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Neglected rear end diff, same as neglected tranny?

Discussion in 'GM Powertrain' started by McClintoc, Sep 8, 2012.

  1. McClintoc

    McClintoc Super Moderator Staff Member Platinum Contributor 1000 Posts

    I can't remember the last time I changed my rear diff fluid - bad, I know. The good news is, I don't tow and rarely haul with my truck. In fact, I don't even have a towing package. Therefore, my rear diff has never really been stressed so hopefully the fluid isn't "bad". The only thing is, I really think it's been close to 100,000 miles since I last changed it. So, my question is this: will it hurt to change it out since it's been that long or should I leave it be? It's a well known fact that if you haven't changed out your transmission fluid in a very long time, it's actually better to leave it at that point or the transmission will fail if you change out the fluid. Considering my siutation, will the same thing happen to my rear diff if I change out the fluid after it's been so long?
  2. tbplus10

    tbplus10 Super Moderator Staff Member Platinum Contributor 1000 Posts

    No the diff is a little different it'll appreciate the fluid change.
    Since you dont change it as often you might think about using synthetics back there.
  3. McClintoc

    McClintoc Super Moderator Staff Member Platinum Contributor 1000 Posts

    Definitely a consideration but a new question arises: they say it is bad to switch over to synthetic oil in your engine after years of using regular oil. Again, does the same rule apply to the rear diff or no?
  4. dpeter

    dpeter Member

    Who is "they" that you get your info from? I personaly think it is never to late to change your fluid and if it fails sometime after that it is due to the fact that it was failing anyway and only convenient to blame it on something other than your own neglect.
  5. McClintoc

    McClintoc Super Moderator Staff Member Platinum Contributor 1000 Posts

    I get my info from auto parts stores, general repair shops, transmission shops, etc. You know, the experts/professionals.
  6. tbplus10

    tbplus10 Super Moderator Staff Member Platinum Contributor 1000 Posts

    The big issue changing to synthetics is increased chance for leaks, all synthetics do is let you know yes I have a leak and now that I know I've gotta do something about the problem.
    Synthetics create less drag and friction one reason for this is they permeate metal and gaskets better than conventional oils, this is why after starting to use synthetics you suddenly find you have a leak, it was there all along it just wasnt as obvious.
    Look at your axle seals and, pinion seal and rear cover gasket, if they need replacing nows a good time, if their in bad shape they will start leaking anyways, might be a week after you change the fluids or it might be a year, either way they need to be changed.
  7. McClintoc

    McClintoc Super Moderator Staff Member Platinum Contributor 1000 Posts

    Thanks for the info TB. I'll more than likely have a shop change the rear diff fluid so while it's in there I'll have them replace all the seals/gaskets and then fill it with synthetic.
  8. nikkeshelton

    nikkeshelton New Member

    Oil is an organic compound so in time, heat and age will break down gear oil. Ever change out an old one and, noticed the rancid smell? Believe me, your gearbox will appreciate it!

    - - - Updated - - -

    You are right about the synthetics! I was running royal purple and the dealer put mobile one in, now I seem to have a rear seal leak!! 30,000 on the truck, and I know royal purple is synthetic also but I've had the same experience with Mobile 1 before.

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