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This differential wasn't serviced and look
what happened! A new differential costs
about $1,500 plus $500 labor, and it's not
a DIY repair.
If you have a pickup or an SUV, here
are a few maintenance tasks you
can do yourself to prevent expensive
repairs. First we'll show you how to
change the oil in two often-neglected
members of your power train: the differential
and the transfer case. If you
skip this maintenance, you may end
up with an expensive ($2,000) metal-to-
metal experience (see photo).
Do it yourself on a Saturday morning
and save $150 in shop charges.
Second, we'll show you what to do
when you flick the switch to engage
your four-wheel drive and nothing
happens. You likely need a new shift
motor, and believe it or not, replacing
it is easy. And finally, for that stupid
tailgate that either won't open or won't
latch shut, check out the fix below.
Change differential oil
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Photo 1: Drain oil
Set a drain pan under the differential
and remove the cover bolts, starting at
the bottom. Hold the cover in place while
you gently pry the bottom edge out
enough to start draining the old oil.
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Photo 2: Add RTV sealant
Squeeze a generous bead of RTV
sealant around the edge of the cover
and on the inside of bolt holes (gasketless
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Photo 3: Tighten bolts
Tighten the bolts to specs with a
Note: We replaced the
old, rusted-out cover with a new one.
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Photo 4: Add new oil
Remove the fill plug, then add the
friction modifier and new gear oil.
Tighten the fill plug to the manufacturer's
Start by locating the stamped metal ID
tags on your front (four-wheel drive)
and rear differentials. Write down the
codes and take them to the dealer or
auto parts store. The parts people need
the codes to select the right gasket,
sealer and oil for your differential. The
ID tag also helps them determine
whether your differential is the “imited-slip”
type, which needs a friction-modifying
additive. Limited-slip differentials
transfer power to the opposite
wheel if one spins. The friction
modifier makes the mechanism work
smoothly. While you're shopping, also
pick up a “suction” gun to inject
the new oil and a tube of RTV (room
temperature vulcanizing) sealant to
reseal the gasket or form a new one.
Raise your truck and support it with
jack stands. If your differential is equipped
with a drain plug in the cover, you can
simply remove the plug and suck out
the old lubricant with a suction gun.
However, most newer-style differentials
don't have a drain plug and you
must remove the cover to drain them.
Place a drain pan under the differential
and remove the cover bolts, starting
at the bottom and working toward
the top. With the bolts out, hold the
cover while you gently tap it with a
rubber mallet or pry it off with a gasket
scraper. Once the oil has drained, use
paper towels to soak up any oil pooling
at the bottom of the differential
case. Don't spray the inside of the differential
with any type of cleaner—it can damage seals and clutches and
wash away critical start-up lube from
gear and bearing surfaces.
Use a gasket scraper or putty knife to
remove the old gasket or RTV sealant
from the housing and cover mating
surfaces. Do a final cleanup by spraying
a paper towel with aerosol brake
cleaner and wiping off any traces of oil
from the mating surfaces.
Then apply a thin coat of RTV
sealant to the differential and press the
gasket into place. Install the cover and
torque the bolts. If your vehicle calls
for RTV sealant instead of a gasket,
apply a generous bead on the cover,
making sure the bead surrounds the
bolt holes. Quick-curing RTV “skins”
over in as little as 15 minutes, so apply
the cover and torque the bolts right
away. Overtightening the bolts can squeeze out all the RTV and result in
leaks, so use a torque wrench. Proper bolt torque is critical to maintaining
a good cover seal. To find the
bolt torque specifications for your vehicle,
consult a shop manual or use an online repair manual (search for “online repair manual” for your truck or car model).
Read the directions on the RTV
package to determine the minimum
“curing” time before refilling with
fresh oil. Once the RTV has cured,
refill the differential to the right level
(refer to a shop manual). Always add
the friction modifier first and then top
off with the gear oil.
Change transfer case oil (four-wheel drive only)
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Photo 1: Drain the oil
Hold the plug near the drain so you can
quickly recap it if you need to spread
out the drop cloth.
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Photo 2: Refill the fluid
Use a suction gun to inject
new fluid if you don't
have enough space to
fit a funnel with a
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Use a suction gun to inject fluid in tight spaces.
The transfer case is located at the rear
of the transmission, and its job is to
“transfer” power to the front and rear
drive axles when you shift into four-wheel
drive. But the gears inside the
transfer case spin even when you're in
two-wheel drive. So it's important to
change the oil on schedule, even if you don't use four-wheel drive very often.
Place a drop cloth and drain pan in
the area under the transfer case before
you remove the drain plug—this can
be a messy job. The drain plug on this
Ford truck has a recessed 3/8-in.
square hole. To remove that style plug,
simply insert the end of your ratchet
and loosen. Other manufacturers use
hex-head drain plugs. Use a six-point
socket for that style.
To refill the transfer case, use a funnel
with a flexible spout or buy an
inexpensive suction gun to inject the
fresh fluid. Check your shop manual
for the type of fluid to use and the
proper fill level. Torque the drain plug
to specs when you're done.
Replace a transfer case shift motor
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Photo 1: Change motors
Remove the old shift motor and move the new motor into
place so it slides onto the shaft. Install the retaining bolts.
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Photo 2: Reconnect wiring
Tighten the bolts and reconnect the electrical connector.
Then go for a test drive to confirm it's working properly.
If your four-wheel-drive truck shifts
electronically (push button or dial),
the shift motor does the work of moving
the gears into and out of 2-WD,
4-High and 4-Low. When the shift
motor fails, your transmission will be
stuck in either two- or four-wheel
Diagnosing a shift motor problem is
easy. Refer to a shop manual wiring
diagram and follow the procedure for
checking for power at the motor. If the
motor is getting power but not
responding, replace it. It takes less
than an hour, and if you use an after-market
replacement motor, you can
save almost $200 by doing the job
yourself. Check with an auto parts
store, dealer or online for
In most cases, the motor is mounted
on the back of the transfer case and is
held in place by a few small bolts.
Follow the instructions in your shop
manual to move the transfer case into
the proper gear before removing the
Then disconnect the electrical connector
and remove the shift-motor
retaining bolts. The motor should pull
straight off the shaft. If your shift
motor has an interior ground wire (a
black wire that goes from the shift
motor to the inside of the transfer
case), simply cut it and splice it into
the new wiring connector. Solder the
splice together and be sure to seal it
with heat-shrinkable tubing to keep
the connection watertight.
Finish the job by applying a light
coat of RTV sealant around the edge of
the motor flange. Slide the new motor
onto the shaft, install the bolts and
tighten to specs. Reconnect the electrical
connector, and Bob's your uncle!
Lubricate the tailgate mechanism
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Photo 1: Spray lithium grease
Aim the spray-can straw so lithium
grease soaks the cam/lever area.
Then spray all the other pivot points on
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Photo 2: Lubricate latches
Spray the locking latch and spring
with grease. Open and close the
tailgate several times and spray the
Tailgates take a lot of abuse and
swallow a lot of debris from your
weekend projects. When that debris
finds its way into the lock and latch
mechanisms, you end up with a
tailgate that either won't open or
won't latch shut. It's an easy fix that
you can do with a socket set and a
can of spray lithium grease.
Start by removing the access
panel on the tailgate. (If you have a
bed liner, you'll have to remove the
tailgate section before you get to the
access panel.) Once the cover's off,
use compressed air to blow off the
lock mechanism. Then apply a liberal
coat of lithium grease to the
cam/lever area and all pivot points.
Operate the tailgate handle several
times to work in the grease and then