1986 C10 drivetrain noise - can't locate

[mcintyrederek]

1986 C10 LWB with 350, TH400, two piece driveshaft, 10 bolt 2.73 rear.  Running 15" 1988 C1500 rims with 31" tires..

The TH400 has a tail extension piece on it. 

So far I have replaced all three U-joints, center carrier bearing, and both rear axle wheel bearings and seals.  The front wheel bearings look good and turn freely with calipers removed, with no noise, by hand.  They are tight and the grease looks good. 

I am getting chassis noise while driving, especially above 40 MPH.  At 55 to 60, it sounds like a bearing somewhere, but as you see, I've replaced the main suspects.  It is a continuous "roar" sound (like a bad bearing sounds) and keeps consistency related to travel speed.  Are there other bearings I need to look at?  Is there a bearing on the tail extension unit out of the transmission that may need attention?  The rear end looks good and the pinion and carrier bearings feel tight, the oil is good.  Even though the front wheel bearings look and sound good when turning by hand, how much of a suspect can they be?  It really sounds like it's coming from the back, until I shut the back glass..  then it sounds like it's roaring all over.

Any thoughts on where I should check next?  Thanks.

[VileZambonie]

Are you sure it's not your tires? Easy way to tell is tire to road noise changes over different road surfaces. A bad bearing will not. If you suspect wheel bearing, you can load and unload the bearing by carefully weaving the vehicle from left to right which will load and unload the bearing.

[mcintyrederek]

It *may* be the tires.  I'm starting to suspect that now.  I had cheap tubes on the exhaust..  replaced stock 235/75/R15 tires with 31" A/T tires, THEN put Walker Quiet mufflers on it.  It was at that time I noticed the noise..  I didn't notice the noise when the loud tubes were on the exhaust..  Maybe I don't have a bad bearing after all.  Still..  Is there a bearing on the output of the transmission tail shaft extension that I need to check?

[VileZambonie]

It's a bushing

[mcintyrederek]

Alright, thanks.  Well, that pretty much eliminates all my bearings.  I'm leaning towards the tires now.  They are cheap Chinese "Good Ride" brand (all I could afford) A/T 31" on 15 inch rims.  I went from Michelin 235/75 series to these.  Maybe this is my whole problem, "Good Rides" might not be the best ride for noise..

[LTZ C20]

That is not a brand I have heard of before. As Vile stated, try the weave method. Also, when it's making noise, let off the throttle then apply again, do that a few times. If the noise changes or stops, you may need to recheck your rear diff. That method applies and releases load on the rear end. If it's making noise it will generally stop or get quiter when you let off the gas. You can also slip it in neutral, that will make noises change also if the noise is in the power train. My first suspect would be tires tho.

[mcintyrederek]

The noise is consistent with road speed, not just during acceleration.  I can be cruising at 55 and drop it in neutral and the noise is still there.  When I changed the wheel bearings, the rear end gears LOOKED good, and so did the oil..  but I don't know how many miles is truly on the vehicle, and how "worn" the gears may be.  The odometer 1st digit has turned over probably several times. 

"Goodride" tires are made in China and are relatively cheap.  I just checked my air pressure and was reading 38, which seemed high for that size of tires.  I dropped it down to 30 and going to do a road test tomorrow and see if the noise changes at all.

Thanks for the replies.

[LTZ C20]

It's still possible for a rear end to make noise even while at a constant speed, just so you know. I would look into a cheap set of "name brand" tires. Rear end gears can still look ok but be worn also. Tire pressure doesn't usually make a noise unless it's drastically under or over pressured. 8 pounds won't really do much. Usually irregular wear, odd ball or aggressive tread patterns and oddities in the rubber will cause noise, such as patches of varying densities of rubber, internal or external flat spots, internal or external welts, just to name a few.

At this point I think we are getting back to tires as our main suspect. Check the date code of the tire, you can get new tires that have been sitting on a shelf for 4 years, they can go bad even tho never used, especially if it is a low grade product.

[mcintyrederek]

I don't guess it would really hurt anything to jack the rear end up, remove the wheels and drums, crank the engine and put it in drive at idle speed..  crawl under and listen to see if I hear anything suspicious?  I know that without a load on the drivetrain that major noise won't show up, but I don't see what it could hurt to try.  I have a stethoscope I can use, but I don't really know what is "normal" noise and what's not.

[LTZ C20]

Yea you could do that. Just be extra careful, chalk the front wheels, put the rear on jack stands, lay on a creeper so you can roll out quickly if necessary.

Just so you can get an idea of what it's supposed to sound like, start your engine, then put your stethoscope to the body of each of the accessories on the front of the engine, i.e. water pump, alternator, p/s pump etc. It should sound rotational but smooth and quiet. Like a washing machine on spin cycle, with your stethoscope your gonna hear it but it should be smooth, like a washing machine as I said. If it sounds like a belt squeeling or a kitchen blender trying to blend ice, very loud and grindie and like something is going explode then there's a problem.

[Irish_Alley]

i wouldnt craw under it unless you had some help. see if you have any friends that have the same bolt pattern and try to swap them wheels

[mcintyrederek]

Alrighty..  I can get some help first of the week and listen with stethoscope.  Also I have a buddy with 5 on 5 rims with Goodyear tires and his ride is quiet, may change and just see if it makes a difference.

Thanks for replies.

[LTZ C20]

That's the best place to start.

[Stewart G Griffin]

1) i was going to suggest the tires too.  Being that you have a cheap Chinese brand, it would not surprise me......

2) i would definitely not get under the truck or have it run in gear unless someone was in the seat.   And if you take both wheels/drums off then won't the axles turn in opposite directions thereby throwing the test off because now the spider gears are going to go at full tilt?

[mcintyrederek]

I guess that's why I need some control over each wheel on the back.  Keeping the drums and wheels on would give me the ability to lightly brake, simulating a "load"..  of course, like you said, I'd need someone in the cab to do this while I'm under the truck to begin with.  I'm going to go with the cheap tire theory.  I wish I had changed to quiet mufflers BEFORE changing tires.  Then, it would be obvious if the tires indeed are making the noise.