Rear Main Leaking

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by odfraire92, Oct 23, 2020.

  1. odfraire92

    odfraire92 Bobtail Member

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    I have a 2011 Prostar with a Cummins that has 1,185,000 miles with around 25,000 since I had an inframe done and a 10 speed transmission. 2 years ago I changed the rear main seal after it had been leaking for a few months. A couple of months later it started leaking again and got it replaced again (with a different mechanic). Was good for a few months and started leaking again. Been running like that for about a year now and getting ready to replace for the third time now. Any ideas why the seal keeps giving out? Or is it mechanic error? Thanks in advance!
     
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  3. Goodysnap

    Goodysnap Road Train Member

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    Measure crankshaft endplay.

    Since the seal has been done many times, throughly inspect the housing and crankshaft for nics or burs/damage that may have resulted from the seal replacement.

    Adding oil dye can help to pin point the leak further, say in case the oil is not actually coming from the crank seal, but from somewhere else inside the flywheel housing.
     
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  4. odfraire92

    odfraire92 Bobtail Member

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    Oct 17, 2016
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    Say there is nics or scratches would I be able to sand it down a little or have to replace more parts?
     
  5. Goodysnap

    Goodysnap Road Train Member

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    Depends on the severity of the damage. Tool groups to remove the seals use drilling and screws, so damage due to misuse is somewhat commonplace.

    I have filled minor nicks with JB weld and finish sanded smooth with good results. The key is no high spots to cut or gouge the seal on install because you are literally pressing it in.

    Takes attention to detail and patience, but can be done.

     
  6. AModelCat

    AModelCat Road Train Member

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    From what I've seen, an incorrectly installed main seal usually starts leaking pretty quickly after install.

    Excessive crankcase pressure can cause the front and rear mainseals to blow as well.
     
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