Can a whiny driveline be dangerous? (1 Viewer)

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Sep 28, 2014
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Im getting a loud whine/whirring sound at around 65mph in my 91 fj80 from the front of the truck, only with my foot on the gas. This seems to be a common problem from what i have read. My front drive shaft squeaks at low speed as well, but Im not sure if the two are related. I changed the fluids in the xfer case and front diff but the whine is still there. From my hours of searching, I am thinking it is the front pinion bearing, drive shaft, or drive flanges (any other suggestions would be helpful). I have to drive about an hour out of town today, but I am worried that something might blow up at speed. Is this a logical concern?
 

acs

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Dec 16, 2014
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Ann Arbor MI
It's always difficult to diagnose these kinds of noises......

I too had some whine at higher revolutions, but it turned out to be the idler pulleys for the A/C and the alternator. R&R'd them out and there was no more noise. Since yours make the noise only with your foot on the gas, it could be either driveline load or something belt related...

Either way, good luck!

-acs
 
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Huh, you think? The belts are looking pretty crusty, I just haven't got around to changing them. Why would they whine only under load though?
 

acs

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Pull the idler pulley off. You don't need to remove the belts to do it, and it would eliminate one varoable...
 
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My 91 has been making the same type of noise for going on 4 years. It's never gotten louder, and there is nothing in the oil during fluid changes. In my opinion, you have nothing to worry about. I would advise you to carry tools just in case something happens. To get you rolling again if something gives out, all you have to do is pull the front drive shaft and drive flanges.
 
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Thanks dudes. Going to do some diagnostics this weekend and I'll report back. This really is loud though. Loud enough that the radio doesn't make it go away.
 

inkpot

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Any chance you put way too much grease in the slip joint? That acts like a hydraulic ram between the transfer case and the differential. Can literally put tons of force on the bearings and ujoints. Can test by removing grease zerk from slip joint.
 
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Hmmm, yes that is possible. I read that I could get rid of the "thunk" by squeezing grease in there until it oozes out of the slip yoke seal which I did. I'll pull the zirk this afternoon.
 
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I unscrewed the zirks and the rear spat out a blob of grease but the front didn't. Drove an hour out of town and back and the whine was still there. I also noticed a smell when I got out, like something was too hot. Recently I discovered that my left birf is in need of a rebuild. Could that cause a whine?
 
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If your Birf is in need of rebuild or it is very dry, it COULD be the Birf shaft in the spindle. Either a dry bushing or if it has been upgraded to the needle bearing type, dry bearing.

When you accelerate, it will torque on the shaft and put pressure on the point where it enters the spindle.

I would more likely think a pinion bearing since you have changed the diff oil (assuming oil level is correct).

Although, you mention your DS squeaks at low speed. If you have a bad U-Joint, it will also give you that type of noise under acceleration. Did you grease the U-Joints while you were there also? Once they start squeaking, it is not long before they are junk because that indicates damage. Damage = shrapnel in the cap. Shrapnel chews up other stuff. This will make them start to get loose. When loose they get out of centerline during accel / decel and can cause vibration / whirring.

Something I learned long ago when greasing U-Joints: Don't over-grease them. So many people pump in grease until the grease spews out the seals. All that does is wreck the seals and then that allows more debris in. If you do regular service, only put in one or two pumps. Don't pump it until it goobers out.

Go through and do a methodical maintenance check:
1) Check the U-joints Front and rear on BOTH DS. (If they have not been lubed in 10K miles, put in 2 pumps)
2) Check the slip joint of DS (You already did this)
3) Check grease levels in Birfs.
4) Check oil levels in Diff.
5) Check to make sure the Diff Vent Hose is not plugged.
6) Check Wheel bearing adjustment
7) Check T-Case oil type and level (You already did this)
8) If it is a pinion bearing, when you try to rotate the DS by hand with the driveline unloaded (not wheels off the ground, just no pressure on the driveline - use blocks and chocks) the pinion may move in and out of the diff when you try to rotate the DS by hand. If it does, it is the pinion bearing going out. A quick visual is also that the pinion seal is leaking.

Try those! Good Luck!

BTW: Filling the knuckles with grease will NOT push grease into the spindles because the knuckles don't get hot enough to liquefy it and let it run down to the spindles. The rotation of the axle spins it to the outside. The only way to lube the spindle is to do it when it's off.
 

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