Drive train whine (1 Viewer)

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My cruiser has developed a driveline whine while "ON" the gas. 96 cruiser with lockers. Stock gears. diffs never opened.

-I have taken off the rear DS and it is still there. with cdl locked.
-New knuckle rebuild. Noise started before knuckle rebuild. been getting louder with time.----
-Output flange on tcase feels very tight with no slop in any direction.
-Front pinion doesn't have any slop either.
-whine/humm starts at EXACTLY 20mph everytime
-Whine/humm goes away completely when off gas
-Whine/humm gets less noticable at higher speeds but is still there
-Brand new DC front shaft
-New diff fluid. Old was pretty new but just changed. No metal in fluid at all.
-Noise is the same stone cold or after driving for awhile

I am thinking pinion bearing but not sure since its tight.

Any help would be great. Thanks
 
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Den Lors sells J S steel man electronic ears, 6 in a set. They take the guess work out of drive train noises. They mount under your car , price under 200. Mike
 
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inkpot

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You tried it with the rear DS pulled, but you did not try it with the front one pulled out? That would be my next step. John
 
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I have heard of those. Seems like it would work well. Could use them in the future also. Anyone renting a set??
But I am also looking for some other tests I can do to figure out where its coming from other than what I have done so far.
Den Lors sells J S steel man electronic ears, 6 in a set. They take the guess work out of drive train noises. They mount under your car , price under 200. Mike
 
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I recently put conventional gear lube in my transfer case (use to be synthetic) and it significantly reduced the whine I was experiencing.
 
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I was thinking pulling the rear shaft tells me its in front. I can feel and hear it in the front. Also long story short the next time my DS comes off so does my tcase to intsall two new studs on the output flange. PO cross threaded two of the nuts.
You tried it with the rear DS pulled, but you did not try it with the front one pulled out? That would be my next step. John
 

inkpot

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I was thinking pulling the rear shaft tells me its in front. I can feel and hear it in the front. Also long story short the next time my DS comes off so does my tcase to intsall two new studs on the output flange. PO cross threaded two of the nuts.
Pulling the front also would then eliminate both drive shafts. Lots of other parts that move in the driveline. John
 
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Anyone else with some ideas? I really want to stay away from taking off the front shaft since the 2 studs are stripped. I would have done it already at this point.

What parts worn would cause the hum in the front that starts EXACTLY at 20mph and up. Quites down around 50. There is no vibration going on at all.

Full list of what I did so far is on my first post. THANKS
 

landtank

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off gas whine with two different drive shafts would point me towards the front diff possibly needing a rebuild. How many miles and have you checked the drain plug for shavings?
 
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It has 206k miles. The whine is "ON" gas only. Also goes away in nuetral. I just changed the diff lube and it was still looking really good with no shavings. I took off diff side of driveshaft and there seems to be no play on the diff output.

Is there anyway to check the pinion bearing without a complete removal of the third?

Technically I didnt change out the front shaft because of muckered up studs on tcase side. But I highly doubt its that since I just bought the new DC shaft. Seems like the noise just kind of crept up over time.

off gas whine with two different drive shafts would point me towards the front diff possibly needing a rebuild. How many miles and have you checked the drain plug for shavings?
 

Hoosier Daddy

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Three thoughts -

You've ensured the pinion/shaft angle is near zero degrees?

Chassis ears are available on ebay for $125 or less. They won't help much if your driveshaft is the source but can help narrow it down if the whine is coming from the diff.

Tap and die set to clean up the tcase studs?
 
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I didn't check the pinion angle but the diff. is pointing at the tcase output and I have a DC. and lantank castor plates.

Chassis ears would be cool.

Dont think the die will work as there are no threads on the first half of the stud. Just good threads on the other half. I took out the lock washers for those two studs to gain more bite. Also used red loctite in replacement of lockwashers. Ghetto for now until I take out Tcase.

Also one question..... If I was to take out the front shaft I am sure the noise would disapper regardless because there will be no load on the front pinion. Now it only makes noise when on the throttle. Off throttle or in nuetral there is no niose. Am I way off??
Three thoughts -

You've ensured the pinion/shaft angle is near zero degrees?

Chassis ears are available on ebay for $125 or less. They won't help much if your driveshaft is the source but can help narrow it down if the whine is coming from the diff.

Tap and die set to clean up the tcase studs?
 
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I have a possibly similar situation with my '91. On gas, there is a constantly louder whining noise coming from what is strongly the front end of the truck, which gains pitch/loudness with speed. It almost accounts for half the noise in the cabin at highway speeds, but as soon as I let off the gas, or it coasts, the whine is gone.

I am guessing I'll have to get some good time in with the pinion/diff area and figure this out one by one as well. There is plenty of slack (about 15-20 degrees?) between the front tires and center shaft turning when spinning them by hand. That's true for the rear shafts/diff too though (plenty of drive train slack).
 
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If you're really careful you can crawl under the truck with the axles up on stands and carefully accelerate with the tires in the air.

Don't touch anything that spins. Do this on concrete with sturdy stands. Listen around with a mechanics stethoscope. Put a bit of load on the driveline by gently applying the brakes.

Takes two people to do this, but you should have a really good idea of what's making the noise almost right away.

Most whining noises that go away or change on accel/decel are final gear noises. Have a good listen to the nose of the diff carrier when everything is spinning.
 
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My starts exactly at 20 mph while on gas only. Would this be dangerous to check while on stands? Maybe I can get my hands on a friends lift.

What is the usual problem with final gear? Can this be put off for awhile if it is the case? The noise doesnt bother me much.
 
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I'd actually prefer 6t jackstands to a vehicle lift. These trucks are super sketchy when balanced on a hoist.

If its the final gear, it will eventually blow up and leave you stranded unless you do some CDL stuff and pull the front propshaft and both front drive plates.

My guess is a bad pinion bearing causing gear mesh issues. Have a listen with a stethoscope to confirm. Then tear down and repair.
 

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