Gears... it was time! After some thinking and
larger tires planned for the future, it was almost a must to get a
lower ratio. We were also installing lockers so the gears and
lockers would be a good thing to do together. After the 1 ton axle
swap, the K5 had the axles 4.10 gear ratio but that still wasn't
good enough for what we were running and if we really wanted to run
larger tires, 4.10 wasn't going to cut it. When deciding on gears,
you need to know what tire size you will be running, as choosing
the correct gear ratio will get your vehicle back into its power
and torque band. We were in the market for new gears for project
"Potent Rodent". The gears we had were ok but with the tires we're
running, it didn't have enough power going up the rocky mountain
highways. On the highway, the gears made the engine run in a lower
band, which didn't provide enough passing power. When you're
passing a semi-truck on a double yellow and you suddenly see a car
coming, you NEED that power!
When the plan for larger tires came about, we quickly called on
National Drivetrain for their assistance on helping us choose the
proper gear ratio. They suggested a ratio of 4.88, which are about
perfect for larger tires that measure around 38". National
Drivetrain has qualified people who can assist anyone with this
type of selection. Not only do they carry gears, but also lockers,
transmissions, transfer cases, driveshafts, lift kits, shocks,
bumpers, and many other things as well. Their price, selection and
quality parts make it a must to check them out when shopping for
anything.
The new 14 bolt gears. These are Motive brand which
are a thick ring gear. By getting a thick ring we can use our
existing carrier.
Click picture for larger
image
New Dana 60 ring and pinion. These are made my
Dana\Spicer. Both sets can be purchased through National
Drivetrain.
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image
Most V8's are usually rated at 2000-2600 RPM for highway cruising.
The upper range will give you more power, which is what we wanted.
Here's how to calculate this number: Axle Gear Ratio X MPH X 336
X Overdrive / Tire Diameter = RPM
Here's what it looks like with 36" tires.
Ratio
MPH
336
Tire
Dia.
RPM
3.08
60
336
36"
1725
3.42
60
336
36"
1915
3.73
60
336
36"
2089
4.10
60
336
36"
2296
4.56
60
336
36"
2554
4.88
60
336
36"
2733
5.13
60
336
36"
2873
Here’s what it looks like with 38" tires:
Ratio
MPH
336
Tire
Dia.
RPM
3.08
60
336
38"
1634
3.42
60
336
38"
1814
3.73
60
336
38"
1979
4.10
60
336
38"
2175
4.56
60
336
38"
2419
4.88
60
336
38"
2589
5.13
60
336
38"
2722
We wanted around 2500 RPM at 60 mph with 38" tires
so 4.88 seemed the best choice for us. Since we aren't running OD,
we can't figure that in the equation. As you can see, 4.88 runs a
bit high with 38's, allowing more power. This would also be ideal
if a transmission with over drive was added in the future. The
choice for 4.88 gears with 38" tires became very obvious at this
point, especially since they will also allow slower crawling on the
trail. The consensus generally is that 4.56 gears would be fine
with 38's for highway power and mileage. 4.88 gears will give you
more power, but less mileage. After determining the correct ratio,
National Drivetrain set us up with the proper gears and install
kits. Dana/Spicer gears for the front and Motive gears for the
rear. The rear had to be a thick ring gear so our carrier didn't
have to be replaced. Since a new ARB carrier was going in the front
we didn't need to worry about the front. Sometimes when going to a
lower ratio, the carrier will need to be replaced. National
Drivetrain can tell you if you will need to replace the carrier or
not. If the carrier needs to be replaced, it will add to the cost.
This is another important factor to determine your desired ratio.
Gear Install Kits It's always a good idea to get an install
kit when upgrading gears. The install kits comes with all the
necessary parts to complete the job. This includes new bearings,
shims, seals, crush sleeves, pinion nuts, washers, ring bolts, and
gear marking compound. It really takes the headache out of trying
to order everything separately. It also gives piece of mind knowing
new bearings are installed. These kits are strongly recommended to
do job correctly. National Drivetrain can get these install
kits.
14 bolt install kit.
Click picture for larger
image
Dana 60 install kit.
Click picture for larger image
Lockers In the back, we decided on a Detroit locker which is
known for durability and strength. For the front axle, we wanted
something in the front that wouldn't hinder driving performance on
the street. Most lockers installed the front axle will have some
side affects when the hubs are engaged. Some are worse than others.
The most versatile locker is the ARB air locker. The well-known ARB
can be turned on and off, allowing completely open diff driving on
the pavement, and fully locked traction off-road. This means you
don't have to learn how to drive all over again around town, and
have the option to heighten your 4x4 challenge by not locking in if
you so choose. The design of an ARB locking differential is quite
ingenious. We would be running the ARB locker in the rear but ARB
does not have one for that application yet. National Drivetrain can
supply both Detroit and ARB lockers for most applications. Gear
installs are not for everyone "I want to put new gears in
myself. How hard is this?" We see this question asked so many
times. The thing is the gears have to be setup correctly, period.
If not set correctly, serious damage could occur. We were on the
verge of installing our own gears but after we found what’s
involved we changed our mind (read below). Although proper ring
& pinion setup can be accomplished at home, we really recommend
having a professional do the job. Use the right tool for the
right job Setting up a differential involves a lot of
measuring, disassembly, reassembly, adjusting, and remeasuring.
Aside from the tools needed to assemble and disassemble a rearend,
a good mechanic needs the right tools for making accurate
measurements. Having the right tools makes the job far easier while
the wrong tools can make the job miserable, if not impossible. When
working on a differential you will need a wide variety of special
tools. If you do not have the tools you need, they can often be
rented or borrowed. If you want to learn to build rearends or plan
on building them on a regular basis, then investing in good tools
is definitely worth the money. Using the correct tools, such as the
ones listed below, will not only save you time but also prevent
parts from being damaged.
Dial indicator
Genuine gear marking compound and a clean brush
Calipers or a micrometer
Bearing puller
Bearing press (or access to one)
Three foot long breaker bar or strong impact gun
Pinion nut socket
Six point cross pin bolt wrench
Pry bars for removing the carrier case
48 oz plastic dead blow hammer
Assorted brass punches
Center punch or number stamp for marking main caps
foot pounds torque wrench
inch pounds torque wrench
Not really considered a tool but the lift really
helps with the gear install. Everything is at eye level and easy to
get to.
Click picture for larger
image
A good bearing puller is needed when removing the carrier bearings,
and especially when the carrier shims are located between the side
bearings and the carrier case. I do not know of any way to
consistently set the backlash correctly without a good dial
indicator. Gear marking compound is sometimes difficult to find but
always worth finding. Dial calipers can be found on many tool
trucks, at hardware stores, and at Sears. A good inch pounds torque
wrench is an expensive investment for a single installation however
it is worth finding. A foot pound torque wrench can NOT be used for
setting the pinion bearing preload as it is not accurate at
settings that low.
A dial indicator like this is mandatory when
installing gears.
Click picture for larger
image
There are some tools that are not absolutely necessary. Bearing
race drivers, for example, are a tool where something simpler could
be substituted. A good bronze bunch (about 7/8" dia x 12" long)
works well for driving bearing races in and out. Just be careful to
remove any chips prior to assembly. Old inner and outer bearing
races can be used for driving in seals and guiding on bearings
during press operations. An old cross pin shaft can be ground to a
point on one end and used for driving out the pinion shaft without
damaging the threads. It is very important to accurately measure
backlash, pinion bearing preload, and bolt torque. If any of these
adjustments or torques is not correct, it could lead to early parts
failure. You should always use a dial indicator to measure the
backlash. Also be sure the measure the correct pinion bearing
preload by measuring it every time with an accurate inch pounds
torque wrench. What’s involved in setting gears? If
you really insist on giving it a shot, then here is some
information that should be helpful. When setting up a ring &
pinion there are four critical settings that need to be correct in
order to get proper setup and good gear life. They are: Pinion
depth (how close the pinion is to the ring gear), backlash (how
close the ring gear is to the pinion), pinion bearing preload (how
much bearing drag is on the pinion bearings), and carrier bearing
preload (how much bearing drag is on the carrier bearings). Given
enough time, just about any approach will work when setting up a
ring & pinion. However, you should adjust the four settings in
the following order so that the job goes faster with less
frustration. First, set the backlash using only light carrier
bearing preload. The proper preload can be added closer to final
assembly. Next, check the pinion depth by way of the contact
pattern. Make sure you use only real gear marking compound, as
other marking substances are difficult to read. There are many
theories about how to read the contact pattern, but we won't open
that can of worms now. After checking the pattern it is usually
necessary to adjust the pinion depth. After changing the pinion
depth, the pattern should be rechecked. The backlash may have to be
readjusted as the pinion depth is changed. It should be close to
specifications in order to get a good pattern reading. Once the
correct pinion depth is established, the pinion bearing preload can
be adjusted. When setting the pinion bearing preload on a crush
sleeve design differential, it is always necessary to use a new
crush sleeve every time the pinion nut is removed, or if the sleeve
is over-crushed. When installing the carrier, the same adjusters or
shims that are used to adjust the backlash are also used to set the
carrier bearing preload. Rather than trying to change the backlash
and preload at the same time, you should get the backlash correct
and then adding preload for the final assembly. If the carrier has
to be moved to set the backlash it is easier to remove if the
preload is not too tight. Once the backlash has been set, the
carrier bearing preload can be added. Some books give exact
specifications of how much preload to add to the carrier bearings.
If they call for 0.015" preload, a zero point must first be
established, and that is not easy either. You should set the
carrier bearing preload as tight as you can get it without damaging
the shims during installation. For screw adjuster type
differentials you should tighten to about 100 to 150-ft lbs. of
torque on the adjusters. Installation To do this procedure
correctly, we called upon Goins Automotive in Denver. National
Drivetrain can also perform correct installations but they're out
of state. Goins Automotive has extensive experience in both gear
and ARB installations. Goins Automotive also has an excellent
reputation regarding gear installs.
The shafts are removed from the 14 bolt.
Click picture for larger
image
The old ring before it's removed from the 14
bolt.
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image
Goins starts the installation by putting the K5 up on the hydraulic
hoist and removing the tires (we have to get one of these).
Starting on the rear axle, the existing the shafts were removed.
The carrier is removed by taking off the prongs that go in the
adjusting screws. Next, the differential adjusting screws can be
loosened. These have several holes that provide a location for
loosening. After the adjusting screws are loose, the main caps are
removed. Care must be taken when these are removed so they are
installed in the same manner. Some markings on these to show right
or left side and which end is up are a good idea.
The adjusting screws. These turn to tighten or loosen
the carrier. Much easier compared to shims.
Click picture for larger
image
The pinion is removed from the 14 bolt and the front
part of the housing must be pressed out.
Click picture for larger
image
After the carrier is out, the ring gear is separated from the
carrier. The carrier is taken apart and the spider gears are
removed. The Detroit locker is then installed and the new ring gear
is installed using Loc-tite.
The ring gear is removed from the 14's
carrier.
Click picture for larger
image
The new ring gear is installed on the
carrier.
Click picture for larger
image
The pinion gear is then removed. With the GM 10.5" 14 bolt, part of
the front housing comes off and has to be removed from the old
pinion. This step is done by using a press. Great care must be
taken to avoid any damage to the front housing. After the pinion
shaft is removed, the pinion bearings and races are removed. Once
the carrier and pinion shaft were removed, the case was thoroughly
cleaned to remove any oil, grease and metal shavings. The front
housing part is also cleaned. The new pinion is then installed in
the front housing along with new bearings. The other pinion bearing
is installed next and the pinion is installed in the housing.
The new pinion is installed. Shims are installed at
this point.
Click picture for larger
image
The new ring and carrier is installed. Be careful not
to drop it!
Click picture for larger
image
Here's what the 14 bolt pinion shims look like. This
spaces the pinion to achieve the correct lash.
Click picture for larger
image
Major toque is applied to the pinion nut to crush the
sleeve on the pinion. This is a critical step since you can't
change you mind if you went too far. It would be difficult to do
this on the ground.
Click picture for larger
image
Install the carrier back into the differential housing and check
for pinion depth and backlash. Once everything is set up correctly,
apply some marking compound to the ring gear and rotate the ring
gear until the marking compound passes the pinion shaft in both the
forward and reverse direction. The marking compound will show how
the ring gear/pinion shaft wear pattern is. This is the most
difficult and the most critical process in setting up new gears.
The wear pattern should look similar to the picture below.
The dial indicator is used to check the lash.
Click picture for larger image
The final check is done using gear marking compound.
This is what is should look like.
Click picture for larger
image
After everything looks good, applying major force on the pinion nut
sets the crush washer. This usually involves a very long breaker
bar or torque wrench. It took two guys to do this. One guy to hold
the yoke and the other to tighten the pinion nut. The lift also
helped. This would be difficult to do on the ground.
The front axle is started by removing the hubs,
calipers, spindles and axle shafts.
Click picture for larger
image
A little force is applied to the old carrier to
remove it.
Click picture for larger
image
The pinion is removed and the inside is cleaned using
brake cleaner.
Click picture for larger
image
The new pinion is installed with the correct
shims.
Click picture for larger
image
For the front end, we started by removing the brake calipers along
with the axle hub nut and hub assembly from the steering knuckle.
The spindle is then removed along with the axle shafts. The tie rod
is also moved out of the way by taking off one side. Remove the
bearing caps and slide the entire carrier out of the differential.
Remove the old ring gear and install the new 4.88 ring gear onto
the new ARB carrier using the supplied ring gear bolts. Use
loc-tite and torque to specs. The old bearings are removed and
replaced with new bearings. Remove the old pinion and mic the shims
that were used. The old bearings and races were replaced with new.
The new pinion is then installed using the old shim thickness as a
starting point for the pinion depth.
The Dana 60 shims. The larger shims are for the
carrier and the smaller shims are for the pinion.
Click picture for larger
image
To start with, you can measure the old shim thickness
with a mic and try to mount the new pinion with the same
thickness.
Click picture for larger
image
After the correct pinion depth is achieved, the new ring and lock
is then installed. This takes some time to get the correct lash
since you must remove the carrier each time any adjustment is made.
One thing you can do if you're using new bearings is to hone the
inside of the old bearings by grinding the inside a little so the
old bearing will not have to pressed on each time different shims
are needed. After the correct shims are found, new bearings are
then pressed on. You really appreciate the 14-bolt design after
doing this step. The final installation of the bearing caps is
performed and another check for the backlash is done. The final
stages involve hooking up the ARB, which is in another article at
www.off-road.com/chevy/reviews/arb
. The axle shafts, spindles, hubs and calipers are then
reinstalled. Be sure to use quality oil and a locker additive if
required.
The new ring is installed on the new ARB locker. The
old carrier will not be used.
Click picture for larger
image
The new ring and locker are installed along with the
shims. The shims are difficult to install since they're so
thin.
Click picture for larger
image
New Gear Break-In
For superior protection, we used this oil from
Lubrication Engineers. This oil is rated very high among all the
other synthetics.
Click picture for larger
image
In most stock vehicles with stock tires there is seldom a risk of a
burned gear set. For those of us who modify and use our trucks,
there many situations that can contribute to burned gear syndrome.
Motorhomes, towing, tall tires, and high numeric gear ratios (4.56
& up) can all generate a lot of heat and cause the gear oil to
break down. The greatest damage to a new gear set results when it
has been run for ten minutes or more during the first 500 miles and
the oil is very hot. Any heavy use or overloading while the oil is
extremely hot will cause it to break down and allow irreversible
damage to the ring & pinion. In order to make them run cooler
and quieter, new gears are lapped at the factory. However, they are
not lapped under the same pressures that driving creates. The loads
generated while driving, force any microscopic high spots on the
gear teeth back into the surface of the metal. This is called "work
hardening". Work hardening is similar to forging in the way that it
compresses the metal molecules into a very compact and hard
formation. This can only be accomplished if the metal surfaces are
lubricated and the gear temperature stays cool enough that the
molecular structure does not change. If the temperature of the
metal gets hot enough to change the molecular structure, it will
soften the surface instead of hardening it. This may seen like a
balancing act but it all happens easily & passively as long as
the oil keeps the gear cool while it is breaking in. Some of the
synthetic oils on the market today can help a gear set live longer.
These oils will continue to lubricate at temperatures where many
crude oils break down. Even with synthetic oils, you should still
follow the procedure for breaking in a new gear set: After driving
the first 15 to 20 miles it is best to stop and let the
differential cool before proceeding. Keep the vehicle at speeds
below 60 mph for the first 100 miles. You should put at least 500
miles on the new gear set before heavy use or towing. During the
first 45 miles of towing it helps to go about 15 miles at a time
before stopping to let the differential cool for 15 minutes before
continuing. This is necessary because not all of the gear tooth is
making contact until it is heavily loaded. When towing, the teeth
flex to contact completely, and cause the previously unloaded
portion of the teeth to touch and work hardens. All of this may
seem like paranoia, but it is very easy to damage the ring &
pinion by overloading before the teeth are broken in. If you take
it easy on a new ring & pinion and keep it full of high quality
oil, it should last a lot longer. It is a good idea to change the
gear oil after the first 500 miles in order to remove any metal
particles or phosphorus coating that has come from the new gear
set. This is cheap insurance and a good time to discover any
problems before they grow to disastrous proportions quality parts
and service. Impressions The process of installing and
properly setting up new gears really isn't that difficult, assuming
you have some mechanical know-how, have the correct tools and a bit
of patience. It took about 9 hours for a professional shop to
install both sets of gears along with the new lockers. Plan on
taking twice as long if you've never done this before. If you do
plan on doing a gear swap yourself, we'd recommend contacting
someone who's done it before and have them help you out. This is
one project that can lead to severe carnage if not done correctly.
The difference the new 4.88 gears made is pretty remarkable,
compared to the 4.10 gears we were running. The freeway RPM's are a
bit higher, but at least we got more power on the hills and we're
now ready for 38" tires! With the 4.88 gears, my crawl ratio went
from 53:1 (4.10 gears) to a respectable 63:1! Crawl ratio is
calculated using the following formula: Transmission 1st gear X
Transfer case low range X Gear ratio=crawl ratio (6.55 x 1.98 x
4.88 = 63:1). As soon as the Blazer left the shop, you could tell
it had more get up and go! Highway driving is really nice, although
the engine revs a bit high at cruising speed, resulting in a louder
ride. City driving is also quite nice as there’s extra power
to pass and get off the line quicker if needed. Once 38's are
added, the gearing should turn out just about perfect. We had the
opportunity to test the whole setup in the mountains of Colorado.
This provided plenty of opportunity (necessity!) to evaluate the
difference between the gear ratios and the performance of the
lockers. It was simple to compare the driving experience with that
of the newly stuffed axles. Throwing the NP205 into LO gear and
cruising for hours was awesome! The 4.88 gears allowed slower
approaches to obstacles, required less gas to overcome them, and
less braking coming down the other side. All around, the gearing
was a massive improvement. It was also evident on steep descents,
as I could brake hard and the engine would not stall as before, but
would instead crawl slowly down the rock. We ran most of the trail
with the front ARB open but when locked, you can really it feel it
working and it made it feel like you were unstoppable. Turning was
a chore and it seemed that a touch more gas was needed to get the
K5 moving. Some of the difficult parts that would have been a
problem before could easily be walked over now. It’s taking a
while to get the Blazer to this level. That can be said with any
number of modifications, but lower gearing and locking
differentials are really a big step in performance enhancement,
both on the trail where it really counts, and on the road, where
driving is still as pleasant as it has always been. For more
information on the new gears or the lockers mentioned here, contact
National Drivetrain.
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