4wd whining noise.

[Hypnotoad]

I have a 2004 TB. When in 4wd I can hear a whine noise from the drive train at low speeds. I noticed the sound last year and thought it was normal, but this winter it seems to be louder. Then, I realized it's happening in AWD also, even when it isn't engaged.

Even after reading through many threads, I don't understand how the operation of AWD and 4WD differ from each other, but why might the whine sound be happening when the AWD is selected on the switch, but isn't engaged? Does this help narrow down where the sound is coming from? I'm thinking the sound is coming from the splined disconnect, but can't be sure.

Any help is appreciated.

 

[The_Roadie]

That system is my specialty, as it is for many offroaders. Read this first for a detailed theory of operation: Offroadtb.com Transfer Case Operation: NVG 226 (NP8)

Here's more info on the splined disconnect and how they can fail: Offroadtb.com Front Axle 4WD Disconnect

In a nutshell, In 2WD, the splined disconnect is not connected, but the driver's side wheel spins its CV shaft and thus some internal parts in the front differential. All the time. So you have to keep up on front differential fluid changes, we recommend every 100K. How many miles do you have, and how's your differential fluid level? Also how's your rear differential while we're on the subject?

The passenger side tire always spins its CV shaft, but the splined disconnect does not couple it to the intermediate shaft that goes through the tube cast into the oil pan.

In A4WD, 4HI, and 4LO modes, the splined disconnect engages, and now the passenger side tire is spinning the intermediate shaft, and more parts move inside the front differential. A differential with low fluid or internal damage tends to make more noise in these modes than in 2HI. But it's possible for a bad differential to make noise even in 2HI. Some folks assume that nothing inside moves when you're in 2HI mode, but that's not true. Only if we had disconnectable HUBS would that be true, and they didn't design those in for us.

Your other major source of noise is the transfer case, with MANY moving parts, especially a clutch pack. The major difference between A4WD and 4HI mode is the position of the clutch pack. In 4HI, the clutch is engaged fully, and sending as much torque forward to the front driveshaft as it's sending backwards to the rear. In A4WD, the TCCM is looking at wheel speed sensors, and sending only about 5% torque forward under normal conditions. When it sees the rear wheels spinning faster than the front, the TCCM assumes there's a need for more torque to be sent to the front, it commands the transfer case encoder motor to move a lever on the transfer case that adjusts the pressure on the clutch pack, and the clutches engage and (supposedly) smoothly send more torque forward to eliminate the wheel spin.

The constant movement of the clutch pack, and constant partial engagement of slipping clutches results in early transfer case destruction for nervous owners who leave their vehicles in A4WD mode when it's not absolutely needed. Sometimes they die in 6 months to a year. Lesson: A4WD mode is NOT AWD. It's not a Subaru.

The other huge note is that the transfer case fluid change interval is a surprisingly short 50K. I can't stress this enough - deferring the fluid change can cost you a transfer case. What's your situation on fluid changes here?

 

[Hypnotoad]

Both differentials and transfer case fluids were changed at 70,000 miles, which was about 10k miles ago. I haven't checked the fluid levels though, I'll have to do that later.

I did read that article already, but I had a hard time understanding it all. I'm curious why the noise would be exactly the same in A4WD and 4HI, but completely gone in 2WD. I figured the splined disconnect because it's always engaged in A4WD and 4HI and not while in 2HI.

So, now it sounds like it could be something in the transfer case too.

 

[The_Roadie]

Nothing is ruled out at this point, even the front diff. The identical parts are turning in A4WD as in 4HI. Fewer parts are moving in 2HI. The only difference between A4WD and 4HI is the pressure being put on the TC clutch pack by the encoder motor. Could be a bearing or gear, or indeed something inside the splined disconnect. Should be able to localize it in ten minutes on a lift.

 

[Hypnotoad]

Thanks for the help, I have a much better idea of what to look for now. I'll have to break out the old stethoscope and stick it up on jack stands.

 

[autocad712]

That system is my specialty, as it is for many offroaders. Read this first for a detailed theory of operation: Offroadtb.com Transfer Case Operation: NVG 226 (NP8)

Here's more info on the splined disconnect and how they can fail: Offroadtb.com Front Axle 4WD Disconnect

In a nutshell, In 2WD, the splined disconnect is not connected, but the driver's side wheel spins its CV shaft and thus some internal parts in the front differential. All the time. So you have to keep up on front differential fluid changes, we recommend every 100K. How many miles do you have, and how's your differential fluid level? Also how's your rear differential while we're on the subject?

The passenger side tire always spins its CV shaft, but the splined disconnect does not couple it to the intermediate shaft that goes through the tube cast into the oil pan.

In A4WD, 4HI, and 4LO modes, the splined disconnect engages, and now the passenger side tire is spinning the intermediate shaft, and more parts move inside the front differential. A differential with low fluid or internal damage tends to make more noise in these modes than in 2HI. But it's possible for a bad differential to make noise even in 2HI. Some folks assume that nothing inside moves when you're in 2HI mode, but that's not true. Only if we had disconnectable HUBS would that be true, and they didn't design those in for us.

Your other major source of noise is the transfer case, with MANY moving parts, especially a clutch pack. The major difference between A4WD and 4HI mode is the position of the clutch pack. In 4HI, the clutch is engaged fully, and sending as much torque forward to the front driveshaft as it's sending backwards to the rear. In A4WD, the TCCM is looking at wheel speed sensors, and sending only about 5% torque forward under normal conditions. When it sees the rear wheels spinning faster than the front, the TCCM assumes there's a need for more torque to be sent to the front, it commands the transfer case encoder motor to move a lever on the transfer case that adjusts the pressure on the clutch pack, and the clutches engage and (supposedly) smoothly send more torque forward to eliminate the wheel spin.

The constant movement of the clutch pack, and constant partial engagement of slipping clutches results in early transfer case destruction for nervous owners who leave their vehicles in A4WD mode when it's not absolutely needed. Sometimes they die in 6 months to a year. Lesson: A4WD mode is NOT AWD. It's not a Subaru.

The other huge note is that the transfer case fluid change interval is a surprisingly short 50K. I can't stress this enough - deferring the fluid change can cost you a transfer case. What's your situation on fluid changes here?

Roadie -

Based upon the expertise that you obviously have on these systems, I was just wondering your thoughts may be on my issue, and if you might consider sharing.. '03 TB 4.2 A4WD. The system is "whining" on me, predominately at lower speeds in 4HI as well as "sometimes" in A4WD. (Think, motorized toy car being manually pushed along on a flat surface). Never in 2HI. Now, oddly enough, this occurs on wet/snowy pavement, but when I operated the truck in PURE snow (4HI) the noise did not occur at all. I was driving up to 35mph over this fresh driven snow, and not a sound. The tires in the rear are "very" worn, and the tires in the front are basically perfect. I have heard that this can be a cause of the 4wd whine. Front diff fluid and TC fluid are brand new. (6 days ago) Just wondered if you might be able to give me some thoughts. Not too familiar with 4wd, you apparently are. My thanks in advance.

 

[The_Roadie]

Yep, the whining may be the transfer case clutches being scrubbed on each other by the slight difference in tire diameter. I'd put one worn and one good tire in the front, and the same arrangement inthe back. Don't go too far - just enough to test the theory. And get a pair of new matching tires and get rid of the worn out ones ASAP. Otherwise you have some interesting behavior I don't recall hearing much about before.

Also check 4LO mode and see if the whining is more related to ground speed than engine RPM. In LO range, there's a 2.7-to-1 reduction gear set involved.

 

[autocad712]

Yep, the whining may be the transfer case clutches being scrubbed on each other by the slight difference in tire diameter. I'd put one worn and one good tire in the front, and the same arrangement inthe back. Don't go too far - just enough to test the theory. And get a pair of new matching tires and get rid of the worn out ones ASAP. Otherwise you have some interesting behavior I don't recall hearing much about before.

Also check 4LO mode and see if the whining is more related to ground speed than engine RPM. In LO range, there's a 2.7-to-1 reduction gear set involved.

Hey Roadie, thanks for responding.
New tires now in rear. Same whine noise. Both in 4hi and 4 lo. No Service lights coming on. 4 wheel engages, just makes this whine. Also, once while it was in the middle of doing this, I attempted to shift from 4hi back into 2hi, and the switch blinked and refused to switch into 2 hi until vehicle was stopped. Then it went right in. Stumped..

 

[The_Roadie]

Failure to shift modes points to an intermittently bad encoder motor or something inside the transfer case causing high force being required on the shift shaft. (Say that fast ten times! :wootwoot If I was worried about the noise, I'd get it up on a lift to confirm it's inside the TC, then start looking for a used one for a swap.

 

[autocad712]

Failure to shift modes points to an intermittently bad encoder motor or something inside the transfer case causing high force being required on the shift shaft. (Say that fast ten times! :wootwoot If I was worried about the noise, I'd get it up on a lift to confirm it's inside the TC, then start looking for a used one for a swap.[/QUOTe

Would a bad differential (front) cause the shift to require that higher force? (Also, it didn't give up trying and throw a service 4wd light, which I found odd. I think usually if they cannot shift, they just say "oh well" and light up a 4wd light) ANYhow..Going to take it to our local trans shop & get it up in the air and see what they say about the TC. Sometimes one has to "point" these folks in a given direction, and I am using your opinion to accomplish that. Thanks Roadie.

 

[IllogicTC]

Would a bad differential (front) cause the shift to require that higher force? (Also, it didn't give up trying and throw a service 4wd light, which I found odd. I think usually if they cannot shift, they just say "oh well" and light up a 4wd light) ANYhow..Going to take it to our local trans shop & get it up in the air and see what they say about the TC. Sometimes one has to "point" these folks in a given direction, and I am using your opinion to accomplish that. Thanks Roadie.

It shouldn't. The connection made to the front within the transfer case is just applying the clutch pack, there's no motion required outside of the transfer case for this.

Likewise, the front axle disconnect requires either no or extremely little movement in the front differential to click in, on the order of maybe six inches or less of vehicle travel from a stop.