Can we talk about the Detroit Bull Gear?

Discussion in 'Trucks [ Eighteen Wheelers ]' started by Hanadarko, Mar 27, 2012.

  1. Gear head

    Gear head Medium Load Member

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    When a bullgear is getting bad when you turn on the a/c It will ratttttle and clang and there are alot of problems with the bearings in the bullgear.:biggrin_2558:
     
    BoxCarKidd and Hanadarko Thank this.
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  3. Hanadarko

    Hanadarko Independent Owner/Operator

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    This is good to know. The last rattle I got out of the AC was the compressor itself. It sounded like marbles in a garbage disposer. I have replaced that dam thing 2x now over 3yrs....2nd one, KW installed and used the wrong bolts (too long) and cracked it just slightly...until it eventually split.

    :biggrin_25521:

    -JD
     
  4. Boardhauler

    Boardhauler Road Train Member

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    Is this a problem with the 14 liter or just the 12.7's?
     
  5. Gear head

    Gear head Medium Load Member

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  6. catmechanic07

    catmechanic07 Bobtail Member

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    Are you kidding me? Bull gears are "bullet proof"? HAHAHA!

    Here's the deal: You replace just bearings, your on your own! End of story. You buy a reman bull gear assembly, you SHOULD have dealer backing if they install. The bull gear can be installed in 1 day if they have competent tech's.

    Easiest way: Remove radiator. Remove fan hub, acc drive, cam gear cover, damper and pulley. You SHOULD remove the oil pan so you have something solid to put a bottle jack against to raise the engine. If you don't want to, good luck and remove the front 2 bolts that go into the front cover. Remove the bolts for the front engine mount. Raise the engine just enough to clear the engine mount for removal. Remove the front mount. Now is a good time to remove the front seal. Its a royal pain to pull the front cover with the seal in. Remove all bolts in the front cover including 2 that hold the water pump on and the stud for the air compressor (there may be a bolt on the compressor towards the block as well. Pry the front cover off at the specified locations, looks like deep splits in the cover. Try to keep it clean but buff the red sealant off now before you install new parts. Use the flywheel to turn the engine over so the bolts line up with the holes in the bull gear. After the bull gear is removed, remove the idler gear (top left), remove the cam gear. Clean the front end with mineral spirits and dry with compressed air. Now, turning the engine by the flywheel in direction of rotation, put the timing mark at TDC. Timing mark on new bull gear (either a straight line or "V" mark) will determine which mark to use on the crank gear. With that done, install the idler gear and cam gear. When sealing the cam gear, use new O-ring and "football" gasket. When you install cam gear, use grey gasket maker where the football gasket seals on the cam cap splits. If you don't.....it WILL leak there! Now, leave the idler gear loose enough to where you can move it by hand but snug. "Eye" the timing marks on them and get them close. You cam now hold the bull gear up and align all the timing marks. ALL marks MUST line up at this point. You can tighten the bull gear to specs now (I think its 50ftlbs but not 100%). Now you need to set your back lashes. On used gears I think its .006-.012 allowance. Once backlash is achieved, tighten the idler nuts to 80 ftlbs. Your done with gears! Now, buff the front cover mating surface and apply red antirobic cream to the mating surfaces and spread it out evenly. Place the front cover on and remember, the sealer cures with the lack of air so you have limited time to get the bolts in and torqued. Front cover bolts torque to 50ftlbs. You WILL need a seal installer, yes you can tap it in but take a good chance of the seal leaking. Install the seal and front engine mount. Make sure to use grey gasket maker on the splits of the front and rear structure when installing the oil pan as well. Install the rest of your front cover components and radiator! ALL DONE!!!:biggrin_2556:
     
    truck567168, tnpete, BabyGator and 4 others Thank this.
  7. catmechanic07

    catmechanic07 Bobtail Member

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    FYI.....a bull gear failure doesn't mean automatic overhaul. Usually the larger gear gets teeth broke off first and it eats that, crank, and acc drive teeth.

    Bullet proof? NO! Detroit says replace around 5-800k miles, at overhaul, or if front cover is removed.

    Replace bearings.....not an idea that just ANYONE should attempt. REMEMBER.......your driving a truck for a reason and may be good at it. LOL.....you know where this is going.....You cant be good at everything. Stick to driving the rigs and leave the mechanical work to us mechanics. We'll leave the driving to the drivers!! Mechanics and drivers are a breed of their own.
     
  8. truckman29801

    truckman29801 Medium Load Member

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    ^^^^^^^^^^ this guy just changed the bullgear for the 12.7 engine that sits in the depths of my brain haha. Usually the truck that sits in the backyard of a Truck drivers yard is a failed mechanical experiment . Seen it too many times, guys with trucks missing heads, transmissions, rear chunks missing, easy to disassemble but sometimes they cant put it together again.
     
  9. catmechanic07

    catmechanic07 Bobtail Member

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    ^^^^^^^^^^^ Is that a compliment or a bust? I work on junk daily. We have parts trucks sitting around with no heads, no rears, transmissions gone and I put them back together. I actually build trucks, engines (all makes and models), rears and build every one from JUNK. Saving a dollar one dime at a time!!!


    Questions: PM me and Ill try my best to help out. I have 13 yrs diesel exp and don't see an end in sight!
     
  10. GrapeApe

    GrapeApe Road Train Member

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    Whether or not it should be replaced depends on the type of gear train you have and if it's worn. If you have the compact gear train, then the bull gear is pretty much bullet proof, check lash and condition of gear teeth and keep running. If not, then I'd change the bull gear. The compact gear train uses a bull gear with a bushing mounted on a spindle, which is much tougher than the roller bearing style. I have yet to see a bull gear failure with the compact gear train. I'm sure it can happen, too much play can destroy other parts just the same, but you don't have to worry about a sudden failure like you do with a roller bearing.
     
    starmac Thanks this.
  11. truckman29801

    truckman29801 Medium Load Member

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    oh it was a compliment all the way brother. Ill def pm you if i cant handle something, I know what you mean about people and their junk, but if i do that i get a feeling of giving equipment a new life, or a sense of accomplishment knowing you did something.
     
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