Warning in advance: this may seem odd. (It's also a tad long and there is no tl;dr option.)

Until a week ago, I was 99% sure that I had a transfer case that was singing its own funeral dirge. For the last year, from 45 to 70 mph, there was a medium-loud (and rather head-splitting, after a while) singing whine that depending on ground speed and not the pavement surface. In short: I had what most people would think of as early-stage, classic, transfer-case whine.

Then my ACD/AYC pump went from mostly-dead to all-dead. While that was sad, I've now noticed that what I thought was transfer-case whine is gone. The car is freakishly silent when cruising at 65 mph. I cannot be sure that the two changes happened at the same time (because I wasn't thinking about this and didn't drive on the highway for at least a week after the pump fully died), but it sure seems an unlikely coinky-dink to me.

One question and one request:

has anyone else noticed a significant decrease in ground-speed-related noises when their ACD/AYC pump died?

would anyone with a working pump but some driveline noise (preferably that which most people would blame on the transfer case) be willing to pull the fusible link on their ACD/AYC pump and go for a back-to-back drive? (Note: I'm not talking about back-to-back between my car and yours; I'm asking you to try [temporarily] disabling your ACD & AYC and seeing if that reduces the your noises.)

TIA

 

sigh

 

why would the t-case whine stop at 70mph?

 

I've never had any noticeable noises before/after my ACD pump died. Once my car is out of the body shop, I'll pm you and try and help you out if I can.

On a side note, the ACD does pump into the clutch packs in the t-case iirc. Could the sound have been the pump at all?

 

Apologies. I have no idea if it does stop at 70 mph; it's just that my data stops at that speed due to (legal) speed limits. I can't hear anything over the rocks banging off the bottom of the car in the only situation where I've been over 70 mph in the last year or so.

 

Thanks, but what I really need is someone with transfer-case whine to pull the fuse to the pump and drive their car for five minutes. I would like to know if running without a working pump can reduce driveline noises in other cars.

You are correct that the ACD's clutch is in the transfer case, which is part of why I'm curious whether a dead ACD/AYC pump can affect the noises it makes. The clutch is separated from the gears that do the whining, but they do share some fluid.

 

I gotcha. Is it only in 5th gear, or any gear at those speeds? And is your noise completely gone now?

 

It was in any gear for me; ground-speed-dependent, which is exactly what you get with a dying T-case.

And, yes, as freakish as this may seem, the car is dead silent now. The only other difference from before (besides the pump dying) is that I have been beating on the car on gravel and dirt. Maybe I shook something up inside there. But that seems doubtful.

 

When you were on dirt/gravel, did you change the setting to "Gravel" or did you leave it in "Tarmac" mode? Might have burned something up

 

Um, when the pump is dead, the mode is irrelevant. In fact, you can no longer select a mode.

 

wow, that's pretty strange the it is now dead silent. I have a whine noise from like 58 - 65mph. I can only hear it in 5th when my foot is as light on the throttle as I can go before being completely off and engine braking. As soon as I give it say like... > 5% throttle the noise goes away. It might make it in 4th too but the rpms are too high to hear it over the exhaust I guess. Think it's the same as yours? If so, I could try the fuse thing.

 

Yep. That's the sort of noise I'm looking for. Please pull the fuse and take a drive.

In case you're wondering, the reason that the noise also depends on throttle-position is that different amounts of torque going through the T-case alters the force on the teeth.

Thanks.

 

Did you ever get this figured out?

 

My ACD pump made sounds like a slowly dying animal before it went out. I would think that might be what you were hearing.

 

I'm having the same whine...again with my X. It seems to only be bad when it's really cold outside and the whine can last for 10 seconds. As soon as i tap the brakes, the noise stops...sometimes coming back and sometimes going away. It usually happens when i'm below 3k rpms, regardless of the gear and if the clutch is pushed in or not. I originally thought it was my transfer case going out too, but it's been checked and the fluids are fine. I just find it weird that the only way to stop the whine is to step on the brakes...

Anyone else having this situation??