my 98 QX4's transfer case makes a huming noise when switched to 4wd auto or 4wd lock. makes the nosie wether it is moving or standing still. however it does not make the noise when it is in park or neutral while in 4wd auto or lock. Nor does it make the noise when I hit 27 - 30 mph. is this normal noise or something going bad? does anyone else's QX4 make a huming noise when 4wd is switched on?

There is a normal noise that should be heard and this is the transfer motor turning an oil pump inside your tc to lubricate it. But if the noise is outerly noisy or screeching then a problem exists...

Most probably something like a seal or bearing is failing in your secondary transfer case oil pump.

The transfer case you have atx14a, is lubricated with 2 methods. Either by an electric motor or by the movement of the truck past a certain mph that is moved by the main driveshaft.

Now, when you switch to 4x4 and you stay still, then the electric motor will run and turn the oil pump shaft to lubricate the TC. once you start moving, the electric motor stops and the movement of the truck makes the oil pump shaft turn.

here's an exerpt from the fsm :

TRANSFER MOTOR
NATF0067S01
1. The transfer motor drives the sub-oil pump to provide proper lubrication and oil pressure control when the
vehicle is at standstill, during low-speed operations or is being driven in reverse.
2. The main oil pump is operated by the driving force of the mainshaft. In other words, sufficient oil pressure
buildup does not occur when the vehicle is at standstill or during low-speed operations. While the vehicle
is being driven in reverse, the main oil pump rotates in the reverse direction. Therefore the main oil pump
does not discharge oil pressure. During any of the above vehicle operations, the transfer motor drives the
sub-oil pump to compensate for insufficient oil pressure.
3. The transfer motor operates as follows:
1) The motor relay turns OFF in the 2WD mode.
2) The motor relay operates as described in the table below in modes other than the 2WD mode.
Table 1
PNP switch “R” position VFF (Vehicle speed) A/T position Motor relay drive command
ON — R ON
OFF
0 km/h
Positions other than the “P” or
“N” positions
ON
—
“P” or “N” position (See Table
2.)
—
0 < VFF % 30 km/h — ON
30 < VFF < 35 km/h — HOLD
35 km/h % VFF — OFF
Table 2
A/T position N-4L SW 4WD mode
Throttle position
0 - 0.07/8 0.07/8 - 1/8 1/8 - MAX
N
OFF
LOCK (4H) ON ON ON
Positions other than
the LOCK position
(2WD or AUTO)
See NOTE. HOLD ON
ON — See NOTE. HOLD ON
P — — See NOTE. HOLD ON
NOTE:
OFF (after 2.5 seconds have elapsed.)
4. 4WD shift switch, PNP switch, Neutral-4LO switch, vehicle speed sensor and throttle position sensor are
used in conjunction with the transfer motor.


The oil pump is called at nissan a transfer motor. It is accessible from outside the transfer case (so you do not need to open the TC).. I would have a nissan tech have a look at this since you do not want your transfer motor shaft to seize or grinde more each time you put on 4wd... One good news is though, is that as long as you stay in 2wd, you will not make the part go worst... it is only used in 4x4 mode.

But like i said, a certain noise is normal...
S.

Yeah I recently changed my transfer motor, when I got it out it was definately seized up. I got lucky and found one at the junkyard for $7, a new replacement would have been almost $200. There is a tube connected to it, possibly vacuum, anyone know it's purpose?

asnorton can you identify that tube where from where to? I have looked over schematics, none shown but ...there is a wait signal may be pressure? Attached to the transfer case is front wheel rev sensor, neutral 4 LO, ATP sw, , wait detection sw, transfer fluid temp sensor, line pressure sw, and clutch pressure sw.

Since pressures are monitored that hose may be feeding the many sensors related to the ATF in the transfer case.

At 3 liters per book and my experience is 2 liters to change out I drop the transfer oil every 2 years, same as transmission, it is cheap insurance. Transmission can easily hang up with debris in and around valves as does the ATF in the transfer case. Each and every refill indicates debris in the oil in both trans and transfer boxes and better out than in.

The transfer motor will complain on low fluids. If the ATF is burned on either transmission or transfer carbon build up will take place and particles of combustion are a not very good thing for hydraulics even slow burn is bad. The by-products within the ATF become things that cause greater friction. And friction is what is used in transmissions and gear boxes or transfer boxes.

A cheap fix may be a simple oil change.

I use a manual 1 liter pump that I suck up the ATF and shove into the transfer case. The automatic transmission is an easier fill by hanging a bottle of fluid and piping it into the dipstick check pipe, let it hang there while you do other work and remember your quantity going in.

Apparently it is a "breather tube".

To atmosphere?

Old thread, I know. But there isn't very many and I know my chances are extremely low on getting an answer. But, do you guys have a part number for this transfer motor? Mine is making the loud whine just like stated above, same time, same noise. But I can't find the part or part number and none of my parts stores have a clue what I'm talking about. What do you expect for 12 bucks an hour i guess. Mine is a 98 qx4 auto trans lsd rear 202,000 miles. This car is old but I baby it and it is the most reliable rig I have ever had so I want it fixed

There's apparently three variations of this pump -depending on production date from 1997-2001:
https://www.infinitipartsdeal.com/parts ... 0w421.html

Still available

Geren8509 wrote: ↑

Fri Sep 30, 2022 10:22 am

... part number for this transfer motor...

I think the transfer motor part number is 33251-2W51A (Device Assy-Transfer Control) for the '98 QX4 but it's a discontinued item.