Strange noise that I cannot figure out... (1 Viewer)

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Oct 20, 2008
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6 months ago I had the pinion nut back off on my while I was driving, so I replaced the third member. While I had everything apart I redid the rear brakes, had the drums resurfaced, new pads, adjusted everything as per FSM. Now I have some strange whining noise that I cannot locate.

- The noise is barely audible in 2nd gear, gets louder in 3rd, and loudest in 4th.
- The noise is only audible when I am trying to accelerate (Goes away when I let off the gas or when I put it into neutral)
- The noise only comes out in high range (2WD and 4WD), goes away in low range
- The noise does not show up when the t-case is in neutral and I go through the gears
- the noise gets louder up to 2500 RPMs, and then drops off substantially
- It is not coming from the engine bay, definitely tranny/t-case or back
- The noise is there with the front hubs engaged and disengaged

Last night I dropped the rear driveshaft and examined the pinion flange, and I did not have much play at all. I could turn it maybe 4* either way before it stopped (Parking brake was on).

I got new tires yesterday (Went from 33" to 31"). I was hoping this would help, but it has not

My working theories: U-joints could be bad, Pinion bearing in the new third may be bad (Could just swap front and rear maybe?), warped brake drums? (O'reilly royally screwed them up when they did them, took three tries to get it to where I couldn't feel scoring)

Any thoughts? Ways to narrow down the problem?
 
To summarize, it sounds like the noise changes with speed and load. It does not follow the trans gear per your shifting in neutral test and does not follow engine RPM. It's not a vibration or pulse so does not fit the bad ujoint or warped rotor types of sounds/vibrations one would expect. Low range means slow wheel speeds so again it is following vehicle speed. Bad wheel bearings often tend to growl.

I believe you have a ring and pinion issue. Whining is very typical sound from ring/pinion alignment and/or wear issues. The whining will get louder with speed and will change tone or go away depending on load (accel, decel, or coast). Even if you have the backlash correct, incorrect pinion depth will eat up the gears quickly. If I am right, you may very well need to replace the ring and pinion already. I would pull the third and use the marking compound to ensure you have proper depth and tooth-centric gear contact (search, many many pictures/examples). If you have never rebuilt a third member, now might be a great time to learn. You will want to purchase some tools like a magnetic base/micrometer set up for lash, make or buy something to adjust the side adjusters, a press for bearings, and of course torque wrenches. You can purchase rebuild kits with new bearings etc... If you want to go in there once and be done with it, I'd get new gears and a rebuild kit. If you want to keep costs down pull it, inspect the gears, if the pattern cannot be corrected through backlash adjustments, purchase a crush sleeve and pinion shims to get the pattern right (still need all the tools...). If you still cannot get the pattern right then you will need to purchase a new ring and pinion gear and probably new crush sleeve.

But it all starts with getting the third member out and assessing the gear mating pattern.

Frank
 
If the noise is engine rpm dependent as you mentioned (drops off above 2500 rpm), then the noise is either coming from the engine or transmission. Not the transfer, not the differential, not the rear axle components.
 
if it's your dd and you can't open it up yet, maybe remove the DS and drive with the front axle to reduce wear on your rear 3rd
 
Torque is dropping off over 2500 RPM which can easily reduce the volume level but that it is heard louder and louder as speed increases in each gear suggests while impacted by what the engine is doing is not following the engine specifically.

If you have something whining from the engine like a belt or something you should be able to hear that sitting still revving it up and down.

Frank
 
Thanks for the input guys! I really hope it isn't the R&P! I will drain the fluid this weekend and check to see if I am seeing metal flakes that should tell me if the gears are eating each other up.

Small update: today after I drove for a while I splashed water on the brake drums just to rule them out. Surprise! The Drivers side steamed immediately, while the Passenger side did not. Regardless, I need to tear into that and get that drum machined (again). I will do that and hopefully that will make it go away, or at least remove some noise and let me be more precise with what I am looking for. Maybe it's just "dropping off" because the engine noise is louder and drowning it out? I listened really carefully today as I drove and it did not drop away completely as I said earlier, more gets muted.

Searching through MUD, I found a test for the pinion bearing: bump it while in gear and watch to see if the flange moves up and down. Ill do that tonight and post results.

I will try to get to this over the weekend and get back to yall asap with an update.
 
Sounds like you are on the right track. A lot of noise gets louder with speed on our trucks, wind, every moving part, etc... so it is understandable that the whining could be less pronounced. Right now my truck's body is sitting on the frame due to flattened out body mounts and it is very loud making nasty noises when the frame flexes at all rubbing on body seams. The 2F's torque curve plummets after 2500 RPM and thus that might also reduce the volume of the whining.

Keep in mind that the diff could pass that test and still have an R&P issue. Nevertheless, more data points can never hurt.

Frank
 
does it pull towards one side while you're driving like the brake is dragging?
 

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