Low pitched humming at high speed front end (1 Viewer)

bajaphile

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Hi all, sorry for yet again another noise thread, but need some ideas.

Problem:
- Starting exactly at 75 mph a low hum which sounds like similar to a worn mud terrain starts coming from the front end. The noise is pretty quite, but it is felt slightly throughout the truck.
- It is consistent and gets slightly worse as you go faster (85 is about as fast I can go).
- Started after a long offroad trip last month. Noise does not seem to be getting worse with time.
- Shifting to neutral and coasting does not impact noise at all
- Accelerating or coasting does not impact noise
- Removal of front DC drive shaft fixed noise, but rebuilding it and re-installing it did not help. The noise is being caused by the front axle getting power.

What I've done, not any of this has changed the noise at all.
- Rotated tires
- Replaced front diff fluid
- Rebuilt front DC drive shaft with new U-joints and re-balanced at Drive Shaft specialty shop
- Topped of knuckles with grease
- Repacked front wheel bearings and checked preload. PS spindle does show a little bit of wear on bearing surface...
- Checked knuckle nuts

My thoughts on what it could be, but not sure if there are ways to easily check:
- Front spindle. I rebuilt the knuckles probably 10k ago and the space between the spindle and axle appear to be fully greased. The surface for where the outer bearing may be starting to wear, but hard to tell. Might just need to pull spindle off and check.
- Pinion bearing. 4.88 gears done by Zuk about 15k ago.
- Xfer case output bearing

Any input or things I can do to check components that are potential suspects? Thanks for your time.
 
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Sorry it's early in the morning here, and i haven't had my coffee yet so i missed that part of you're post.
 
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Just another though, i konw you said you have a DC drive shaft, but have you tried unbolting it and changing the phase by turning it 90, or 180 degrees to see it the hum goes away, or changes at all.
 

bajaphile

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Well, I've had the DC front shaft for 8 years and it was always in phase and never had a vibration ever. When this popped up after a long wheeling trip, I thought it was just the u-joints that needed to be replaced. Felt like a drive shaft related thing, so when I pulled it and took it on the freeway and the hum went away, I thought that was it.

Drive shaft shop replaced the 3 u joints, checked CV and splines and rebalanced it. If I were to put it out of phase, it would throw the balance off.

It is definitely related... some component when getting power from the drive train is causing it. I don't think there are really that many options. Either differential bearing(s?), wheel bearings or brass bushing. All of which have certain noises and none seem to be consistent to what I'm getting. I am really surprised that repacking the wheel bearings did not offer any change.
 

baldilocks

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Are the front arm bushings good? Is it possible that deteriorated or damaged bushings could have allowed the pinion location to change thereby causing a driveline vibe?

The fact that the noise goes away when the shaft is removed and it does not change whether coasting or applying throttle tells me that it’s not in the axle because driving minus the shaft is the same to the axle assembly as coasting with the shaft installed.

Add in the fact that you went through the knuckles and wheel bearings recently and Zuk rebuilt your diffs only 15k miles ago.
Or, maybe it’s coming from the forward transfer case output bearing but you just think it’s the front end. Have you verified oil level in the transfer case? Happy Thanksgiving .....
 

bajaphile

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A dry spindle bushing will howl. Pinion bearings? How much deflection does the pinion shaft have?

Hi Cruiserdan,

Pinion rotates back and forth at the differential by about 0.125" (rotational play), which I believe is acceptable. Other than that, the pinion flange at axle end does not have any other motion or play. Same can be said of the flange off the transfer case. The rotational play at that flange may have been a little bit greater there. I was not measuring, only estimating.

Are the front arm bushings good? Is it possible that deteriorated or damaged bushings could have allowed the pinion location to change thereby causing a driveline vibe?

The fact that the noise goes away when the shaft is removed and it does not change whether coasting or applying throttle tells me that it’s not in the axle because driving minus the shaft is the same to the axle assembly as coasting with the shaft installed.

Add in the fact that you went through the knuckles and wheel bearings recently and Zuk rebuilt your diffs only 15k miles ago.
Or, maybe it’s coming from the forward transfer case output bearing but you just think it’s the front end. Have you verified oil level in the transfer case? Happy Thanksgiving .....

1) I'll need to really try hard to get a visual of the bushings on the truck. Not sure if there is an easy way of checking. 200k miles on it and most likely getting to that time.
2) Haven't checked transfer case fluid. I swapped it out when I got the truck 8 years / 60k ago. It might be due for a change...

Another thing to note is that I have had to change my front diff fluid every 6 months or so because it gets so jammed up with Moly from the knuckles. I must have pushed moly into the axle housing during my last rebuild. I've read it isn't the end of the world but may cause more foaming. Just thinking out loud here, but hopefully it didn't cause the pinion bearings to wear prematurely or something.

Last thing is that I drove it with my buddy in the car as passenger and we think the rotational noise is at the frequency you'd expect at the wheels (wheel bearings, or wheels) and not 4x the rotational speed of the driveshaft. But even together we are still idiots and I'm still not convinced.... ;)
 

bajaphile

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Bumping this unfortunately. Any more ideas on what and how to check components?

I keep going back and forth and now I'm leaning towards front DC drive shaft again. The guys rebuilt and balanced it, but who knows... maybe the splines are worn, or the CV ball is worn? I greased both and no difference. Sure sounds like the DC shaft is the one vibrating, or possibly I do indeed have a bad wheel bearing? I would imagine repacking the wheel bearings would at least offer up a temporary fix? WB's have roughly 15k on them.

I got underneath and grabbed the front shaft and really tugged on it as much as I could. No deflection or anything. Just the assumed rotational play which I feel is within spec.
 

baldilocks

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Bumping this unfortunately. Any more ideas on what and how to check components?

I keep going back and forth and now I'm leaning towards front DC drive shaft again. The guys rebuilt and balanced it, but who knows... maybe the splines are worn, or the CV ball is worn? I greased both and no difference. Sure sounds like the DC shaft is the one vibrating, or possibly I do indeed have a bad wheel bearing? I would imagine repacking the wheel bearings would at least offer up a temporary fix? WB's have roughly 15k on them.

I got underneath and grabbed the front shaft and really tugged on it as much as I could. No deflection or anything. Just the assumed rotational play which I feel is within spec.
Warn bushings affecting pinion angle under load?????????
 

bajaphile

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Well the vibration is being felt/heard independent on load. Just vehicle speed. Accelerating, decelerating, coasting, etc... no change.

After driving today, I'm definitely feeling it is drive shaft related. Just frustrating to get it inspected and rebuilt and still having problems after 5 years of not ever having an issue.

It feels like what the front end felt like with the stock drive shaft after lifting prior to a DC shaft installed.
 
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Well the vibration is being felt/heard independent on load. Just vehicle speed. Accelerating, decelerating, coasting, etc... no change.

After driving today, I'm definitely feeling it is drive shaft related. Just frustrating to get it inspected and rebuilt and still having problems after 5 years of not ever having an issue.

It feels like what the front end felt like with the stock drive shaft after lifting prior to a DC shaft installed.

If the noise goes away with the front DS removed and you suspect the DC shaft is the cause, then don;t run it. I've seen two exploded DC shafts that ate the transmission on the highway........
 

baldilocks

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The next logical step would be having the DC joint rebuilt, if it hasn't already been. Beyond that, a part time kit will solve all present and future front end vibrations. :smokin:
 
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bajaphile, If you happen to be lucky enough to know some of the members of your local 80 series land cruiser club. You might ask one of them if they would be willing to let you test their front drive shaft in your truck. By testing their drive shaft, you'd be able to eliminate your drive shaft as a possible source of your humming sound.
 

bajaphile

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Thanks for the replies!

This game of whack-a-mole is starting to get old...!! Spent 2 years trying to diagnose a REAR drive shaft issue. Finally fixed that and within a month I start getting what feels like a front drive shaft issue. Grrrrr....
 

bajaphile

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The saga continues...

Front drive shaft fully rebuilt with new CV ball/seat/flange and all u-joints... rebalanced..

Installed and I got up to 80 mph and thought it was fixed. Within 1 minute the humming/drone noise came back.
 

bajaphile

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I think that is a good idea for someone new to their newly modified rig... I've had the same setup for quite a while now and am used to all the "normal" noises I guess. This one is definitely mechanical and my wife can even feel/hear it (which is not a usual occurrence when I'm tracking down most minor squeaks or clunks...!)

Just went under and tugged on the front shaft. There is a slight movement when I give a good tug down towards me (as I'm laying on my back). Very slight but at whatever RPM it is spinning at going 80mph it might be the cause. Will pull it for the 3rd time, check again to make sure the output flange on t-case isn't loose and I might try getting another front drive shaft.
 
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Tachycardic

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So you don't hear the noise at lower speeds? Do you have to drive at 75-85mph? These beasts don't like to be thrashed like that, and it's letting you know. Take it easy on the old lady :p
 

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