SUPER loud hum at all speeds but 55mph

[E.T.]

Just got back from a 1500 mile drive- have noticed an issue I had before become markedly worse. It's humming sound- not a wheel bearing (too low pitched), definitely in the drivetrain as when I let the power off it stops (so is excited by torque through the drivetrain). It was peaking at 33 (barely) ,66 and 99 mph (by the clock- Idaho lets us drive at 95 when overtaking on the freeway down near Boise!), and letting off in between- now it's more or less continuous except below ~25 and at 55 (58 clock)- sufficiently bad at 70-80 that the left wing mirror vibrates! If it were a different vehicle I'd think it was a centre bearing- could it be a bearing on the transfer case? Buggered U-joint? Anyone else had this?

Cheers!

 

[Mbrooks420]

Do you have a cv joint on the driveshaft?

 

[E.T.]

Do you have a cv joint on the driveshaft?

I do on the ones going to the wheels

 

[Mbrooks420]

Usually half shafts with a bad cv are very noticeable when loading and unloading the wheel in a corner. Some second gens had CV front driveshafts, I didn’t know if the third gens were similar.

 

[E.T.]

Usually half shafts with a bad cv are very noticeable when loading and unloading the wheel in a corner. Some second gens had CV front driveshafts, I didn’t know if the third gens were similar.

It doesn't seem to matter if I'm cornering.

 

[TechGuru]

Rear differential?

 

[E.T.]

Rear differential?

maybe.. Recorded the hum, is 53Hz- divide by the diff ratio (3.55) and I get 14.9 Hz, which is the wheel frequency at the speed I was going- so presumably it's either the diff or the transfer case. Also have a spike at 159 Hz, which is 3x the driveshaft speed- dunno what significance that has.

Apologies for all the edits, math brain not working!

 

[E.T.]

I think I figured out what it is- front driveshaft. If I take it off I obviously lose 4WD- is this likely to cause issues if the system tries to engage for some reason (I don't think it ever has when set to "auto")?

 

[TechGuru]

Could just leave 4x4 high on with the front driveshaft removed...

 

[Mbrooks420]

The front driveshaft hub will just spin. Shouldn’t be an issue. What made you decide on the front shaft?

 

[E.T.]

Several eighths of an inch of play- I don't know what the guts of the diff or the transfer case look like but I assume one or both of the DS bearings is/are farked. Front diff is also noisy/clunky when cornering in 4WD with wheels turned too far. Aft (main) driveshaft has no play at all- has a U joint which could be seized I guess, but the boot looks fine

 

[Mbrooks420]

If you are running in 4wd on a dry surface it will always bind and pop when turning. Continuing to do so will damage it.

 

[E.T.]

I'm aware of that, it gets turned off unless I am driving over snow. Noise is related to how sharply I turn, doesn't sound normal to me but then again the last 4x4 I drove was a Nissan which was actually built properly

 

[Mbrooks420]

Unless there is a lot of slip turning the wheels sharp will cause binding. Snow is irrelevant if there is traction.

If your Nissan was so nice, you probably should have bought another. I’m sure no Nissans have had a minor part failure.

 

[E.T.]

Fair enough. Turning off the 4x4 at junctions works. Should be an automatic feature really.

I Iooked for a Nissan, they were never sold here, presumably to save Ford's revenue.. Toyota got a foothold in Australia and ultimately Ford and Holden (GM) both collapsed down there because Australian built vehicles were just more expensive and less reliable than ones made in Asia, /especially/ Japan.

All of which is as maybe- there are dozens of late model donor vehicles at the local junkyard the total cost of two years' worth of replacement minor parts (like, say, an engine or a transmission) works out cheaper in the long run. Plus it's sort of fun periodically engineering out design flaws

 

[Mbrooks420]

Fair enough. Turning off the 4x4 at junctions works. Should be an automatic feature really.

I Iooked for a Nissan, they were never sold here, presumably to save Ford's revenue.. Toyota got a foothold in Australia and ultimately Ford and Holden (GM) both collapsed down there because Australian built vehicles were just more expensive and less reliable than ones made in Asia, /especially/ Japan.

All of which is as maybe- there are dozens of late model donor vehicles at the local junkyard the total cost of two years' worth of replacement minor parts (like, say, an engine or a transmission) works out cheaper in the long run. Plus it's sort of fun periodically engineering out design flaws

Does this happen in “4wd auto” or just in “ 4wd high” (presuming it has a high setting).

 

[E.T.]

Happens in "high"- I've never felt the system kick in when set to "auto" even on icy parking lots so I use the button just to be sure it's engaged (which may not be best practice).

 

[Mbrooks420]

If it works in high it should work in auto, it’s just an electric clutch locking up.(unless of course you have speed sensor issues, but that’d throw an code, and would probably effect the abs as well) I’d use auto, unless what you are passing through is considerably bad.

 

[TechGuru]

Happens in "high"- I've never felt the system kick in when set to "auto" even on icy parking lots so I use the button just to be sure it's engaged (which may not be best practice).

If you want to test the auto, floor it from a dead stop on a wet road, the front will kick in when the rear slips.

I've only had to drive on icy roads once since getting my Exp so far, left it in auto, never needed to kick in, I'm sure having a LSD in the rear helps a lot.

 

[E.T.]

Alright- thanks to both of you. Snow is simultaneously melting on the ground and falling from the sky here so I'll probably get a chance to do that test tomorrow.. The shaft isn't coming out until it dries up a bit anyway.