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Calling Differential Guru

Discussion in 'Truck & Equipment Repair' started by jb1390, Jan 28, 2014.

  1. jb1390

    jb1390 Senior Member
    Messages: 710

    My truck is making noise (sounds to me like gear noise), in 4wd at speeds in excess of 30 mph.

    The noise is not there when I'm coasting. It gets louder the harder I accelerate. It is also there when decelerating, but doesn't seem quite as loud. That could just be that I can't decelerate (under engine load only) as fast as I can accelerate.

    99% sure this is the diff and not t-case, I just had the t-case apart because I thought that was it, and it's a 2 year old unit so I wanted to make sure everything was ok while I still had a shot at warranty. All looks good inside the t-case.

    As far as the diff:

    I checked backlash from the yoke (9.25 ifs) - and I got .030, which should correspond to either .015 or .021 backlash. (either divide by 2 or multiply by .7, different manuals alternate between the two methods)

    I checked rotating torque on the pinion-just until it hit the ring gear, so a very small amount of movement. I know running torque 'should' be lower than this. The pinion moved at around 3 in-lbs, maybe a little less.

    No noticeable shavings when I drained the oil.

  2. cubicinches

    cubicinches PlowSite.com Addict
    Messages: 1,415

    Sounds like a bad pinion bearing(s). Which, if we're talking about the truck in your signature, isn't uncommon.

    .015 - .021 backlash isn't going to create noticeable gear noise.
  3. jb1390

    jb1390 Senior Member
    Messages: 710

    We are talking about the truck in my sig-02 duramax with the 9.25" IFS diff.

    Any chance tightening preload to get back to 10+ inch pounds will do anything? Or will it just cause the degrading bearings to pop earlier.

    From my limited experience and reading-low bearing preload allows everything to flex, which can cause gear noise under load since the pattern isn't good.

    I'm wondering if there's anything i can do besides a full rebuild-and if I am hurting anything by just living with the noise for the rest of the winter.
  4. cl733

    cl733 Senior Member
    from Canada
    Messages: 263

    Is your pinion loose, when you wiggle the drive line, the lock nuts usually never back off, so if you have a lot of clearance there then maybe something has worn a lot, check your knuckle ujoints really good , a bad ujoint there can give you a lot of symptoms
  5. cubicinches

    cubicinches PlowSite.com Addict
    Messages: 1,415

    It's not likely that tightening the pinion will do anything but finish off the bearings. If the diff has a lot of miles, and has .015 -.021 backlash, then the pattern on the gears isn't any good anyway... but that's of little consequence at this point anyway, as the gear set is worn as a pair. New bearings should require about 25 in. lbs. of torque to rotate when properly preloaded. Used will be 10-15 in. lbs. If 3 in. lbs. is an accurate measurement, then you've got failed/failing bearings.
  6. jb1390

    jb1390 Senior Member
    Messages: 710

    That's kind of what I thought at this point, but wanted to verify.

    There is no play up and down that I can detect, and the u joints are good-they are only 2 years old also.

    The torque screwdriver I used is calibrated, brought it home from work. and it's a deflection style, not a cam/click type. I'm pretty sure the measurement is accurate.

    So I guess what I'm hearing is to leave the setup alone, and plan on a rebuild or buying a rebuilt unit sometime in the near future.
  7. jasonv

    jasonv PlowSite.com Addict
    from kannada
    Messages: 1,122

    Just to cover all the bases, are you certain that it isn't a wheel bearing? 4wd will change the stresses on everything. Does the sound change at all when you are steering? Or is it consistent as long as you are under the same load?
  8. jb1390

    jb1390 Senior Member
    Messages: 710

    It is not a wheel bearing, and they are new. That sound wouldn't change drastically when in 4wd vs 2wd.

    I don't steer fast at 50 mph in 4wd, so no, I do not notice a change when steering.

    The sound is pretty consistent under the same load. It is not a cv joint, it is not a u joint, I am very familiar with the symptoms of those failures.
  9. sameoldthang

    sameoldthang Member
    Messages: 34

    front diff

    Drop the drain plug in the front diff and its probably gonna look gray and chunky.

    Those differentials are pretty easy to rebuild. I have done many of them on the half ton trucks including mine 06 Avalanche. Your gonna need a bearing kit with races and locking tabs for the carrier bearings that the chevrolet dealer has in stock. I can walk you thru it if need be the only tedious part is setting the back lash with a dial indicator on the yoke. I think the backlash spec in .006-.0012 off hand but i can look it up on alldata. I set the pinion preload to a tight door knob setting as a old timer showed me. I have rebuild a lot of front and rear axles on these trucks its not too bad.

  10. jb1390

    jb1390 Senior Member
    Messages: 710

    So I did drain the oil, and it looked like normal, used gear oil. No chunks, no filings, a little bit of very, very fine metal dust on the drain plug, but that is pretty normal from what I have seen.

    I need to get the truck put back together and bring it over to a friend with a lift, and try to replicate the noise to verify where it's coming from. I'm pretty sure it's the front diff-my hunch is that the front pinion bearing is shot, and allowing play, causing poor gear contact pattern which is what's causing the noise.
  11. sameoldthang

    sameoldthang Member
    Messages: 34

    jb1390 letting your foot on and off the gas and the noise is audible with acceleration and the axle is live its a pinion bearing. On a carrier bearing you can turn the vehicle left and right to load and unload the bearing to diagnosis. Pinion bearings are cake if you have a press I can walk you thru if need be. Its so not fun to R&R the front axle so have some help and a lift.