had it since new in both diffs with 190k on it now,has never leaked a drop. The storys about synthetic leaking more than dino are IMO a load of crap. On the other hand, the only good reason to run it in a diff or trans is if you are towing and heat buildup is an issue. Synthetics hold up far better than dino in high heat/load conditions.
     
  3. brokenspoke
    Joined: Jul 26, 2005
    Posts: 2,890

    brokenspoke
    Member

    I think the only time synthetic is a problem leaking is with cork gaskets....????
     
  4. oldsjoe
    Joined: May 2, 2011
    Posts: 2,528

    oldsjoe
    Member

    Interesting I have the same question. I'm working on a mid 60s open single track Olds rear.
     

  5. Twenty years ago changing to a synthetic oil was a problem with seal leaks. Today synthetics can be mixed or changed to without harm to gaskets or components. The big worry is with anti wear additives or the lack there of due to the reduction of these additives to protect the precious metals use in catalytic converters.
     
  6. Roothawg
    Joined: Mar 14, 2001
    Posts: 20,456

    Roothawg
    Member

    I run synthetic in all my cars, however they all leak. Coincidence ? Maybe, all my cars have 135k and up......

    All the seals are new except the pinion seal and it shows no signs of leakage.
     
    Last edited: Mar 1, 2014
  7. joel
    Joined: Oct 10, 2009
    Posts: 1,777

    joel
    ALLIANCE MEMBER

    Synthetic won't cause a leak, but if you have a small leak, synthetic will usually find it.
    I run synthetic in all my stuff, except the rear in my 40; it has an Auburn posi and they say not to.
     
  8. stimpy
    Joined: Apr 16, 2006
    Posts: 3,547

    stimpy

    if synth find a leak the seal needed to be replaced anyways is how I look at it . it runs cooler and lasts longer . but smells the same ...:(

    and I have changed mineral oil gear oil out on 25 year old /500-750K mile semi trucks that was mineral based to synthetics and never had a leak issue , and that a heavy load and high temp use .
     
  9. Roothawg
    Joined: Mar 14, 2001
    Posts: 20,456

    Roothawg
    Member

    I'm gonna try it and see what happens.
     
  10. oldsjoe
    Joined: May 2, 2011
    Posts: 2,528

    oldsjoe
    Member

    I'm replacing ALL THE SEALS and GASKETS with ALL NEW BEARINGS so I'm leaning towards the synthetic too. But the old mineral based 90w lasted over 100,000 with no issues!
     
  11. Roothawg
    Joined: Mar 14, 2001
    Posts: 20,456

    Roothawg
    Member

    True, I'm just looking to maximize my mpg when towing long trips.
     
  12. saltflats
    Joined: Aug 14, 2007
    Posts: 10,393

    saltflats
    Member
    from Missouri

    I had changed the gear oil in a OT car for my brother and he notice an improvement in mpg.
     
  13. junkyardjeff
    Joined: Jul 23, 2005
    Posts: 7,673

    junkyardjeff
    Member

    The next time I have a rear end part I will try synthetic lube.
     
  14. dorf
    Joined: Dec 5, 2008
    Posts: 1,087

    dorf
    Member
    from ohio

    i put it in the rear end (CHEVY) in my 38 leaked some thing awful . took it out put the regular stuff in no leaks. so it is not bs .
     
  15. Polish the gear set. Supposed to make a huge difference
     
  16. Russco
    Joined: Nov 27, 2005
    Posts: 4,132

    Russco
    Member
    from Central IL

    I just got a new 9" chunk from quick performance in Iowa with a Trutrac posi. They specifically stated No Synthetic lube. I'm wondering if it has something to do with the gear set initial break in.
     
  17. tiredford
    Joined: Apr 6, 2009
    Posts: 500

    tiredford
    Member
    from Mo.

    I just changed gear oil in my F100. Almost all the oil they had was syn. They had a couple of off brand qts of dino but I needed 3. They said they would probably phase it out because most people want syn.
     
  18. stimpy
    Joined: Apr 16, 2006
    Posts: 3,547

    stimpy

    since there is no real bearings inside the unit , I would say its more of a clinging /cushioning effect the mineral oil has vs the synthetic . synthetics drain off quickly .
     
  19. oldsjoe
    Joined: May 2, 2011
    Posts: 2,528

    oldsjoe
    Member

    So mineral based is better in your opinion for the differential? I'm trying to figure out the best lube myself the more you read the more you wonder?
     
  20. XWYNNSGUY
    Joined: Dec 7, 2008
    Posts: 103

    XWYNNSGUY
    Member

    Hey









    Hey Roothawg, I don't think that you'll ever work that rear hard enough to justify the extra cost of synthetic gear lube. The wider viscosity synthetics were developed for the almighty MPG numbers for the manufacturers. And to squeak out a little extra fuel mileage for the long haul guys. And remember they can call it a semi synthetic and its still 99.5 % conventional. And it will be quieter with plane old 80/90 in her. Good luck !!!
     
  21. Roothawg
    Joined: Mar 14, 2001
    Posts: 20,456

    Roothawg
    Member


    Good point.
     
  22. stimpy
    Joined: Apr 16, 2006
    Posts: 3,547

    stimpy

    if you seen how that difs ( tru track) made , you see why , as for a hypoid its sliding faces you want to lube and synthetic will not break down as fast as the molecule chain will not get torn apart and not sticking to the surface will allow a better cooling of the part . and also will lower windage loss

    he has a point , only reason why OEms use it is for the CAFE STANDARDS , as thye have to sell the vehicle in the form it was tested in , and they look over the average of the total MY sold , not just one .

    on the semis , we do see the improvements as we check our MPG down to the very minimum ammounts considering the milage we drive a year is 100-150K , and I can say the rear end temps do drop 10-15* but you do not pull a 45K load .
     
  23. oldsjoe
    Joined: May 2, 2011
    Posts: 2,528

    oldsjoe
    Member

    SORRY! Didn't want to hijack your thread Roothawg but I am very curious myself I'm just going to go back with mineral based 90w hey it lasted over 100,000 miles so it should last till I'm gone! HA HA
     

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