Diagnosing Drivetrain Noise (now with pictures! well, at least one picture...)

[bigred88]

A couple weeks ago I started getting some noise somewhere in the drivetrain, and I'm trying to narrow things down before I start pulling stuff apart, and I was hoping someone would have a pointer or two.

88 K5, 350/700R4/10 bolts/31" tires/193,000 miles/don't know off the top of my head if it's a 208 or 241, I'll have to check. The whine sounds like gears contacting-high pitched, kind of along the lines of a gear drive timing system or a blower (not exactly, but that's the closest I can describe it). From in the cab it sounds like it's coming from the rear diff, but sound can travel weird sometimes. At first the noise was only at higher speeds, 60 and up, and it would stop immediately if I took my foot off the gas, and start right back up when I touched the gas again. This week I'm getting the noise as low as 30-35, so whatever it is, it's getting worse. There's also a bit of a grinding/clunk on the 2-1 shift, but that may have been there for a while and I just didn't notice until I really started listening because of the other noise.

Checked diff oil level and tranny fluid level- both good (edit: t-case was a pint low- I have a very slow leak, topped it off, no change in the noise). The tranny fluid is 2 years/20k miles old, diff oil 5 years/45k miles old, both are Mobil 1. Nothing wrong with the appearance of the fluids, either.

And that's where I'm at. I figure my next step is to pop the diff cover off and inspect the gears, but I'm not sure what I'm looking for other than obvious damage.

Anyone have any insight, or other tests to run to help pinpoint the problem? Thanks!

 

[496truck]

Are you familiar with checking backlash or using gear marking compound to check your gear wear pattern?

I see some diff work in your future. It could be as simple as worn pinion bearings causing pinion to ring gear deflection and noise. Or it could mean an axle rebuild with new gears.

 

[bigred88]

I have approximately zero experience with differentials. Always glad to learn something new though- the only reason I don't have any experience is that I haven't had any trouble before.

 

[496truck]

Now is a good time to learn. Start by doing some research on it.

One easy thing to check, chock the front wheels, jack and support the rear axle. Now put trans in N. Slide under and grab the pinion. Try rocking it up/down/side/side/in/out. Any movement is unacceptable. Rotate it by hand, see if it feels abnormal and listen for noises. This is also a good time to check the u-joints for wear. I like to remove the shaft completely so that I can rotate the caps in my hand to feel for anything funny. Worn u-joints can cause all kinds of noises at speed, but the whine you described sounds like gears.

 

[bigred88]

Thanks for the replies! I'll start doing a little reading, and check the pinion.

The u-joints were replaced the same time I changed the tranny fluid, so they should still be fine, but stranger things have happened.

 

[bigred88]

So I finally got the diff open, and here's what I've got so far. The oil has a lot of silver metallic streaks in it. Also, when rotating the tires so that I could get a look at all the gears, I noticed that for about half of the travel it is very difficult for me to turn the wheel, then the other half one fling and it will continue to rotate through that half of it's travel. It is dependent on the actual positioning, meaning I'm seeing the same part of the carrier every time it's loose, and the same part every time it's tight. Is that normal? Doesn't seem to me like it would be. Sorry if that's a dumb question, but this is pretty much my first time opening up a diff, so I'm quite the noob at this point.

Next question comes with a picture:

The part of the carrier that I boxed in red seems to me to be acting funny. As the wheel rotates, this piece goes back and forth between moving and not moving, and when it is moving it's making a clunking noise. Again- I don't know if that's normal, but it seemed strange to me.

I did try moving the pinion around, no movement there, but there seemed to be a lot of rotational slop. I haven't checked the backlash yet (heading back out to do that now), and haven't checked the wear pattern yet, either.

Thanks for any answers, tips, etc.!

 

[bigred88]

Ok, I checked the backlash. Actually, I checked it when the carrier was on the side when it spins freely and again on the side where it's really tight. I got two different readings- .008 on the tight side, and .030 on the loose. Am I doing something wrong here, or is my diff just effed up? It is my first time checking backlash, so I'll admit the possibility I'm doing it wrong, but it seems pretty straight forward.

 

[bigred88]

Alright, last update, I'm done for the evening- too cold out and my fingers are numb.

I spent a little more time messing with the backlash and trying to get an accurate reading, and as near as I could tell it's around .008, but the whole carrier and ring gear kept deflecting downward. I would get to around .008 on the gauge, and there would be a bit of a stop, but I could keep pushing right on to .050 or more without the pinion rotating- all the extra movement was from the ring gear moving up and down. Plus, if I attempted to rotate the pinion as if the truck was in reverse, the carrier/ring gear would very noticeably pitch downward before any wheel movement began.

It seems to me like I need to go ahead and tear the whole thing down, my instincts say there's a messed up bearing in there somewhere- anyone else have an idea as to what exactly is wrong?

 

[K85 Octane]

what the hell is that? LOL

is that the Gov lock?

 

[bigred88]

Yep.

 

[rebelgregory]

Yes. That's the Gov-Lok. I've 'energetically disassembled' a couple of those before converting to tons. You should be OK with 31" tires though.

On to your findings. .008" of backlash sounds OK. .050" of carrier deflection is not. If you're positive that the pinion is not moving and you're still getting that much carrier movement, your diff is done. You're carrier bearings are gone. Running it longer will only require more work, or a new axle.

Just looking at pic, your gears look OK. You could pull it and just replace bearings. By just replacing the carrier bearings, through some fine measuring, you can be pretty confident of what shims (if any) you'd need to move around.

If it were me, any more work than this would warrant picking up a clean 10 bolt from somewhere. Most people here would agree that it's not worth sinking a ton of time and money into a 10 bolt, but your specs don't equate to a hardcore wheeler, so I'll spare you the 1-ton recommendation.

 

[blazerz]

x2 on the carrier bearings......check the carrier for crack's...i have two of them, both cracked in the same place....they acted the same way, tight for a little rotation then free....one axle is still in one i am driving..... gov-bomb......

 

[bigred88]

Thanks. I went ahead and started gathering the stuff needed to replace bearings today. Since all of the gears looked good but I had a lot of metal in the fluid, I figured one of the bearings had to be on it's way out.

I'll look over the carrier really close for cracks when I get it out next weekend. It looked good from what I could see, but I'll make sure to double check.

Yeah, I've got no real plans to go any bigger on the tires, maybe 33s someday, but most of what I do is just daily driving. I like getting off road, but those days seem to be a lot more rare than I'd like. And I thought about just looking for a whole other axle, but I figure that's just a crapshoot anyways, if I go through this one then I'll know I've got a good one under there for the next 100,000 miles or more.

Thanks for the feedback! I'm sure I'll be posting more questions this weekend as I dig into it.